Part III: Later Hominin Evolution, Part I

Chapter 14: The Origin of Modern Humans: Background and Fossil Evidence

This chapter deals with the evolutionary transition from Homo erectus to Homo sapiens and the scientific arguments to how this transition has occurred. Anthropologists agree on certain anatomical and behavior changes in this transition, namely a decrease in skeletal and dental robusticity, modifications in locomotor functional anatomy, and an increase in cranial volume for anatomy; and the increase in diverse tool technologies, more efficient foraging strategies, more complex social organizations, full development of spoken language, and artistic expression for behavior.

The two extreme viewpoints within paleoanthropology of the transition that took place is that on one side a gradual change within all populations of Homo erectus took place simultaneously, leading to the appearance of Homo sapiens in Africa and Eurasia. On the other side, modern humans have a single African origin that spread out across the old world and replaced non-modern populations. These extreme viewpoints are supported by different anatomical, genetic, and archaeological evidence with the weight of the evidence currently supporting a form of the single-origin model. Chapter 14 covers the anatomical evidence.

Two scenarios exist for the evolution of Homo in explaining how Homo sapiens came into being. In, the “Homo erectus as general ancestor” scenario, Homo as a new grade of hominin was established in Africa about 2 million years ago, and eventually spread itself across the old world. Having this large and widespread population, considerable local variation can be expected that could largely be minor, but certain major adaptations could be transmitted – either thru gene flow or cultural transmission – to homogenize the larger population. Speciation does not occur because of the large amount of minor variations taking place, but the overall homogenous effects for the whole population would serve as the evolutionary change. In this model, major behavioral differences would not be developed due to the homogenization across the larger population through genetic flow and cultural transmission.

The second scenario, “Homo as separate local trajectories” posits that H. ergaster dispersed out of Africa at a later point into relatively small, isolated populations. These populations would be prone to greater differentiation through drift or selection, but also more prone to extinction. This would cause each population to be more prone to form species boundaries and for local evolutionary trajectories to be independently established – recognizing H. erectus and H. ergaster as the result of evolutionary divergence. H. sapiens, then, would evolove from one of these trajectories. In this model, behavioral difference would become very distinct due to local isolation, leading to several modes of hominin behavior being present at all times – the long-term effects of this being a major component of later human evolution.

Competing Hypotheses for Modern Human Origins

The multiregional hypothesis originated in the 1940s from German anatomist Franz Weidenreich. He believed that anatomical diversity evolved from distinctive traits in different geographical regions from the time of H. erectus through modern humans, which he referred to as regional continuity. Recently, Alan Thorne and Milford Wolpoff have built on the multiregional hypothesis to what is now known as multiregional evolution hypothesis, which sees the transformation of H. erectus to H. sapiens as a “balance between the maintenance of distinctive regional traits in anatomy, through local regional adaptation, and the maintenance of a genetically coherent network of populations throughout the Old World, through significant gene flow” (p. 372). For this to be true, three expectations should hold true: anatomically modern humans will appear in the Old World during a similar period, transitional fossils (archaic-modern) should be found in all of the Old world, and in each Old World region, continuity should be apparent for the anatomy of ancient to modern populations.

The single-origin hypothesis dates to the 1960s from Louis Leakey, who believed that Middle Pleistocene hominins from Africa are better models than the H. erectus fossils of Asia, which he believed to be evolutionary dead-ends. Chris Stringer builds on the single-origin model of the replacement of archaic populations by invading modern populations by believing that today’s regional anatomical traits are the result of adaptation and genetic drift locally in the past 100,000 years. For this to be true, four predictions should hold: anatomically modern humans should be found in Africa much earlier than other areas, transitional fossils from archaic-modern should only be found in Africa, traits distinguishing modern geographical populations should show no links to early populations in the same region, and there should be little to no evidence showing hybridization between archaic and early anatomically modern populations.

