Chapter 9: Searching For The First Hominins
Genetic evidence suggests that the Hominin clade arose 5-7 million years ago (pp 229). This chapter deals with attempts to identify the earliest hominins.
The Moving History of the Missing Link
The missing link, transitional species between apes and humans, has changed throughout history. Initially it was thought to be Homo neanderthalensis, but we now know that they were relative late comers in history. Next Pithecanthropus erectus was thought to be a possible candidate for the “missing link”; it exhibited many apelike and humanlike characteristics. The point here is that since the idea arose of missing links that the dates have been pushed back considerably from roughly 150,000 years ago (Home neanderthalensis) to between 6 and 7 million years ago, with the discovery of Sahelanthropus tchadensis. This specimen is congruent with what genetic evidence is telling us, and furthermore it was found in Africa, which is also parsimonious with what most paleoanthropologists believe.
Major Sites of Early Hominin Fossils: South Africa, East Africa, and West Africa
All of the early Hominin sites are located in Africa, such a Laetoli and Hadar. Research initially took place in South Africa and sites such as Sterkfontein were discovered. It was conducted by researchers such a Raymond Dart and much of the research was conducted in cave sites and lime quarries. In South Africa such specimens as Australopithecines, noting there is two separate species, a robust form and a gracile form. Whatever the case this clearly suggests that two hominids lived at the same time and thrived in South Africa.
Attention then shifted to East Africa and was primarily conducted by the Leakys. Sites that were identified here consisted of Olduvai and Lake Turkana. The specimens that were discovered here consisted of Homo habilis, Australopithecus boisei, Homo erectus, Homo ergaster, and Australopithecus aethiopicus.
Until recently fossils were only discovered in South and East Africa. However, important discoveries have been made, for example what is possibly the oldest known hominin, Sahelanthropus tchadensis, was discovered in West Africa.
All of this evidence suggests that early hominins evolved in Africa, and mot scholars agree that they didn’t spread out until roughly 2 million years ago, when Homo erectus decided to take a nice long stroll north.
The First Hominins: Current Contenders –Orrorin, Ardipithecus, and Sahelanthropus
It has been suggested that a good contender for the earliest hominin should be 5-8 million years old and located in Africa. There are three reasonable contenders.
Orrorin: dates about 6 million years old, shows evidence for bipedalism, but exhibits apelike dentition. It was discovered in Kenya.
Ardipithecus: was discovered in 4.4 million year old contexts in Ethiopia, However, earlier specimens have been dated to about 5 million years ago. It also exhibits evidence for bipedalism, however retains apelike dentition.
The last contender is Sahelanthropus: discovered in Chad and is estimated to be 6-7 million years old. It has a hominin like facial structure, reduced canines and thick enamel. It is also possible that it was capable (at least to a certain extent) of upright locomotion. However the remainder of its features are apelike, such as a small rounded cranium and brain, much like a chimpanzees.
What all of this suggests is that Hominins were incredibly diverse and that many co-existed with one another.
Bipedalism
Bipedalism and Human Evolution
There are four characteristics that are important to the human condition, bipedalism, increased brain size, change in dental structure, and the development of culture. However, these characteristics developed at different rates. A key marker of early hominins was the ability to perform bipedal locomotion. Therefore, it is important to understand bipedalism in order to understand hominin evolution (pp240).
Bipedalism is interesting because of the form that it takes is unique to hominins. However, it is also tied to the assumption that bipedalism was essential for the development of tool because it freed the hands. But we have discussed other species that make use of tools that are not capable of bipedal locomotion to the extent that hominins were, such as tool using finches and chimpanzees.
Biomechanics of Bipedalism
There are two characteristics that distinguish hominin bipedalism from chimpanzee bipedalism. The first is that chimpanzees are unable to extend their knee joints. The second is that in bipedal locomotion the center of gravity must shift to the supporting leg and in chimpanzees this is not possible, due to femur structure among other things (pp242-243).
There are a number of adaptations that must occur for bipedalism to be possible.
-curved lower spine
-shorter broader pelvis and angled femur
-lengthened lower limbs and enlarged joint surfaces
-extendible knee joint
-a platform foot, which aligns the big toe with the other toes
-a movement of the foramen magnum toward the center of the basicranium
Ecological Context of the Origin of Bipedalism
It is important to understand that bipedalism was a shift from vertical clinging and leaping, to quadrupedalism, to bipedalism. The environmental context would have to be one that made it advantageous to walk upright and to give up brachiation.
Development of ideas on the Origin of Bipedalism
There are various ideas about why bipedalism developed: it allows for greater stamina, improves predator avoidance, increases thermoregulatory efficiency, warning, a shift in diet/ eating habits, the ability to carry things, and aggressive/impressive displays.
Energetics of Bipedalism: possible implication in its Origin
The development of bipedalism may be linked to changing environments and the availability of resources. Bipedalism is more energy efficient; it allows the hominin to make the most efficient use of their food resources. This type of environmental pressure may explain why hominins developed bipedalism initially. It also allows for a greater distance to be covered by the hominins, which would be necessary if resources were scarce.
Thermoregulation and Bipedalism
Bipedalism reduces the surface area of the body consistently exposed to the sun. This may also be linked to the loss of hair. In an environment where the sun is always beating down it ultimately is advantageous to develop adaptations that aid in regulating body heat.
Time and Energy: the Ecology of a Bipedal Hominin
No adaptation is perfect so in becomes increasingly important to evaluate the cost and benefits of different forms of locomotion. This allows the researcher to understand under which types of conditions bipedalism may be an advantageous adaptation. For example being well adapted for life on the ground makes one less suited for life in the trees.
The major issue that is addressed is not that bipedalism is a uniformly advantageous adaptation, but in what circumstances do the advantages outweigh the disadvantages. This makes it apparent that hominins were at least spending more than half of their time on the ground.
Monday, November 16, 2009
Sunday, November 15, 2009
Chapter 8:Apes, Hominins, and Human: Morphology, Molecules, and Fossils
Chapter 8: Apes, Hominins, and Human: Morphology, Molecules, and Fossils
The topics covered in chapter 8 are: the relationship between living Hominoids and their classification, when did the evolutionary lineages between apes and humans split from one another, and anatomical characteristics of human ancestors shared by both the apes and humans.
There have two prominent ways of classifying Hominoids, one being morphology and the second being molecular. However, different results have emerged from both methods, and our current view of Hominoid relationships is derived from molecular systematics.
Morphology and Molecules: A History of Conflict
Systematics of modern Hominoids is concerned with “which species are evolutionary more closely related to which other species, and how this relationship should be reflected in both species classification” (pp196). The conflicts that arose were basically broken down into two groups: who, of the modern apes, was more closely related to humans and when did the split between human apes occur.
Morphological Interpretations
The question of which of the modern apes was more closely related to humans was not of much concern. It was generally thought that all apes were equally distant relatives of humans. Much of the debate was contingent on different fossil specimens. The Dryopithecus, found in southwest France in 1856, was thought to be ancestral to modern apes such as the gorilla, chimpanzee, and possibly the orangutan. A second fossil was the Palaeosimia, was thought to represent an ancestral form of the orangutan and a third fossil, the Sivapithecus, was thought to represent the origins of the human lineage. These fossils were in turn interpreted to suggest that the human lineage and the ape lineage spilt apart very deep in the past, some researchers suggested 15-20 million years ago and others suggested 30 million years ago.
By the 1960’s there was strong support for two points. The first being fossil apes were ancestral to modern apes. The second the split between the human and ape lineages occurred very deep in the past. These perspectives reinforced the conclusion that the apes were most closely relate to one another and all equally distant relatives of humans.
Molecular Studies
Molecular studies utilize “genetic distances to identify times of divergence between the ape and human lineages” (pp 199). The results of such studies have posited that the time of divergence between apes and humans was, much more recent that the morphologists thought, around 5 million years but not greater than 6 million years.
In contrast to the morphological studies it was also thought that rather than the apes all being closely related to one another and equally distant from humans that the gorilla split from the hominoid lineage first, and then the chimpanzee and human, this in turn suggest that the chimpanzee was more closely related to humans.
What were some of the issues with both morphological and molecular methods and how (if at all were they corrected/explained)? Do you believe that either methods still poses unexplained issues?
A shift in Interpretation: Morphology
With the evidence and interpretations of the molecular techniques, morphological interpretation began to shift closer to the genetic interpretation. This shift occurred for many reasons, one being the importance of molecular data, and the second being new insight into morphological interpretations derived from new data. This new data came in the form of new fossils, cladistics, and re-examining previous data sets.
New fossils came in the form of more complete specimens Sivapithecus, which had possessed more complete facial and cranial regions. These new discoveries made it possible to discern a connection between Sivapithecus, an early hominin, and Ramapithicus, ancestral to the orangutan. This led the morphologists to put the split between apes and hominids closer to 5 million years, like the molecular biologists.
The use of cladistic analyses allowed morphologists to examine attributes and determine relationships between humans and apes. This led them to change their previous view of the relationship between humans and apes.
This in turn, prompted analysis to previous data sets and characteristics previously thought to primitive, such as cranial and dental traits, are in fact derived.
Nature of the Hominin Ancestor
Based on analyses and fossils it is possible to determine what the first hominin may have looked like, when they appeared, and where they appeared.
The close relationship between African apes and humans suggests that the earliest hominin may have inhabited a climate much like the African apes presently do, or in other words be “broadly equatorial” (pp 208). Molecular and fossil evidence suggests that the ancestor should have appeared at some point in the later Miocene, or 4-10 million years, but probably much closer to 5-7 million years.