Chronological Evidence

Specimens of anatomically modern humans from Africa and the Middle East date to be significantly older than those found in the rest of the Old World. The oldest recorded modern human population comes from the Middle Awash region of Ethiopia dating to 130,000 years ago, found by Tim White in 2003, naming the subspecies Homo sapiens idaltu. In the Middle East, Israeli cave sites have yielded specimens dating close to 100,000 years ago although retaining some archaic features. Nevertheless, scientists claim the specimens to be essentially modern. Asian sites have yielded older anatomically modern specimens, but their origin dates are widely argued and rejected, leading most scientists to believe the specimens to be only 60,000 years old. There is therefore a chronological gap that exists of tens of thousands of years between specimens found in the African/Middle Eastern region and those found in the rest of the old world, therefore giving claim to the ‘out of Africa’ hypothesis.

The Question of Regional Continuity

Because the multiregional hypothesis depends on regional continuity, scientists must find proof of such continuity in the fossil record – a contentious subject, to say the least. Figure 14.5 (p. 376) nicely lays out the chronology of anatomically modern humans region by region, which strongly supports the ‘out of Africa’ hypothesis.

- As the authors lay out each argument of each fossil find (pp. 377-391), does this support the argument that scientists are basing their observations of fossil finds

on a priori premises? Does this apply to the lumping vs. splitting debate as well?

The authors state the importance of voices outside of the current debate in interpreting which hypothesis is correct. Both Aiello and F. Clark Howell are cited as siding more with the out of Africa theory, but that no hypothesis yet can completely explain the observed fossil evidence. Further, Marta Lahr’s study of cranial features concludes that no substantial morphological evidence exists to support the multiregional model, as well as Diane Waddle’s matrix correlation tests.

The Place of Neanderthals in Human Evolution

The authors discuss the importance of Neanderthal findings because of the early discovery in the Neander valley in 1856 (three years before the publication of Origin) and the substantiation they gave to the debate of modern humans as evolved animals. Although the argument of Neanderthals being the ‘missing link’ has long been abandoned because of the subsequent findings of older hominin forms, the Neanderthals remain important in the history of paleoanthropology as a ‘test-bed for many ideas about the human evolutionary past’ (p. 395). One such important argument was put forth by Lewis Binford’s analysis that Neanderthals were behaviorally very different from modern humans, and that the contrast between the Middle and Upper Paleolithic shows the change from non-human to human behavior, or the “cultural revolution”. The current view holds that modern humans and Neanderthals diverged at some point within the last half million years and recorded parallel evolutionary histories – making the two groups two separate species, Homo sapiens and Homo neaderthalensis. The genetic evidence of chapter 15 substantiates this theory.

-Does the historical importance placed on studying Neanderthals help show the extent of western-centric bias in the sciences?

Chapter 15: The Origin of Modern Humans: Genetic Evidence

The Impact of Molecular Evolutionary Genetics

Genetic evidence has begun to show just how complex the event of the origin of modern humans really was, and in turn how simple the hypotheses based on fossil evidence really are. Douglas Wallace first studied this in the 1980s by focusing on mitochondrial DNA, inspiring the famous ‘mitochondrial eve’ hypothesis. This posits that all mitochondrial DNA of living humans can be traced back to a single female living in Africa approximately 200,000 years ago. This female would have been in a population of about 10,000 individuals, all relating to the foundation of the modern human population who spread across the old world and replaced all existing archaic species of Homo. This data was deemed inadequate during the 1990s (see p. 405 for a detailed analysis), with genetic work shifting to two pathways: one extending mitochondrial DNA analysis to include other genes (including ones from the nucleus) to determine when and where humans evolved, and the other using mitochondrial DNA to infer population dynamics of early modern humans – both supporting the single-origin ‘out of Africa’ claim.

Mitochondrial DNA is useful for understanding recent evolutionary events for two reasons: first, because it accumulates mutations ten times faster than in nuclear DNA therefore providing more information over the short term; and second, because it is inherited only from the mother, it substantially cuts through the fog that recombination (maternal and paternal) genes create. The evidence collected from mitochondrial DNA supports a recent bottlenecked, single-origin model of the human lineage.

The problem with studying mitochondrial DNA is that it provides a gene history, not a population history. The mitochondrial is just one special gene and scientists now realize the need to study other genes to search for evidence to substantiate evolutionary claims.