The appearance of the last common ancestor of apes and humans is probably generalized, but also more chimplike. The size would most likely fall between the gibbon and the chimpanzee. The ancestor would have been primarily arboreal, but incorporated bipedalism into posture and movement. It would also have lacked the skeletal features associated with knuckle walking and would possess large cheek teeth covered with a thick coat of enamel.
However, there is no consensus. For example, Pilbeam suggests that because humans and chimps are so closely related that the ancestral form would posses structures or knuckle walking, and thin enamel. However, the hominin lineage lost these features due to bipedal locomotion and a change in diet.
Classification of Hominoids
There are two issues that affect the classification of hominoids. The first is that traditional/ Linnaean classification reflected the anatomists’ interpretations, which tended to reflect great differences between the apes and humans. This method does not reflect genealogy, which is now the accepted method by researchers. The second is that there is a poor fit of genetic differentiation and evolutionary change at the phenotypic level, meaning that it is difficult to tie genetic markers, which establish lineages, with physical characteristics.
Evolution of Catarrhines: the Context of Hominin Origin
Some General Patterns
There are three general patterns that pertain to Catarrhine evolution. The first is: the geographic distribution of fossil Catarrhines does not coincide with areas where Catarrhines are most abundant today. The second is old world monkeys are more numerous and abundant than apes. The third is that early apes were not primitive versions of modern apes (pp213).
Early Anthropoids
Algeripithecus minutus is a 50 million year old species that may be, however it is uncertain, the earliest known anthropoid. It exhibits cranial characteristics of an anthropoid, but other than that it is rather primitive. However, the Catopithecus browni is the earliest undisputed specimen, about 37 million years old, and it is defined as an anthropoid based on cranial and dental characteristics.
The Earliest Hominoids
Hominoid fossils that date to the Miocene are spread throughout Africa and Eurasia. However, the earliest species known is Preconsul (roughly 22 million years old) were discovered in Africa, indicating that Africa is the most likely location for the clade to have originated. Proconsul is thought to represent the earliest hominoid based on cranial and dental features (large relative brain size and increased surface area of molars/broadening of incisors). However, Preconsul displays a number of ape and monkey traits, such as no tail but monkeylike locomotion.
Preconsul is the earliest known hominoid species and is thought to represent the most basal of the primitive apes. Taking this into consideration:
An interesting note is that Preconsul possessed an opposable thumb, which both apes and monkeys lack. In this situation would the thumb represent a primitive trait retained by humans and not by apes and monkeys, or would it represent a primitive trait that humans re-acquired?
Later Hominoids
Around 17 million years ago hominoid fossils begin to appear on continents other than Africa, such as Asia and Europe. However, the forms that appear outside of Africa possess more modern features, but can still be reasonably linked to the apes.
The best known example of these hominoids is the Sivapithecus, possessing orangutan like characteristics.
Where are the Monkeys
Attention has not been focused on the Monkeys because they were not abundant in the fossil record, an indication that the ratio of monkeys to apes has reversed in present times.
Three approaches to Hominin Origins
The first is genetics suggesting that African apes and Humans are closely related. The second is phenotypes of humans and other apes clearly indicate that humans are great apes. The third is that the fossil record and the climatic context show that hominoids evolved during the Miocene primarily in Africa and then spread across Europe and Asia.
The topics covered in chapter 8 are: the relationship between living Hominoids and their classification, when did the evolutionary lineages between apes and humans split from one another, and anatomical characteristics of human ancestors shared by both the apes and humans.
There have two prominent ways of classifying Hominoids, one being morphology and the second being molecular. However, different results have emerged from both methods, and our current view of Hominoid relationships is derived from molecular systematics.
Morphology and Molecules: A History of Conflict
Systematics of modern Hominoids is concerned with “which species are evolutionary more closely related to which other species, and how this relationship should be reflected in both species classification” (pp196). The conflicts that arose were basically broken down into two groups: who, of the modern apes, was more closely related to humans and when did the split between human apes occur.
Morphological Interpretations
The question of which of the modern apes was more closely related to humans was not of much concern. It was generally thought that all apes were equally distant relatives of humans. Much of the debate was contingent on different fossil specimens. The Dryopithecus, found in southwest France in 1856, was thought to be ancestral to modern apes such as the gorilla, chimpanzee, and possibly the orangutan. A second fossil was the Palaeosimia, was thought to represent an ancestral form of the orangutan and a third fossil, the Sivapithecus, was thought to represent the origins of the human lineage. These fossils were in turn interpreted to suggest that the human lineage and the ape lineage spilt apart very deep in the past, some researchers suggested 15-20 million years ago and others suggested 30 million years ago.
By the 1960’s there was strong support for two points. The first being fossil apes were ancestral to modern apes. The second the split between the human and ape lineages occurred very deep in the past. These perspectives reinforced the conclusion that the apes were most closely relate to one another and all equally distant relatives of humans.
Molecular Studies
Molecular studies utilize “genetic distances to identify times of divergence between the ape and human lineages” (pp 199). The results of such studies have posited that the time of divergence between apes and humans was, much more recent that the morphologists thought, around 5 million years but not greater than 6 million years.
In contrast to the morphological studies it was also thought that rather than the apes all being closely related to one another and equally distant from humans that the gorilla split from the hominoid lineage first, and then the chimpanzee and human, this in turn suggest that the chimpanzee was more closely related to humans.
What were some of the issues with both morphological and molecular methods and how (if at all were they corrected/explained)? Do you believe that either methods still poses unexplained issues?
A shift in Interpretation: Morphology
With the evidence and interpretations of the molecular techniques, morphological interpretation began to shift closer to the genetic interpretation. This shift occurred for many reasons, one being the importance of molecular data, and the second being new insight into morphological interpretations derived from new data. This new data came in the form of new fossils, cladistics, and re-examining previous data sets.
New fossils came in the form of more complete specimens Sivapithecus, which had possessed more complete facial and cranial regions. These new discoveries made it possible to discern a connection between Sivapithecus, an early hominin, and Ramapithicus, ancestral to the orangutan. This led the morphologists to put the split between apes and hominids closer to 5 million years, like the molecular biologists.
The use of cladistic analyses allowed morphologists to examine attributes and determine relationships between humans and apes. This led them to change their previous view of the relationship between humans and apes.
This in turn, prompted analysis to previous data sets and characteristics previously thought to primitive, such as cranial and dental traits, are in fact derived.
Nature of the Hominin Ancestor
Based on analyses and fossils it is possible to determine what the first hominin may have looked like, when they appeared, and where they appeared.
The close relationship between African apes and humans suggests that the earliest hominin may have inhabited a climate much like the African apes presently do, or in other words be “broadly equatorial” (pp 208). Molecular and fossil evidence suggests that the ancestor should have appeared at some point in the later Miocene, or 4-10 million years, but probably much closer to 5-7 million years.
The appearance of the last common ancestor of apes and humans is probably generalized, but also more chimplike. The size would most likely fall between the gibbon and the chimpanzee. The ancestor would have been primarily arboreal, but incorporated bipedalism into posture and movement. It would also have lacked the skeletal features associated with knuckle walking and would possess large cheek teeth covered with a thick coat of enamel.
However, there is no consensus. For example, Pilbeam suggests that because humans and chimps are so closely related that the ancestral form would posses structures or knuckle walking, and thin enamel. However, the hominin lineage lost these features due to bipedal locomotion and a change in diet.
Classification of Hominoids
There are two issues that affect the classification of hominoids. The first is that traditional/ Linnaean classification reflected the anatomists’ interpretations, which tended to reflect great differences between the apes and humans. This method does not reflect genealogy, which is now the accepted method by researchers. The second is that there is a poor fit of genetic differentiation and evolutionary change at the phenotypic level, meaning that it is difficult to tie genetic markers, which establish lineages, with physical characteristics.
Evolution of Catarrhines: the Context of Hominin Origin
Some General Patterns
There are three general patterns that pertain to Catarrhine evolution. The first is: the geographic distribution of fossil Catarrhines does not coincide with areas where Catarrhines are most abundant today. The second is old world monkeys are more numerous and abundant than apes. The third is that early apes were not primitive versions of modern apes (pp213).
Early Anthropoids
Algeripithecus minutus is a 50 million year old species that may be, however it is uncertain, the earliest known anthropoid. It exhibits cranial characteristics of an anthropoid, but other than that it is rather primitive. However, the Catopithecus browni is the earliest undisputed specimen, about 37 million years old, and it is defined as an anthropoid based on cranial and dental characteristics.
The Earliest Hominoids
Hominoid fossils that date to the Miocene are spread throughout Africa and Eurasia. However, the earliest species known is Preconsul (roughly 22 million years old) were discovered in Africa, indicating that Africa is the most likely location for the clade to have originated. Proconsul is thought to represent the earliest hominoid based on cranial and dental features (large relative brain size and increased surface area of molars/broadening of incisors). However, Preconsul displays a number of ape and monkey traits, such as no tail but monkeylike locomotion.
Preconsul is the earliest known hominoid species and is thought to represent the most basal of the primitive apes. Taking this into consideration:
An interesting note is that Preconsul possessed an opposable thumb, which both apes and monkeys lack. In this situation would the thumb represent a primitive trait retained by humans and not by apes and monkeys, or would it represent a primitive trait that humans re-acquired?
Later Hominoids
Around 17 million years ago hominoid fossils begin to appear on continents other than Africa, such as Asia and Europe. However, the forms that appear outside of Africa possess more modern features, but can still be reasonably linked to the apes.