Recent Developments

Scientists are now looking at two new types of genetic data, the first being microsatellites which are rapidly evolving short stretches of DNA of two-to-five-nucleotide segments. David Goldstein has used this technique to find a coalescence point of origin of approximately 156,000 years ago. The second is Alu elements, which are sequences of DNA approximately 300 base pairs long that are inserted in large numbers over the nuclear genome. Once these are inserted, they are never removed and therefore remain immune to homoplastic changes. A recent multi-authored analysis has resulted in a coalescence time of 102,000 years.

Another study focuses on the fact that because mitochondrial DNA helps give the history of women, the Y sex chromosome will help give the history of men, because only men possess it. Stanford University scientists are using the Y chromosome to obtain a coalescence of between 100,000 and 150,000 years, with a pattern showing greater African diversity than the rest of the world’s modern populations.

The importance of coalescence times in different genetic studies shows how some genetic systems have older patterns of diversity, even if there was a ‘harsh population bottleneck’ of 150,000 years ago that is supported by this evidence. Therefore, studying the complexity of different genes and their coalescence times will help broaden our understanding of our overall population history.

This has led to the study of the bottlenecking of modern human populations over history, with the severe reduction coming from different environmental events followed by the explosion in numbers of individuals in the population. Certain hypotheses have been put forth supported by genetic evidence, including the Garden of Eden hypothesis (figure 15.14, p. 415), which posits that humans fragmented within Africa forming distinct genetic populations. Subsequent population bottlenecks within Africa led to ‘proto-‘ European, African, and Asian populations that then began to spread across the old world. The authors deem this argument to be very weak, but nevertheless one of the many hypotheses developed in the out of Africa model. Figure 15.16 (p. 419) further illustrates the evidence of the history of bottlenecking in human evolution and the relation between genetics and population dynamics – all supporting the out of Africa hypothesis.

-As the field of molecular genetics expands in trying to explain the origin of modern humans, what can be learned from the past in forming sound hypotheses?

Chapter 16: The Origin of Modern Humans: Archeology, Behavior, and Evolutionary Process

This chapter explores the archaeological evidence that would help support the claim that modern human behavior would start first in Africa and spread out to the rest of the old world. This archaeological evidence should substantiate the link between behavior and biology in the history of modern human populations and whether biology led to behavior or vice versa. However, a gap exists in these findings because the small amount of sites in Africa (only about a dozen) in comparison with other sites (SW France, for example with 100 sites, but 100 times smaller than the area in East Africa). This can lead to misinterpretations (Eurocentric, specifically) because of the lack of evidence in the archaeological record, so much work needs to be done to further the out of Africa hypothesis from the archaeological and behavioral standpoint.

The dates in question are the Middle Stone Age and Late Stone Age in Africa -- 300,000 to 30,000 years and 30,000 and 10,000 years, respectively. The equivalent stages Europe, Asia, and North Africa are known as the Middle Palolithic and Upper Palolithic, and all deal with the tool assemblages of specifically anatomically modern human populations first explored in Chapter 12. Figure 16.7 (p. 430) nicely summarizes the findings of these stages in different areas of the old world and the tie between the origin of Homo sapiens, the environment, and complex behaviors.

Regional Patterns in the Archeology

European evidence: The transition in Europe is known as the Upper Paleolithic revolution, which coincides with the first appearance of modern humans to the region that carry the cultural traditions that are known as Aurignacian. This happened about 40,000 years ago, according to radiocarbon evidence in northern Spain and it includes blade-based technology and the use of bone, ivory, and antler for points as well as body ornamentation. As the upper Paleolithic progressed, so did temporal and spatial variability of style and the foundations of cultural traditions as we know it today for the Aurignacian.

Asian evidence: The Middle East provides evidence as a natural migration route between Africa and the east and evidence exists from at least 200,000 to 50,000 years ago of Neanderthal, early modern, and other hominin populations. The scarcity of sites in Asia make it difficult for scientists to interpret behavior and tool use, but evidence does suggest significant differences between the east and the west of the continent – further evidence for the out of Africa hypothesis, with the possibility of multiple dispersals of hominin populations.

African evidence: Sub-Saharan Africa should hold the evidence for the evolution of modern human behavior for the out of Africa hypothesis to hold true. This is important not only for finding the earliest date of modern human tool-using behavior, but also include transitional steps in line with dispersals to other parts of the world. In sum, archeological evidence should mirror scientific presuppositions. Figure 16.11 (p. 439) shows the evidence collected towards explaining ‘modern’ African behavior – but the archeological record is very sparse in comparison to Europe, leading scientists to find very little early symbolic behavior in contrast to European findings. This is because of, as Alison Brooks (and the authors) argues, the unfavorable conditions for preservation in Africa and the little amount of sites actually investigated.

-Although the anatomical and genetic evidence is strong for the out of Africa hypothesis, does the lack of archaeological evidence give credence to the multiregional hypothesis believers? Is it fair to assume past African behavior although the archaeological evidence is by no means complete?

Toward an Integrated Model of Modern Human Origins

The authors argue for a ‘multiple-event, multiple-dispersal’ model to build on the out of Africa hypothesis. This is based on a few interrelated premises supported by evidence presented thus far:

- All living humans are descended from a relatively small population from Africa (in all probability) dated to approximately 150,000 years ago.

- Hominins outside that population, be they archaic or modern, have not contributed significantly in genotype or phenotype to the modern population – all consistent with the notion that the modern population from Africa colonized and replaced all other populations.

- The ‘origins’ of modern humans are not based on a single event, but rather spread over the last 200,000 years towards the development of anatomical modernity in Africa.

- Multiple dispersals explain the spread of modern human populations around the world.

- Modern humans share their evolutionary origins in archeological terms of the ‘Mode 3 industries of Africa’ with the Neanderthals. Behavior is shifted in cultural terms rather than biological or genetic.

- Not all archaic hominins are the same.

These premises are all related to the ‘principles of evolution’ outlined by the authors (p. 444): the importance of geography, the role of the climate, the role of behavior, the importance of microevolutionary processes, and the importance of extinction in explaining all evolutionary process and change.

-The authors discuss the need for complexity in understanding human evolution as opposed to the simplicity that Darwinism offers. Is human evolution that much more complex or are we as susceptible to the same evolutionary processes that affect all of life? Is it possible that our belief in the complexity of our evolutionary history is a reflection of our unique ecological niche as a big brained, socially dependant species? For example, what would Canis familiaris say about its own evolutionary history if it could?

Part II: Chapters 12 and 13

Chapter 12: Behavior and Evolution of Early Hominins

The Archaeology of Stone Tools

Instead of stone tools being studied as the focal point within a system of typologies, or types of types, the study of artifacts within a context of subsistence strategy has become the current trend. Archaeologists study artifacts including chipped stone tools as a method of determining not only individual tool function, but they use their analysis to answer larger methodological questions relating to subsistence practices. One way of determining function is by practicing the methods and techniques that were used to create the original artifact. This type of research is called experimental archaeology. There are 5 modes of defined stone tool assemblages: Mode 1. Oldowan (chopping tool), Mode 2. Acheulean (uniformly flaked bifaces), Mode 3. Prepared Core (Levallois-micro flaking), Mode 4. Blade ( Upper Paleo, Later Stone Age), and Mode 5. Microlith(Mesolithic, small, delicate tools). The different modes of stone tool technology appear at different periods, but often continue to be utilized in later stone tool assemblages. Simple chopping tools of the Mode 1 kit can be found in the archaeological record up until the late historic periods in North America. Tool kits like the Oldowan and the Acheulean have a persisting utility based on their multiple functions and ease of preparation.