The best known example of these hominoids is the Sivapithecus, possessing orangutan like characteristics.
Where are the Monkeys
Attention has not been focused on the Monkeys because they were not abundant in the fossil record, an indication that the ratio of monkeys to apes has reversed in present times.
Three approaches to Hominin Origins
The first is genetics suggesting that African apes and Humans are closely related. The second is phenotypes of humans and other apes clearly indicate that humans are great apes. The third is that the fossil record and the climatic context show that hominoids evolved during the Miocene primarily in Africa and then spread across Europe and Asia.
Tuesday, November 10, 2009
The Framework of Human Evolution – Part Deux
Chapter 5 - The Systematic Context: From Linnaeus to Exons
Systematics involves the studying of the diversity of life by examining the evolutionary relationships between taxa, a term that can be used to describe any ‘level’ of classification, in an effort to reconstruct their unique evolutionary histories. Linnaeus invented the modern system of classification in 1758 based on anatomical characters, but predictably the field has grown rapidly over the last couple of centuries and now includes complex statistical formulas processed by computers as well as genetic evidence. There are essentially two schools of systematics: phenetics and cladistics. Pheneticists examine as many features as possible, the more features measured the more objective the study, and use statistical analysis to evaluate overall similarity and difference between taxa. Proponents of cladistics, or phylogenetic systematics, deem traits either ancestral or derived and reconstruct evolutionary relationships based on that determination. Hardliners on both sides of the argument claim superiority for their philosophy with cladists arguing that they study the only true evolutionary path and pheneticists claiming pure objectivity and a repeatable process.
An essential component to both philosophies is accurately defining homologies, or homologues, referring to similarities between characteristics of organisms resulting from common ancestry. A very common example of a homology is the morphology of forelimbs in humans, dogs, birds and whales (illustrated above). Cladists claim that their analysis is more precise because they exclusively look at homologous traits whereas pheneticists statistically analyze as many traits as possible without speculating on what might be a derived character. Thus phenetics is not particularly helpful in determining common ancestry, but it provides a more complete estimation in similarity of characteristics between taxa.
More on cladistics-The book provides ample explanation about how cladistics is done in practice and Dr. Anemone drew an exercise on the board a few weeks ago in class illustrating this process.
Molecular research has proved a very productive part of research on human evolution. It was this type of study that determined that humans evolved from our common ancestor of apes closer to 5 mya as opposed to 15-30 mya as previously thought (see figure below). Molecular systematics is, however, not seen as the sole solution to understanding hominin evolution anymore. The specifics of mutation and the varying degree of gene susceptibility according to type have proved elusive to researchers. The view of a single molecular clock has been replaced by the idea that individual gene types each having their own clock ticking at different rates. Both molecular and morphological analyses have a place in reconstructing the path of human evolution and are best used in conjunction with one another rather than competing against one another in search of legitimacy.
Questions:
-Which method (cladistics or phenetics), solely based off of what we have read up to this point, offers the best technique to help explain human evolution? Why?
-Molecular research has a very real impact on the field. In the practice of gorilla conservation molecular studies are employed to estimate similarity between groups and greatly influences conservation practices. Based on the evidence presented in this chapter, how much of weight should be given to molecular analyses be allotted given that it seems the more we think we know the less we actually do?
Chapter 6 – Human Evolution in Comparative Perspective
It is essential that humans are viewed in comparison to other animals in order to discern what is unique to us as a species. This chapter focuses on this type of inquiry and its two basic elements: that we share synapomorphies with other primates and rules govern attributes such as energy, size, and shape in biological systems (126).
Recent trends in human evolution include the loss of robusticity, decreased brain size, size of jaws and teeth and overall stature. The loss of robusticity is explained by the increase in technology, lessening the reliance on brute strength. Nutritional stress is viewed as the primary factor in the decrease stature in humans. This type of stress has been directly related to the increase in size of human populations that created a shortage of resources. Body-size reduction has also occurred in many other animal populations during the same period as humans and is attributed to the increase in global temperature at the end of the Pleistocene.
Questions:
-How will humans evolve next given current environmental pressures keeping in mind the contraints and patterns discussed?
Chapter 7 – Reconstructing Behavior
There is a great variety of social organization found just within the apes. Gibbons are monogamous, orangutans practice “exploded” unimale polygyny, gorillas practice a more tight-knit form of unimale polygyny and chimps practice multimale polygyny. Each species must be examined within their specific evolutionary contexts in order to determine the cause of their social organization, but there are overarching explanations out there. Richard Wrangham claims that selection pressure on female behavior determine the effect of ecology on groups (168). In this view, if resources are patchy then females tend to forage alone and where resources are dense matrilocal, or female kin-bonded, social organization evolves. The high energetic cost of reproduction and postnatal care is why females influence social organization more than males. Sexual dimorphism can also be explained by social organization because the prevalence of male-male competition would select for larger males. Some researchers, like Robert Martin, suggest that science should look towards the possibility that the shrinking of females, instead of the increase in the size of males, as an explanation for sexual dimorphism
Questions:
-Which should be given more weight: comparative analysis between taxa that share similar anatomical characteristics (humans and apes) or those that share(d) similar ecological conditions (scavenging humans and hyenas)?
-How might life-history characteristics among current human populations change provided that our lives remain relatively consistent with the present over the next couple hundred of thousand years?
Systematics involves the studying of the diversity of life by examining the evolutionary relationships between taxa, a term that can be used to describe any ‘level’ of classification, in an effort to reconstruct their unique evolutionary histories. Linnaeus invented the modern system of classification in 1758 based on anatomical characters, but predictably the field has grown rapidly over the last couple of centuries and now includes complex statistical formulas processed by computers as well as genetic evidence. There are essentially two schools of systematics: phenetics and cladistics. Pheneticists examine as many features as possible, the more features measured the more objective the study, and use statistical analysis to evaluate overall similarity and difference between taxa. Proponents of cladistics, or phylogenetic systematics, deem traits either ancestral or derived and reconstruct evolutionary relationships based on that determination. Hardliners on both sides of the argument claim superiority for their philosophy with cladists arguing that they study the only true evolutionary path and pheneticists claiming pure objectivity and a repeatable process.
Homologies
An essential component to both philosophies is accurately defining homologies, or homologues, referring to similarities between characteristics of organisms resulting from common ancestry. A very common example of a homology is the morphology of forelimbs in humans, dogs, birds and whales (illustrated above). Cladists claim that their analysis is more precise because they exclusively look at homologous traits whereas pheneticists statistically analyze as many traits as possible without speculating on what might be a derived character. Thus phenetics is not particularly helpful in determining common ancestry, but it provides a more complete estimation in similarity of characteristics between taxa.Cladistics
Understanding several key terms are necessary to discuss cladistics. Primitive characters, those inherited from ancestors, are also known as plesiomorphies. Derived characters, those unique to the taxa being studied, are also known as apomorphies. A clade is defined by several taxa sharing a derived trait and, because that shared trait unites those taxa, the trait itself is dubbed synapomorphic. If a trait is only found in a single taxon, then that trait is dubbed autamorphic. These are all character/taxon-specific traits which are applied several taxa to group them into monophyletic, paraphyletic and polyphyletic groups. Cladists only accept monophyletic groups, or clades, which are groups where all taxa shared derived characters that emerge from a common ancestor. Clades are the only natural groups because they alone mirror true phylogeny.More on cladistics-The book provides ample explanation about how cladistics is done in practice and Dr. Anemone drew an exercise on the board a few weeks ago in class illustrating this process.
Molecular Evidence
Since the 1980s this approach has been of increasing popularity and influence in evolutionary studies. This increase is due to the ever-increasing amount of molecular data (i.e. genome projects), the development of analysis techniques and the power of modern computers to conduct the analysis. In addition to DNA sequence-based research, analysis of proteins and DNA hybridization (comparison of genomes between species) is also common. Initially molecular research was seen as superior to morphology-based studies because genes were seen as the historical record of evolutionary change (provided we can learn the language it is written in) and that it was seen as immune to convergence by being selectively neutral (most changes in code not being selected for or against).Molecular research has proved a very productive part of research on human evolution. It was this type of study that determined that humans evolved from our common ancestor of apes closer to 5 mya as opposed to 15-30 mya as previously thought (see figure below). Molecular systematics is, however, not seen as the sole solution to understanding hominin evolution anymore. The specifics of mutation and the varying degree of gene susceptibility according to type have proved elusive to researchers. The view of a single molecular clock has been replaced by the idea that individual gene types each having their own clock ticking at different rates. Both molecular and morphological analyses have a place in reconstructing the path of human evolution and are best used in conjunction with one another rather than competing against one another in search of legitimacy.
Questions:
-Which method (cladistics or phenetics), solely based off of what we have read up to this point, offers the best technique to help explain human evolution? Why?
-Molecular research has a very real impact on the field. In the practice of gorilla conservation molecular studies are employed to estimate similarity between groups and greatly influences conservation practices. Based on the evidence presented in this chapter, how much of weight should be given to molecular analyses be allotted given that it seems the more we think we know the less we actually do?
Chapter 6 – Human Evolution in Comparative Perspective
It is essential that humans are viewed in comparison to other animals in order to discern what is unique to us as a species. This chapter focuses on this type of inquiry and its two basic elements: that we share synapomorphies with other primates and rules govern attributes such as energy, size, and shape in biological systems (126).
Primate Heritage
When examining primates, or any other taxa of animals, it is important to remember that each group inherits a basic set of anatomical and behavioral characteristics by which that group is recognized, but that each species is also unique due to its specific (no pun intended) evolutionary path. Primates come in four main types: prosimians, New World monkeys (NWM), Old World monkeys (OWM) and hominoids (apes and humans). Modern classification places tarsiers closer to anthropoids than prosimians, but this aside the general view of primate taxonomy has been rather consistent. Primates are defined by common characteristics, such as grasping hands, hind-limb dominated locomotion, stereoscopic vision, encephalization, and relatively slow reproductive rate in comparison to other mammals. Three main theories postulating the reasons behind the success of these characteristics, and thus primates in general, exist. The arboreal theory, put forth in the early 1900s, was the first to emerge. It claims that life in the trees emphasized the need for nails instead of claws, grasping hands and increase reliance on vision for locomotion in branches. The visual-predation hypothesis followed claiming that the decreased reliance on olfaction and increased reliance on vision while searching and capturing prey allowed for the success of primate characteristics associated with this activity (close-set eyes, grasping extremities, reduced claws, etc). The third theory is that primate radiation was in sync with angiosperm (flowering plants) radiation. The ability to locate and feed on flowering plants would again allow for the success of organisms having primate characteristics. There are problems, however, with all of these theories. Many arboreal animals do not possess primate characteristics and are very successful, early primates were insectivores and research shows that insectivores rely more on hearing than sight, and the timing of angiosperm and primate radiation does not exactly match up. Most likely, it is a combination of all of these along with others that we have not thought of yet that explain the success of primates. Aside from the specifics of the tale of primate success, a constant pattern of increased brain size, intelligence, behavioral flexibility and social complexity is clearly visible in primate evolution. Humans should be seen as merely continuing this trend, rather than traits specific to humans being viewed as novel.The Comparative Perspective
As stated in the introduction for this chapter, uniqueness can only be recognized when comparing one organism to another. A less anthropocentric perspective has allowed for science to progress successfully in this area. From this area we have been able to discover similiarities along with illustrating uniqueness, but it has been proven that both plesiamorphies and anapomorphies look similar when using this technique. Further progress has been made through models that take this into account.Bodies, Size, and Shape
The size and shape of bodies is directly related to an organism’s adaptation to its environment. Climate, for instance, is the underlying factor for surface area/mass ratio as stated in Bergmann and Allen’s rules. Variation in size between populations reflects the evolution of solutions for balancing heat production and dissipation at different latitudes. Humans living in colder climates tend to have larger mass and less surface area when compared to populations living in more temperate climates. Even pygmies, sometimes seen as anomalies to this trend, comply as they are typically found in humid forests where it would be beneficial to reduce one’s volume (decrease size) to lessen the amount of heat generated by the body. Some population migration patterns, like that of the Pecos Pueblo Amerindians, complicate this view because of their slow evolution away from large body width. With respect to human origins, many anthropologists believe that AMH evolved in Africa and radiated out of the continent. This idea that tall, long-limbed people entered lands more conducive to a stouter, robust build is called the climatic hypothesis. A competing hypothesis is the mobility hypothesis that holds early modern Europeans outcompeted Neanderthals because of their long stride length allowing for covering more territory for foraging.Recent trends in human evolution include the loss of robusticity, decreased brain size, size of jaws and teeth and overall stature. The loss of robusticity is explained by the increase in technology, lessening the reliance on brute strength. Nutritional stress is viewed as the primary factor in the decrease stature in humans. This type of stress has been directly related to the increase in size of human populations that created a shortage of resources. Body-size reduction has also occurred in many other animal populations during the same period as humans and is attributed to the increase in global temperature at the end of the Pleistocene.
Bodies, Brains, and Energy
The size of brain and bodies, along with the energy requirements associated with that size, greatly impact the individual life-history of animals. Reproduction requires so much investment that animals have come up with strategies that maximize their Darwinian success. The r-K model offers insight into this matter. It states that the growth of a population is determined by two things: its fecundity and the availability of resources. “r-selected” species have high reproductive and high mortality rates. This maximizes reproductive success in unstable, unpredictable environments. “K-selected” species, on the other hand, have few high-quality offspring indicative of living among limited resources resulting in intergroup competition, thus more parental investment. Overall, primates are large-bodied mammals and this comes with several benefits. For hominins this include a broad diet, large day and home-ranges, high mobility, increased sociality, and enhanced encephalization becoming energetically possible.Questions:
-How will humans evolve next given current environmental pressures keeping in mind the contraints and patterns discussed?
Chapter 7 – Reconstructing Behavior
Bodies, Behavior and Social Structure
The importance of sociality in primates cannot be understated and studying social organization is a vital part to understanding early hominin populations. Since none of us were around for early hominin evolution, we have to infer about the social organization of early hominins by examining living primates. A species’ social organization is comprised of the size, composition and activity of a group (164). This chapter examines the causes associated with living in groups as well as the way individuals adapt behaviorally and anatomically to social structures.There is a great variety of social organization found just within the apes. Gibbons are monogamous, orangutans practice “exploded” unimale polygyny, gorillas practice a more tight-knit form of unimale polygyny and chimps practice multimale polygyny. Each species must be examined within their specific evolutionary contexts in order to determine the cause of their social organization, but there are overarching explanations out there. Richard Wrangham claims that selection pressure on female behavior determine the effect of ecology on groups (168). In this view, if resources are patchy then females tend to forage alone and where resources are dense matrilocal, or female kin-bonded, social organization evolves. The high energetic cost of reproduction and postnatal care is why females influence social organization more than males. Sexual dimorphism can also be explained by social organization because the prevalence of male-male competition would select for larger males. Some researchers, like Robert Martin, suggest that science should look towards the possibility that the shrinking of females, instead of the increase in the size of males, as an explanation for sexual dimorphism
Non-human Models of Early Hominin Behavior
The two major goals of using non-human primates as analogues for early hominins are to study what is seen as “the starting point for human evolution” and gain an understanding of primate socioecology in an effort to reconstruct the behavior of extinct hominins (174). This is practiced via three different models. The earliest of the three techniques involves the selection of a specific species that shares characteristics with hominins and try to transfer lessons of their behavior to hominins. Many species of animals have been used in this way for a variety of reasons, including baboons, chimps, lions and even marine mammals. An alternative model is the phylogenetic comparison which examines shared behavioral characteristics of humans and other primates in order to determine what behaviors are derived or ancestral. The behavioral ecology model is the newest of the three techniques and involves the study of how environment can effect social organization, and therefore behavior as well.Jaws and Teeth
Jaws and teeth are extremely important to reconstructing evolutionary paths of hominin species if for no other reason than the fact that they are plentiful in the fossil record (due to their density) relative to all other fossil remains. There are four aspects of hominoid dentition that tell us much about the behavior and life-history of our ancestors. First, the structure of the jaw and the morphology of teeth illustrate an increase in both brain size and a more generalized diet associated with human evolution. Second, eruption patters differ in apes and humans, thus indicating the degree of relatedness between extinct species and AMHs by their age of tooth eruption. Third, enamel thickness increased throughout human evolution with humans having much thicker enamel relative to apes. Finally, toothwear patterns shed light on the dietary patterns of their former owners.Questions:
-Which should be given more weight: comparative analysis between taxa that share similar anatomical characteristics (humans and apes) or those that share(d) similar ecological conditions (scavenging humans and hyenas)?
-How might life-history characteristics among current human populations change provided that our lives remain relatively consistent with the present over the next couple hundred of thousand years?
Sunday, November 8, 2009
Principles of Human Evolution - Part 1
The Growth of the Evolutionary Perspective
In an introduction to the study of human evolution it is important to recognize the concept of continuity. Evolution is a continuous process that connects all living organisms. However, there are obvious gaps which exist, highlighting cases of discontinuity. The disparity between humans and other apes is one example of this. Humans are uniquely advanced, and yet are still products of the evolutionary process. This gap has been acknowledged first by Darwin in 1859 and four years later by Thomas Henry Huxley. After two great intellectual revolutions concerning humans place in the world, Copernicus declaring the earth was not in fact the center of the universe and Darwin’s publication of Origin, there waere palpable changes in conceptions of where humans should find themselves. Once thought to be separate from nature, after these revolutions humans could be viewed as being a part of nature. Early perceptions of these relationships were seen as a Great Chain of Being, a hierarchy of living organisms with humans at the progressive end.
Q: Even after 1859, humans were seen as naturally superior. Why didn’t the theory of evolution remove the ideal of the Great Chain of Being? How did perceptions of progress alter explanations of the inequality of races?
Q: Our textbook urges us to “mind the gap” concerning our place in evolutionary biology. What is meant by this metaphor?
Considering the historical views of human evolution, two principle matters have continued to dominate the debates over the years. One factor is how close humans are to other apes. Some have argued that humans and chimps are very close while others would like to emphasize the greater differences. The other factor involves how far back in time human characteristics go. The latter brings up issues of what makes us more human such as bipedalism and intelligence.
During the 1960’s scientists were prominent believers in the single-species hypothesis, stating that only one species of hominin could exist at any one time therefore publicizing the idea that human evolution was a single linear progression. Arguments placed great emphasis on the importance of culture. Because humans are characterized by exhibition of cultural traits, it would be impossible for more than one species to survive together. This hypothesis was dismissed a decade later given the current discoveries of fossils proving the coexistence of both Homo erectus and Australopithecus boisei. There are now two complex questions still under research: the origin of the human lineage and the origin of human characteristics.
Q: How have other arguments over the relationship between humans and apes changed over the last 150 years?