The Earliest Known Tools-

At approximately 2.5 mya, the oldest recorded stone tool artifacts appear in the archaeological record. They have been recorded at several sites, but the technology is named after the Oldoway Gorge in Tanzania (Those Leakeys are everywhere). Four categories of stone tools were created from Mary Leakey’s research: tools, utilized pieces, waste, and manuports. It is important to point out that the assemblage variety attributed to the Oldowan are more of a result of opportunistic production (p.312); artifacts tend to blend in one another typologically as a result. Utilized pieces tend to resemble waste, and scraper tools and choppers are often the product of flake production through various types of percussion. Manuports are pieces of rock that have been carried to a site, but have not been modified. They are frequently comprised of materials that could be used as percussion tools or could be percussion flaked into a chopper or scraper. Early hominins may have used a variety of materials such as antler, bone, or wood, but preservation in the archaeologicical record is poor for those material types. The stone tools associated with early hominin use have wear patterns indicating they were used for a range of subsistence activities such as butchering, wood-working, and plant processing (p.315). The broader implication for the Oldowan technology is nothing short of one of the most significant technological revolutions that may have contributed to further encephalization (p.315).

How has the discovery of Homo Floresiensis redefined the correlation between brain size and tool production capabilities since they had a tiny brain yet potentially created advanced stone tools?

The Kanzi Experiment: Oook oook oook!

In addition to the debate that pits Australopithecus against early Homo, a debate exists over whether apes have the physical and cognitive ability to create stone tools. The cognitive demands and physical structure of the arms, wrists, and hands were studied in Kanzi, a captive bonobo. Although Kanzi was able to produce stone tools, the lithic product differed from the Oldowan assemblages. The studies failed to determine if Kanzi’s poorer performance reflected differences in cognitive ability or anatomical constraints (p.317).

A frequent argument resides regarding the identity of the hominin responsible for early stone technology. The two representative and contemporaneous hominins are Homo and Australopithecus. By comparing hand morphology, pro-Australopithecus advocates such as Randall Susman conclude that later robust australopithecines had the manipulative ability based on hand morphology to create stone tools (p.318-319). It is possible that both species were able to produce stone tools and something led to technological expansion in the genus Homo.

Tool technology appears to have expanded, but did not necessarily originate, along a parallel gradient with the brain. What different hypotheses might be able to account for this parallel expansion? What adaptive strategies (e.g., resource intensification, niche exploitation, predation defense, warfare…) would have been well-suited for the implementation of stone tool technology?

The Pattern of Early Hominin Evolution-

The understanding of early hominin evolution continues to be elusive, but what is clear is early the early phase of hominin evolution was not a straight path to Homo sapiens (p.320). Rather, it was a result of a series of adaptive radiations in which early hominins expanded geographically, adapted to and exploited different habitats and niches, and underwent varying specializations including evolutionary reversals. The origin of the hominin clade is currently established somewhere between 7 and 5 mya and may have been the result of an earlier adaptive radiation of the African apes. A second radiation was likely responsible for the diversification and geographic expansion of gracile australopithecines in Africa. A third dispersal may have resulted in the emergence of the robust australopithecines. The fourth potential radiation may have been linked to early species of Homo. The resulting picture of early hominin evolution is that of a bush (p.323); it represents a continuity of events where several dispersals led to multiple species coexisting throughout Africa during different periods. This would be a fine example of punctuated equilibrium.

Homo represents an example of a reversal in the evolutionary trend of megadonty although the causes for this reversal remain contested (p.326). Other evolutionary trends that help create the clade include larger cranial capacity and reduced dentition. More recent analyses (p.326) indicate when other factors are included with a more focused cladistic method, the adaptive shifts that signify the Homo genus actually occurred later with Homo ergaster. Homo habilis and Homo rudolfensis would actually be more cladistically similar to Australopithecus. This would create a definitive gap that may signify a major adaptive change that led to the evolutionary success to later species of Homo. If the turnover-pulse hypothesis is correct, major climate shifts would have lead to origination/extinction events, and major climate changes would have resulted in detrimental/opportunistic changes in ecological relationships. In the paleontological/archaeological record, adaptive radiations in early hominins reflect adaptive strategies from an ecological perspective. During particular periods associated with events of adaptation, early hominins adjusted to and exploited ecological niches through adaptation and specialization in terms of geographic distribution, behavior, and diet.

What underlying factors could be responsible for the multiple adaptive radiations and specializations that occurred in African apes and early hominins? The authors provide a few potential factors for each radiation. Can you think of any other potential factors and/or related specializations? The turnover-pulse hypothesis argues that extinction occurs after origination. Is there any evidence in early hominin evolution that supports/debunks this argument?