Despite differences in theoretical approaches, anthropologists have kept four key events in mind for explaining the development of modern humans. These include the origins of terrestriality, bipedality, encephalization, and culture and have been placed in various sequences depending on differing schools of thought. An important element of the evolutionary perspective, no matter the sequence, is the way in which this information is disseminated. According to anthropologist Misia Landau, evolutionary explanations have typically followed a narrative form by telling a hero’s story (as explained in the previous post). This is notably reflective of how scientists can be influenced by their biased worldviews concerning natural relationships and humans.
Q: “What binds together the narrative of the folk tale and the narrative of paleoanthropology is that both are events that occur through time, and so attracts the form of explanation where one event is causally related to another.” Rather than using storytelling, what would make for a better evolutionary explanation?
The Principles of Evolutionary Theory
Though the idea of biological transformation had been introduced prior to the publication of The Origin of Species, Darwin was the one able to back up his theory with extensive documentation and explanation. Since then, the theory of evolution has gone though many changes, while even today scientists debate the details.
Simply put, evolution is change over time, and natural selection (the survival of genes from one generation to the next) is the mechanism for this change. For natural selection to occur four conditions must be met. Organisms must reproduce offspring, resemble their parents through inheritance, exhibit variation within the population, and compete successfully for resources. As natural selection operates there are two possible consequences in the outcome. If natural selection stabilizes by favoring existing conditions then adaptation occurs. “The better fitted an individual is to its environment, then the better adapted it is (31).” In order for survival to take place, an organism must have helpful adaptive traits. Conversely, if natural selection needs to change into a new mutant form, then evolution occurs. Evolution is basically the change in generational gene frequencies.
Despite this simplicity, arguments arise in evolutionary explanation. This may be due to researchers asking different kinds of questions. Typical explanations for evolutionary events may include factors of conditions, causes, constraints, or consequences, the “four C’s of evolution.”
Q: Why are there different types of evolutionary explanation? How does each approach explain evolution differently?
Darwin’s original concepts included descent with modification coupled with natural selection. Demonstrating how natural selection occurred was not fully explained until the 1930’s, however. At this time new theories developed known as Neo-Darwinism, or Modern Synthesis. This model incorporated Mendelian genetics with a fuller understanding of inheritance. In the 1860’s Gregor Mendel discovered the basic workings of genes by experimenting on pea plants. He was able to conclude that physical traits carry genes that are passed down to subsequent generations intact (without blending). It soon became apparent that phenotypes are influenced by several genes depending on which ones are dominant or recessive, though “no simple relationship exists between a mutation and the degree of phenotypic change it might produce (39).”
Q: What are the foundational differences between Darwinism and Neo-Darwinism? How have new understandings of population genetics changed evolutionary theory?
Other aspects of selection also occur. “Where natural selection adapts an organism for survival in its environment, sexual selection adapts it to the needs of obtaining a mate (42).” This can be seen at the individual level as species selfishly compete among themselves in order to reproduce. However, altruism can arguably exist as well when animals are seen to work for others giving up their own chances at mating. Selection is therefore present at the group level allowing for the social group to succeed rather than the individual. Different levels have demonstrated how we have advanced our understandings of the workings of adaptation.
Q: What are other levels of selection seen in nature?
Pattern and Process in Evolution
This chapter addresses modern debates in evolutionary theory, most notably the question of whether natural selection explains all aspects of change or whether there are other possible mechanisms at work. Basically, how do we explain change? In order to study the patterns of change, it is relevant to comprehend speciation. Given the multiple definitions of a species, due to the complexity of explaining continuity over time and the demarcation of where one species starts and the next begins, it is important to know how a new species arises. One explanation is anagenesis, which occurs through evolution of one species slowly over time. A new species arises when the descendants become so different they no longer resemble the original organism. Another possibility is cladogenesis. This occurs when a species becomes isolated and evolves separately on its own in accordance to the environment it is subjected to. Islands, mountain ranges, and oceans are all barriers which may split species. Because smaller populations have less variation, they are susceptible to faster changes. The latter event is known to create adaptive radiation, the branching that occurs after an evolutionary novelty like feathered flight or bipedalism.
The aforementioned Neo-Darwinian theory sees speciation at the micro-level, basically that natural selection is a slow gradual process of change over time. The gap in the fossil record, the fact that few transitional forms have been found, has led to more recent macro-level explanations for change. The punctuated equilibrium theory proposed in part by our favorite paleontologist Steven Jay Gould would disagree with gradualism stating that species remain relatively constant over long periods of time and when change comes it happens very fast. What is of interest within macroevolution theories is the study of trends within groups of species such the increase of brain size during human evolution. Within this theoretical framework lies the concept of species selection; due to static species over time traits must evolve in a direction within the clade and not the individual species. Extinction is most likely to occur for species with unique environments and low adaptation capabilities, and selection could be happening at the group level. All debates about evolutionary patterning are imperative for understanding “the context in which human evolution must be assessed and explained (55).” What is agreed upon is that linear progression did not occur and the tree of life is very bushy for each species.
Q: Would you rather argue for gradualism or punctuated equilibrium?
Another important element when studying evolutionary theory involves looking at what influences change. Three motives have been recognized, the first being inherited factors of a lineage, second concerning the interactions between species and groups (competition), and thirdly the natural environment. The second point, “biotic context” is interesting when it implies that change can exist purely based on behavior.
Q: Can evolution occur without environmental factors? Can you give examples of struggle among groups and within species that could lead to change?
Environment, it can agreed upon, does influence the survival of organisms. Cladogenesis may take place through either topographic or climatic alterations, both of which are effected by plate tectonics. The environment shifts constantly due to the fluidity of the earth’s crust and the plates that it rests upon. Due to this fluctuation landmasses have become isolated along with the plants and animals dependant of its resources. Either organisms evolve or they die out and become extinct. Plate tectonics have been a major justification for the explanation of species’ origins. Because of the barriers they create there are greater chances for the diversity of life. This has led to the habitat hypothesis stating “species’ response to climate change represent the principal engine of evolutionary change (65).” Evolutionary geography models have also changed over time becoming much more complex.
Q: How may climate change and habitat have affected hominin evolution?
Q: According to the Turnover-Pulse hypothesis, because environmental factors are so important, is it possible for a major climatic event to cause change across multiple species?
Another pattern worth pursuing is how much of a role extinction plays in evolution. Now seen as an important part of the process, it tends to be linked with environmental change. After the Cambrian explosion, close to 30 billion species have evolved on earth. With only 30 million in existence today it is clear that extinction is important to study. At one time catastrophism was the popular worldview thinking that “individual events that wiped out all of existing life, setting the stage for new waves of creation (75),” was the reasoning. Charles Lyell, however, argued for uniformitarianism, believing instead that slow forces were at work over long periods of time. Though the latter won out the debates, it is still clear that catastrophes must have occurred given geological evidence (extinction of the dinosaurs). It may be beneficial to view extinction as a combination of bad luck and selection when determining why some species survive and others do not.
Q: What attributes could help a species chance of surviving?
Q: Why should the study of mass extinction be a significant factor in the study of evolution?
The Geological Context
In looking at human evolution most evidence is found in the geological record. Therefore a firm understanding of earth science is also required. In conjunction with this is the need to establish accurate dating methods. Without dates much of what is found is irrelevant in search for answers about our human past. For fossils, direct dating methods on the material itself do not exist and employing other modes for finding out how old something is is possible. Scientists use both relative and absolute dating techniques in this quest, which we have discussed in the previous class.
Human history rests on sources from fossil and archaeological contexts. Taphonomy, which studies the intricacies of burial and fossil formations, tells us that many deposits are difficult to interpret due to multifarious interruptions such as scavenger raids. Typically, the only bones to remain intact are the strongest ones like jawbones and teeth. What is most important is that the remains be buried as soon as possible. This raises the chances that a specimen might be fossilized (transformation into the lithosphere) and discovered later. Taphonomists have identified most remains as a result of shifting water from rivers and lakebeds and have even located bones in ancient caves.
Much debate revolves around whether deposits result from human, animal, or geological activity. Cut marks on bones may imply carnivorous activity, scavenger commotion, trampling from later herds, or stone tool use. However difficult it may be, taphonomic approaches are crucial to understanding environment, diet, and even culture thousands of years ago.
Q: What other examples are there in distinguishing human behavior from animal activity in the fossil and archaeological record?
In an introduction to the study of human evolution it is important to recognize the concept of continuity. Evolution is a continuous process that connects all living organisms. However, there are obvious gaps which exist, highlighting cases of discontinuity. The disparity between humans and other apes is one example of this. Humans are uniquely advanced, and yet are still products of the evolutionary process. This gap has been acknowledged first by Darwin in 1859 and four years later by Thomas Henry Huxley. After two great intellectual revolutions concerning humans place in the world, Copernicus declaring the earth was not in fact the center of the universe and Darwin’s publication of Origin, there waere palpable changes in conceptions of where humans should find themselves. Once thought to be separate from nature, after these revolutions humans could be viewed as being a part of nature. Early perceptions of these relationships were seen as a Great Chain of Being, a hierarchy of living organisms with humans at the progressive end.
Q: Even after 1859, humans were seen as naturally superior. Why didn’t the theory of evolution remove the ideal of the Great Chain of Being? How did perceptions of progress alter explanations of the inequality of races?
Q: Our textbook urges us to “mind the gap” concerning our place in evolutionary biology. What is meant by this metaphor?
Considering the historical views of human evolution, two principle matters have continued to dominate the debates over the years. One factor is how close humans are to other apes. Some have argued that humans and chimps are very close while others would like to emphasize the greater differences. The other factor involves how far back in time human characteristics go. The latter brings up issues of what makes us more human such as bipedalism and intelligence.
During the 1960’s scientists were prominent believers in the single-species hypothesis, stating that only one species of hominin could exist at any one time therefore publicizing the idea that human evolution was a single linear progression. Arguments placed great emphasis on the importance of culture. Because humans are characterized by exhibition of cultural traits, it would be impossible for more than one species to survive together. This hypothesis was dismissed a decade later given the current discoveries of fossils proving the coexistence of both Homo erectus and Australopithecus boisei. There are now two complex questions still under research: the origin of the human lineage and the origin of human characteristics.
Q: How have other arguments over the relationship between humans and apes changed over the last 150 years?
Despite differences in theoretical approaches, anthropologists have kept four key events in mind for explaining the development of modern humans. These include the origins of terrestriality, bipedality, encephalization, and culture and have been placed in various sequences depending on differing schools of thought. An important element of the evolutionary perspective, no matter the sequence, is the way in which this information is disseminated. According to anthropologist Misia Landau, evolutionary explanations have typically followed a narrative form by telling a hero’s story (as explained in the previous post). This is notably reflective of how scientists can be influenced by their biased worldviews concerning natural relationships and humans.
Q: “What binds together the narrative of the folk tale and the narrative of paleoanthropology is that both are events that occur through time, and so attracts the form of explanation where one event is causally related to another.” Rather than using storytelling, what would make for a better evolutionary explanation?
The Principles of Evolutionary Theory
Though the idea of biological transformation had been introduced prior to the publication of The Origin of Species, Darwin was the one able to back up his theory with extensive documentation and explanation. Since then, the theory of evolution has gone though many changes, while even today scientists debate the details.
Simply put, evolution is change over time, and natural selection (the survival of genes from one generation to the next) is the mechanism for this change. For natural selection to occur four conditions must be met. Organisms must reproduce offspring, resemble their parents through inheritance, exhibit variation within the population, and compete successfully for resources. As natural selection operates there are two possible consequences in the outcome. If natural selection stabilizes by favoring existing conditions then adaptation occurs. “The better fitted an individual is to its environment, then the better adapted it is (31).” In order for survival to take place, an organism must have helpful adaptive traits. Conversely, if natural selection needs to change into a new mutant form, then evolution occurs. Evolution is basically the change in generational gene frequencies.
Despite this simplicity, arguments arise in evolutionary explanation. This may be due to researchers asking different kinds of questions. Typical explanations for evolutionary events may include factors of conditions, causes, constraints, or consequences, the “four C’s of evolution.”
Q: Why are there different types of evolutionary explanation? How does each approach explain evolution differently?
Darwin’s original concepts included descent with modification coupled with natural selection. Demonstrating how natural selection occurred was not fully explained until the 1930’s, however. At this time new theories developed known as Neo-Darwinism, or Modern Synthesis. This model incorporated Mendelian genetics with a fuller understanding of inheritance. In the 1860’s Gregor Mendel discovered the basic workings of genes by experimenting on pea plants. He was able to conclude that physical traits carry genes that are passed down to subsequent generations intact (without blending). It soon became apparent that phenotypes are influenced by several genes depending on which ones are dominant or recessive, though “no simple relationship exists between a mutation and the degree of phenotypic change it might produce (39).”
Q: What are the foundational differences between Darwinism and Neo-Darwinism? How have new understandings of population genetics changed evolutionary theory?
Other aspects of selection also occur. “Where natural selection adapts an organism for survival in its environment, sexual selection adapts it to the needs of obtaining a mate (42).” This can be seen at the individual level as species selfishly compete among themselves in order to reproduce. However, altruism can arguably exist as well when animals are seen to work for others giving up their own chances at mating. Selection is therefore present at the group level allowing for the social group to succeed rather than the individual. Different levels have demonstrated how we have advanced our understandings of the workings of adaptation.
Q: What are other levels of selection seen in nature?
Pattern and Process in Evolution
This chapter addresses modern debates in evolutionary theory, most notably the question of whether natural selection explains all aspects of change or whether there are other possible mechanisms at work. Basically, how do we explain change? In order to study the patterns of change, it is relevant to comprehend speciation. Given the multiple definitions of a species, due to the complexity of explaining continuity over time and the demarcation of where one species starts and the next begins, it is important to know how a new species arises. One explanation is anagenesis, which occurs through evolution of one species slowly over time. A new species arises when the descendants become so different they no longer resemble the original organism. Another possibility is cladogenesis. This occurs when a species becomes isolated and evolves separately on its own in accordance to the environment it is subjected to. Islands, mountain ranges, and oceans are all barriers which may split species. Because smaller populations have less variation, they are susceptible to faster changes. The latter event is known to create adaptive radiation, the branching that occurs after an evolutionary novelty like feathered flight or bipedalism.
The aforementioned Neo-Darwinian theory sees speciation at the micro-level, basically that natural selection is a slow gradual process of change over time. The gap in the fossil record, the fact that few transitional forms have been found, has led to more recent macro-level explanations for change. The punctuated equilibrium theory proposed in part by our favorite paleontologist Steven Jay Gould would disagree with gradualism stating that species remain relatively constant over long periods of time and when change comes it happens very fast. What is of interest within macroevolution theories is the study of trends within groups of species such the increase of brain size during human evolution. Within this theoretical framework lies the concept of species selection; due to static species over time traits must evolve in a direction within the clade and not the individual species. Extinction is most likely to occur for species with unique environments and low adaptation capabilities, and selection could be happening at the group level. All debates about evolutionary patterning are imperative for understanding “the context in which human evolution must be assessed and explained (55).” What is agreed upon is that linear progression did not occur and the tree of life is very bushy for each species.
Q: Would you rather argue for gradualism or punctuated equilibrium?
Another important element when studying evolutionary theory involves looking at what influences change. Three motives have been recognized, the first being inherited factors of a lineage, second concerning the interactions between species and groups (competition), and thirdly the natural environment. The second point, “biotic context” is interesting when it implies that change can exist purely based on behavior.
Q: Can evolution occur without environmental factors? Can you give examples of struggle among groups and within species that could lead to change?
Environment, it can agreed upon, does influence the survival of organisms. Cladogenesis may take place through either topographic or climatic alterations, both of which are effected by plate tectonics. The environment shifts constantly due to the fluidity of the earth’s crust and the plates that it rests upon. Due to this fluctuation landmasses have become isolated along with the plants and animals dependant of its resources. Either organisms evolve or they die out and become extinct. Plate tectonics have been a major justification for the explanation of species’ origins. Because of the barriers they create there are greater chances for the diversity of life. This has led to the habitat hypothesis stating “species’ response to climate change represent the principal engine of evolutionary change (65).” Evolutionary geography models have also changed over time becoming much more complex.
Q: How may climate change and habitat have affected hominin evolution?
Q: According to the Turnover-Pulse hypothesis, because environmental factors are so important, is it possible for a major climatic event to cause change across multiple species?
Another pattern worth pursuing is how much of a role extinction plays in evolution. Now seen as an important part of the process, it tends to be linked with environmental change. After the Cambrian explosion, close to 30 billion species have evolved on earth. With only 30 million in existence today it is clear that extinction is important to study. At one time catastrophism was the popular worldview thinking that “individual events that wiped out all of existing life, setting the stage for new waves of creation (75),” was the reasoning. Charles Lyell, however, argued for uniformitarianism, believing instead that slow forces were at work over long periods of time. Though the latter won out the debates, it is still clear that catastrophes must have occurred given geological evidence (extinction of the dinosaurs). It may be beneficial to view extinction as a combination of bad luck and selection when determining why some species survive and others do not.
Q: What attributes could help a species chance of surviving?
Q: Why should the study of mass extinction be a significant factor in the study of evolution?
The Geological Context
In looking at human evolution most evidence is found in the geological record. Therefore a firm understanding of earth science is also required. In conjunction with this is the need to establish accurate dating methods. Without dates much of what is found is irrelevant in search for answers about our human past. For fossils, direct dating methods on the material itself do not exist and employing other modes for finding out how old something is is possible. Scientists use both relative and absolute dating techniques in this quest, which we have discussed in the previous class.
Human history rests on sources from fossil and archaeological contexts. Taphonomy, which studies the intricacies of burial and fossil formations, tells us that many deposits are difficult to interpret due to multifarious interruptions such as scavenger raids. Typically, the only bones to remain intact are the strongest ones like jawbones and teeth. What is most important is that the remains be buried as soon as possible. This raises the chances that a specimen might be fossilized (transformation into the lithosphere) and discovered later. Taphonomists have identified most remains as a result of shifting water from rivers and lakebeds and have even located bones in ancient caves.
Much debate revolves around whether deposits result from human, animal, or geological activity. Cut marks on bones may imply carnivorous activity, scavenger commotion, trampling from later herds, or stone tool use. However difficult it may be, taphonomic approaches are crucial to understanding environment, diet, and even culture thousands of years ago.
Q: What other examples are there in distinguishing human behavior from animal activity in the fossil and archaeological record?