Chapter 13: Africa and Beyond: The Evolution of Homo

Evolutionary Patterns-

The species Homo erectus has undergone several name changes since its discovery in 1887 by Eugene Dubois on the island of Java (p.332). Initially regarded as the “missing link” in human evolution, Dubois named the fossil specimens considered to be from the same individual Anthropithecus erectus. He changed the name to Pithecanthropus erectus after believing the “missing link” had been discovered based on cranium measurements (p.333). The classification as the link between apes and humans was based off a single top of a hominin cranium and a complete femur although the femur is now thought to be that of a later species Homo sapiens (p.334). Peking man was discovered in 1927 by Davidson Black and was subsequently named Sinanthropus erectus (p.334). In 1951, both species were combined in to a single genus and species Homo erectus because of their greater similarities to Homo sapiens (p.335).

The oldest known and most complete fossil specimens have been recovered in the Lake Turkana region of northern Kenya and are around 1.8 million years old (p.336). Of significance is the brain size which is larger than Homo habilis by approximately 210cc at 850cc.

One of the most important discoveries for Homo erectus was the complete skeleton of a H. erectus boy on the west side of Lake Turkana. The importance is two-fold: many of the postcranial elements of Homo erectus had not been discovered, and it allows for overall body proportions and their relationships to be scrutinized (p.337). The anatomical relationships allowed paleoanthropologists to make inferences about ecological and behavioral factors attributed to the species such as life-history, subsistence, and language capacity (p.337).

Changing Views: Dates and Evolutionary Pattern-

Two views of Homo erectus have appeared as a result of the quantity of fossil specimens that have been collected (p.339). The first conclusion is that anatomical variations initially observed in Asia seem to quickly spread everywhere. The second conclusion declares that Homo erectus originated in Africa around 2 million years ago and dispersed outside Africa around 1 million years ago. The possibility that H. erectus took around 1 million years to disperse provides an important puzzle in the history of H. erectus (p.339). One of the reasons for delay may be considered on technological terms. It is suggested (p.339) that Homo erectus lacked sufficient technological development needed to expand their geographic range outside of Africa until the development of the Acheulean industry around 1.4 mya.

What are the implications of the gap in time between Homo erectus’s appearance and eventual expansion out of Africa? Current evidence (p.339) suggests that either there was no delay between evolution and dispersal of Homo out of Africa, or Asia was the origin of H. erectus at 2 mya. Recent analysis of the Modjokerto skull from Java determines the age to be between 1.8 and 1.6 million years old and is highly suggestive of an Asia origin although the actual provenance of the skull is in question (p.340). Another find in China in 1988 may also offer a precursor to H. erectus dated close to 2 mya (p.340). Both of these finds reinforces the hypothesis for an “out of Asia” origin tale of H. erectus although most still consider that H. erectus is descended directly from Homo habilis/rudolfensis approximately 2 mya in Africa (p.341).

Changing Views: Anatomy and Evolutionary Pattern-

Many anthropologists support that Homo erectus may represent multiple species based on variation viewed between separate geographically distributed populations (p.342). Homo ergaster is the new species in which the earliest African specimens have been assigned. The relationship between ergaster and erectus is considered to that of an ancestor and a descendant (p.342). This analysis continues to support the hypothesis for the origin of Homo from Africa and it attributes the appearance of H. erectus in the archaeological record in Africa as a second later dispersal from Asia back to Africa (p.342).

Some of the key anatomical elements observed in H. ergaster/erectus that differ include several differences but two appear to be significant. The first trait is the increase in brain size over time from ergaster to erectus between 850 and 1100cc. It appears to be a significant increase, but the body size increased from ergaster to erectus as well indicating that the relative brain size may have only increased minutely (p.342).

The second trait has implications for the understanding of behavior such as subsistence strategy (p.343). Homo erectus marks the initial appearance of a human nose with the nostrils facing downward which permits moisture to condensate from exhalation which would have been important in active subsistence on in a warm, arid environment (p.343).