Wednesday, November 4, 2009
Myths, Narratives, and Folk Tales in Human Evolution
Misia Landau's 1991 book Narratives of Human Evolution had a major impact on the way we think about the science of paleoanthropology. She surveyed the early professional literature on human evolution with particular reference to changing ideas and evolutionary scenarios presented to explain the origin of the hominids, and what she found was unexpected and surprising. Most accounts of human origins included the same four events: bipedality, terrestriality, encephalization, and culture. Where these accounts differed was in the order in which they were said to have occurred, and the relative importance accorded them by different authors. At a deeper level, Landau suggested that all of these stories of human evolution followed the same narrative structure in which a protagonist is challenged and eventually triumphs against all odds. Using Vladimir Propp's classic Morphology of the Folk Tale as her guide, Landau persuasively argues for an essential similarity between the hero tale in much of the world's folk literature (as developed by Propp) and the evolutionary stories that professional anthropologists have long told about human origins. We learn that the hero is us.What does it mean to say that anthropologists have been telling stories about human evolution? And in particular, that they have been telling the same story over and over, with the actual details changed from one version to another, but the essential elements of the story being essentially the same? Can we still claim to be doing "science" when what we write even in oiur profressional literature looks like "folk tales"? Let's discuss this in class today.
Monday, November 2, 2009
Critique of The Bell Curve; Three Centuries' Perspectives on Race and Racism
Critique of The Bell Curve
Gould starts his critique of The Bell Curve by stating it “contains no new arguments and presents no compelling data to support its anachronistic social Darwinism” and that it more reflects the “depressing temper of our time” (pg. 367). He is thus attributing the argument put forth in The Bell Curve falls into the same biological deterministic fallacy as his entire book Mismeasure of Man seeks to expose and eradicate.
The first half of Herrnstein and Murray’s book rehashes the 19th century argument of social Darwinism by arguing that intelligence, depicted by a single number through IQ tests, puts groups of people in a hierarchical linear order based on their genetic inheritance of intelligence. Class-based and racially stratified society is ‘scientifically’ normalized by this old logic because of the faith in the objective truth of IQ testing. Thus, it is Lewis M. Terman’s argument modernized and therefore the argument of The Bell Curve fails because its basic premises are false.
The second half of the book then analyzes the “central fallacy in using the substantial heritability of within group IQ … as an explanation for average differences between groups” (pg. 369). Gould is reusing the same argument posed in his book against the belief in difference through irrevocable genetics – this time against Herrnstein and Murray and their ‘pervasive disingenuousness’ of omitting facts, misuse of statistical methodology, and the unwillingness to admit the consequences of their own study.
Disingenuousness of Content:
Gould fights Herrnstein’s assertion that “what we hope will be our contribution to the discussion [of genetically based difference in intelligence] … [is that] The answer doesn’t much matter” (pg. 370) by showing the disingenuousness of such a statement when the known political ramifications in our society has been shown through studies just like this and the historical social response. Therefore, the supposed objective stance by just ‘stating the statistics’ is not just ignorance but complete disingenuousness of content.
Disingenuousness of Argument:
Gould here analyzes the scientism of the supposed statistical truths behind The Bell Curve and reviewers at the time ignorantly suspecting fallacies of argument, but not checking the actual statistics. Gould argues instead how one-dimensional the book actually is because it ignores the history of such a contentious subject. The bulk of the Herrnstein and Murray’s analysis (‘done in one computer-run’ (pg 371)) deals with multiple regression as a statistical technique and National Longitudinal Survey of Youth as the information source. Therefore, Gould argues that reviewers could have picked up on the errors of Herrnstein and Murray if they were not ‘frightened by numbers’ because the fallacies of argument come in two categories: omissions and confusions; and content.
Omissions and Confusions: Gould cites Herrnstein and Murray’s claim that the general factor of intelligence (spearman’s g) has been decided as the first failure of the study, which angers Gould because of how contentious this subject is with the author’s reporting it as a fact. The way they get away with it is by not explaining factor analysis, which leads Gould to ask: “how can authors base an eight-hundred-page book on a claim for the reality of IQ as measuring a genuine, and largely genetic, general cognitive ability – and then hardly mention, either pro or con, the theoretical basis for their certainty?” (pg 372). By using the same argument posed in Chapter 6 of his book, he shows how using factor analysis (and the people that have used factor analysis such as Spearman and Thurstone) is the only way to explain multiple regression, and by obfuscating this analysis they completely miss a central concept that can be refuted.
Secondly, Gould shows how cultural bias through the technical meaning of statistical bias (S-Bias) and vernacular bias (V-Bias), the entirely different concept that causes popular debate. S-bias means, “that the same score, when achieved by members of different groups, predicts the same consequence”, but V-bias is based on popular questioning and interpretation of the S-Bias, which is said not to exist. Therefore, cultural bias comes out of the interpretation of neutral statistics and the social problems it creates are extensive, to say the least.
Content: Gould analyzes how the authors graph their data of IQ and parental socioeconomic status based solely on the form of relationships through plotting only the regression curve without showing the variation around the curve – therefore showing nothing about the strength of the relationship that variation will either support or not support. It is because their relationships are weak, Gould analyzes, that Herrnstein and Murray hide their data – even going so far as to hide the goodness of fit for multiple regressions in Appendix 4 of the book because their relationships are so weak (to which Gould analyzes their correlation coefficients to find very low causal relationships – indeed not a coincidence).
Disingenuousness of Program:
Gould asserts that The Bell Curve is a manifesto of conservative ideology, to which the notion of ‘advocacy above all’ attempts to cover up its massive flaws in data. The second to last chapter proves this by providing a conservative apocalyptic vision of society wherein the lowly intelligent underclass is taken care of by the ‘custodial state’, making the higher class, higher IQ public have to take care of their inferior lower class. The last chapter then is a conservative call for ‘the good old days’ where higher class, higher IQ people have their roles use their high intelligence, while the lower class is used to maintain society through more menial tasks – all covering up the obvious historical inequality of the class-based system for the benefit of appealing to upper-middle class values.
Here, Gould evokes chapter 7 of his book to expose the fallacy of g as a single, innate, but reified ‘thing’ to be the basis for our understanding of intelligence; to which he (quite poetically) adds: “how strange that we would let a single false number divide us, when evolution has united all people in the recency of our common ancestry – thus undergirding with a shared humanity that infinite variety which custom can never stale. E pluribus unum.” (pg. 378)
Questions:
-Gould addresses at length the disingenuousness of Herrnstein and Murray’s argument, to which they simply argue ‘these are the facts, we didn’t make them, we don’t interpret them, we just report them’. How does this get culturally produced? And, what is so dangerous about this?
-Don’t Herrnstein and Murray’s last two chapters refute their central claim of ‘just reporting the facts’?
-Everyone knows the ‘I’m not a racist’ argument of ‘I have a bunch of black friends’. How is this fallacious argument like Herrnstein and Murray’s?
-What are modern examples of biological determinist arguments?
Ghosts of Bell Curves Past:
The second part of Gould’s critique of The Bell Curve deals with the historical nature of the biodeterminist belief in the ordering of the races by intelligence. Gould here analyzes Gobineau’s 19th century writings and the relation to the argument formed by Herrnstein and Murray in 1994. Where Gobineau’s overt racism aligned the fate of civilizations being determined by racial composition, with decline attributed to the ‘dilution of pure stocks by interbreeding’ (pg. 380), the argument posed in The Bell Curve poses the same argument with a different technological and methodological approach in the modern age of factor analysis supporting a priori assumptions. This links Gobinist thought, through the measure of bodies in the late 19th century, to the hereditary studies of IQ testing of the modern era.
Gould then gives us The Mismeasure of Man in a nutshell: that the ‘Gobinist’ version of mental testing that argues for an innate intelligence generalized across human groups relies on four interrelated premises. Any one premise deemed false and the whole scientific enterprise of biological determinism is ruined:
1. Intelligence rests upon a single factor of intellectual capacity, or g.
2. The amount of intelligence of every individual can be reduced to a single number, or IQ.
3. The single number measures an inborn quality of genetic makeup, which is highly heritable from generation to generation.
4. An individual’s IQ is stable, permanent, and subject to little change through social intervention or education.
Therefore, because Herrnstein and Murray commit all of these false premises, Gould’s argument throughout Mismeasure makes The Bell Curve just another example of biological determinism as an extension of a culturally biased Gobinist study.
Gould ends his critique with a 1994 Newsweek article about a Bronx high school committed to providing high educational standards to disadvantaged students. Gould is hopeful but distressed when the writers use the positive statistics that the high school has provided by their programs as defiance to ‘Darwinism’. This shows, much to Gould’s chagrin, how the writer’s misnomer of Darwin (in place of what they think to be ‘biology’ in terms of fixed genetic limits) symbolizes our social ignorance on many levels of the gains in evolutionary biology.
Questions:
- Dealing with the Newsweek article, is misinterpretation and misinformation still a problem for evolutionary biology? Or, have Gould’s arguments been placed in the realm of popular, factual discourse? (This is admittedly a red herring, but I think it brings up some good points.)
Three Centuries’ Perspectives on Race and Racism
Age-Old Fallacies of Thinking and Stinking
The first part of Gould’s article deals with the 17th century writings of the English writer Sir Thomas Browne, who refuted (at length) popular misconceptions of the day, much as science does to expose truths out of popular myth. Particularly, Browne is interested in the common 17th century notion that Jews, as a racial group, stink. Gould uses this example to refer to what he calls ‘surrogacy’, or, how certain popular claims – from Jews stinking to Blacks being unintelligent – act as surrogates for the same kind of fallacious logic. He refers to the form of argument always being the same, being ‘permeated by identical fallacies over the centuries” (pg. 397).
Here he makes the connection to the arguments posed in The Bell Curve of how peoples from African descent on average have less intelligence than every other group in the world. He ties this to the gains in the fields of paleoanthropology and human genetics, where various findings are pointing to the fact that Homo sapiens emerged from Homo erectus in Africa, then spread out to the rest of the world; or the out-of-Africa view. Specifically, Homo sapiens did not migrate out of Africa until 112,000 to 280,000 years ago, with evidence pointing closer to 112,000 years ago. So, non-African racial diversity has happened only over the last 100,000 years or so, with Homo sapiens having lived exclusively in Africa for a much longer time. This is supported by the fact that people of African descent have more genetic variation between each other than the rest of the supposedly ‘non-African world’ has combined.
Racial Geometry
The second part of Gould’s article deals with the 18th century scientist J.F. Blumenbach and his taxonomic system of dividing humans into five groups or ‘varities’: Caucasian, Mongolian, Ethiopian, American, and Malay. These groups were defined by geographic location and appearance and they replaced the four divisions that Blumenbach’s mentor Linnaeus had devised (Americanus, Europeus, Asiaticus, and Afer). The switch by Blumenbach, Gould analyzes, was his attempt to order humans subjectively on putative worth, with Caucasians on top due to their physical beauty. The name ‘Caucasian’ itself derives from Blumenbach’s belief that the mountain range in Russia is where the people are most aesthetically beautiful and therefore where Caucasians originated.
This leads Gould to concede that he does not believe Blumenbach was being overtly racist in his geometric rankings -- in fact he believes Blumenbach to be the least racist and most egalitarian of the enlightenment age – but his taxonomy is based on societal beliefs influencing him at the time. In Gould’s words: “When scientists adopt the myth that theories arise solely from observation, and do not scrutinize the personal and social influences emerging from their own psyches, they not only miss the causes of their changed opinions, but may also fail to comprehend the deep and pervasive mental shift encoded by their own new theory” (pg 406).
Therefore, his model of Homo sapiens separating into different groups ‘degenerating’ from their perfect state of those from the Caucus Mountains to two symmetrical lines of racial categories, must be taken into context of the influence of his time on his own theories (of which is a major theme of Mismeasure) – that way we can see how in books like The Bell Curve how the society influences what is supposed to be scientifically objective, but just a product of the times.
The Moral State of Tahiti – and of Darwin
The last part of Gould’s article explores Darwin’s writings and its reflection of paternalism as popular sentiment at the time of his writing. Gould analyzes Darwin’s first published writing “The Moral State of Tahiti” co-authored with Robert FitzRoy, his colleague on The Beagle. The article was written in response to the Russian explorer Otto von Kotzebue’s argument that Christian missionaries were destroying native cultures by doing more harm than good. Darwin and FitzRoy countered with their paternalistic interpretations of the Tahitian people and how Christianity has made them better people from their savage beginnings.
By today’s standards, this is an ethnocentric, racist argument, but as Gould argues, Darwin was writing from the paternalistic nature of the society that he grew up in. Darwin goes on to write even in his mature years based on the same belief in a “hierarchy of cultural advance, with white Europeans on top and natives of different colors on the bottom” (pg 416). He particularly despised the Fuegians of South America and wrote at length of the superiority of men over women. But, as Gould states “Darwin was a meliorist in the paternalistic tradition, not a believer in biologically fixed and ineradicable inequality” (pg 419). Therefore, because Darwin believed in improvement in mankind, from ‘savagery’ to ‘civilization’, Gould argues that without this belief – no matter how racist, sexist, and ethnocentric his paternalism is by today’s standards – Darwin would have “lost his date with history” (pg 420). In addition, it was his paternalistic morality that led him to be a fervent abolitionist and advocate of human rights, by believing in the equality of man – even if it did mean despising certain racial and ethnic groups – but it goes along with Gould’s argument all along, how society’s beliefs and standards influence our biases and practices.
Gould ends with an anthropological call-to-arms of the pluralistic study of cultural diversity in the face of conservative cynicism of leftist ‘political-correctness’ (finely showcasing his Marxist humanistic influences) in the goal of countering Darwin’s most famous line: “If the misery of our poor be caused not by the laws of nature, but by our institutions, great is our sin” (pg 424).
Questions:
-These three sections of the article deal with Gould’s argument of scientific logic being a product of their times, what are modern examples of this? Or, how is the scientific process dismantling popular logic?
-What do you think of Gould’s argument that Darwin’s British paternalistic thought processes as a rather fortunate timely logic for the creation of evolutionary biology? Where does this place human agency?
Links:
American Psychological Association's response to The Bell Curve: http://www.gifted.uconn.edu/siegle/research/Correlation/Intelligence.pdf
Charles Murray's 2005 article The Inequality Taboo: http://www.bible-researcher.com/murray1.html
Wikipedia Article: http://en.wikipedia.org/wiki/The_Bell_Curve
Wednesday, October 28, 2009
Gould: A Positive Conclusion and Swift Debunking
Gould: A Positive Conclusion and a Swift Debunking
Throughout The Mismeasure of Man, Gould has examined several key contributors to a recurring theme of biological determinism. Gould was able to expose the fallacies, errors, and fraud that key figures in “science” utilized as the basis for their theories on race and intelligence as being something that could be inherited, reified, and ranked. Gould (p.351) suggests that the concept of unilinear progress is not only a determining factor of social rankings; it is also suggestive of an incorrect idea of the development of science. Gould uses the metaphor of science as a barrel of accumulating knowledge to explain how science develops. He indicates that some would view debunking as negative because it would only eject a few rotten apples (bad theories) from this barrel. Gould disagrees by explaining that the barrel is constantly at capacity, and the rotten apple must be discarded in order to create space for better apples. Gould Specifies (p.352):
Scientists do not debunk only to cleanse and purge. They refute older ideas in the light of a different view about the nature of things.
It is this perpetual development, debunking, reinvention, and at times revitalization within science that generates new ideas and theories, but in order for the debunking to have a long-term effect it must, as Gould points out (p.352), utilize more competent biology to remove erroneous ideas rooted in social prejudice. Due to the increase of knowledge about human biology, evolution, and genetics, biological determinism has suffered several defeats in theoretical fundamentals supporting it. Gould (p.352) argues that the significant lack of genetic variation among human populations is one of the primary biological principles for dispelling biological determinism; this variation is a contingent reality in evolutionary history.
Is the human species at a point where we can make arguments of “fact” regarding sciences such as biology, or are we just perpetuating the debunking machine by replacing more rotten apples with better ones? Debunking has been a common occurrence throughout history. Most likely there have been ideas that were discredited without the support of knowledge. What if Mendel’s ideas were tossed out? Would it be inevitable that eventually someone would have discovered inheritance?
On Biology and Human Nature
Humans are inevitably a part of nature. The complex system of organization that makes up the human organism operates on the same principles of life as do other forms. Do we maintain uniqueness if we share our biological systems? Gould (p.354) states that human novelty has had an immense impact upon the earth because of the new kind of evolution, or the adaptation humans have exploited: culture. The brain is where this special and peculiar ability resides. Has cultural evolution been the “smoking gun” of how the species has managed a strangle hold on the world? An Australopithecine might disagree, but a shotgun trumps an Oldowan chopper, right?
All the advancements and transformations have occurred at a higher frequency in the shortest amount of time in history (written or geologic). Gould (p.355) argues that cultural evolution can happen at such an accelerated rate because it operates by the inheritance of acquired traits. Biological evolution occurs at a much slower rate. Another important trait of cultural evolution is that it is reversible where biological evolution is not.
The classical arguments of biological determinism in what we have scrutinized fail as a result of them being founded within products of cultural evolution. In other words, biological determinism has not foundational basis because they are measuring socio-cultural bias and not biological traits. As a result in the advancements in science, the very biological basis of the human species extinguishes the arguments of biological determinism. Gould describes that the inheritance and modification of acquired behavior is more effective than biological evolution in relationship to the human organism. Do you agree with that assumption or has too little time of a grander scale gone by? It is easy to assume that cultural evolution is what allows us to be somehow unique and more advanced than the chimpanzee. Have we developed beyond our means?
Gould (p.357) believes that modern biology has created a model that straddles the claim that biology has nothing to educate us about human behavior and the theory that specific behavioral traits are a result of the selective adaptations that are embedded with our genes. Gould also provides 2 major areas for biological comprehension.The first is in fruitful analogies and the limited use thereof. Gould describes the use of analogies as a means of inferring genetic similarity as one of the most frequent errors of reasoning. Just as a correlation in factor analysis may expose common relationships, but it doesn’t identify and explain the cause.The second is biological potentiality versus biological determinism. Biological potentiality is the concept that underlying generating rules are what perpetuate human behavior and not the deterministic idea that the genetic basis of human nature exists among specific behaviors. Gould (p.359) points out that sociobiologists have made a primary error seeking the genetic basis of human behavior at the wrong level.
Two different arguments have led Gould to determine that broad behavioral ranges occur as a consequence of the evolution and structure of the human brain. The first argument relies on the vast range of human behavior from peaceful to aggressive. Human behavior is malleable based on the context of the situation. Gould (p.361) believes that is likely that natural selection acted to maximize the range of human behavior. The second argument is that the structural design of our brain has led to our increased capacities for human success.
Gould invokes the idea of neoteny to close his chapter. Is flexibility within the human species really the hallmark of human evolution? By retaining a more juvenile capacity to adapt and learn, has the human species found a niche in not evolving? Is the structure of our brain a product of a lengthy biological journey, or is it a rapidly advancing adaptation generated by culture within the biological range of variation? Can culture really act as an agent of change at a level that rivals biology?
Links-
Gould on Human Nature
http://condor.depaul.edu/~mfiddler/hyphen/gould-humanature.htm
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