Several other behavioral inferences can be made through the larger body size, decreased sexual dimorphism, a more robust and heavily muscled structure (compared to modern humans), and the absence of an expanded neural canal in the lower thoracic vertebrae indicate the following: Homo ergaster/erectus was subjected to routine heavy exertion, possessed an broader-ranged subsistence pattern, had less male competition, and did not possess spoken language (p.343-344). All of these traits may assist in the understanding of the behavioral ecology of H. ergaster/erectus. What sort of ecological model would be sufficient in accommodating the aforementioned trait? The authors (p.343) mention the possibility that H. ergaster/erectus may have participated in male-male cooperation. What significance would this have on the origins of modern human behavior and social structure?

Changing Patterns of Behavior-

A number of changes occurred within the genus Homo during the period that ergaster/erectus lived. The following is a list of behavioral adaptations attributed to the initial appearance and subsequent existence of ergaster/erectus (p.344):

• The first appearance of hominins outside of Africa, although other evidence may argue for Asian origins (p.340-341).
• The first appearance of systematic hunting (broader subsistence patterns and decreased male-to-male competition are possible evidence).
• The first appearance of early “Home bases”( May mark an increased sedentism, intensified resource tethering, increased social behaviors e.g. cooperation).
• Toolmaking becomes systematic (indicates increased cognitive ability and manipulation (p.345)).
• The initial use of fire.
• The first indication of an extended childhood (smaller birth canals, earlier births resulting relatively unformed brains, and the demand for social learning are factors).

In addition, life histories change from being an apelike pattern to more towards modern Homo sapiens although H. ergaster is considered intermediate of the two (p.345).

An increase in the frequency of faunal and lithic evidence in the archaeological record from early Homo through H. erectus occupations indicates hunting activity (p.345). One of the significant developments attributed to the appearance of H. ergaster/erectus is the intensification and innovation of stone tool production evident in the Acheulean Industry (mode 2 technology). The teardrop or ovate shaped handaxe is the flagship for the Acheulean tool industry (p.346). Larger tools also appear that appear to be more specific in function. What is important in the Acheulean kit is the systematic flake reduction and core preparation process as it reflects a higher level of both cognitive and manipulative ability in the conception, process, and finished product (p.346). The Acheulean technological period represents a long period of continuity with a wide geographical distribution lasting from approximately 1.4 mya to 200,000 years ago (p.346; 348).

The Movius line is a boundary between the distribution of bifaces and non-bifaces lithic tool industries (p.349 see figure 13.15). It geographically separates Africa, western Asia, and Europe from eastern and southern Asia. Bifacial reduction is nearly exclusive to the west half (observe the hybrid zone in fig. 13.15). Bifacial reduction of a stone tool means that lithic material has been removed from both dorsal and ventral sides of a core or large flake from a core. Usually this is done in some observable and systematic fashion ending in a thin, finely flaked tool. What potential causal factors can be responsible for this line?

Subsistence Practices and Settlement Patterns: Behavioral Ecology

Several hypotheses have been developed regarding early hominin subsistence development and strategies including the home-base hypothesis, the food sharing hypothesis, the scavenging hypothesis, and the advanced scavenging hypothesis (p.351-359). There is a debate that focuses on “hunting versus scavenging,” or “Man the Hunter” versus “Woman the Gatherer.” It appears that advanced scavenging may have been more feasible from both a technological and an ecological standpoint for hominins although they would have differed from the concept of modern hunter-gatherers (p.359).

Cutmarks and percussion fractures on fossil bones observed in the archaeological record and sites indicate early hunting or scavenging practices associated to the earliest signs of meat processing and consumption as early as 2.5 mya (p.359). The increased consumption of meat is considered an important factor in human evolution (p.360). Did dietary changes lead increased social behaviors such as material transport, resource intensification, and new subsistence strategies? Does the increase in modified faunal remains associated with lithic material suggests cooperation in resource procurement visible in the archaeological record as “kill sites,” or does it represents Homo as a scavenger?

NEW SIVALADAPID PRIMATES FROM THE EOCENE PONDAUNG FORMATION OF MYANMAR AND THE ANTHROPOID STATUS OF AMPHIPITHECIDAE

Fossil primates from the late middle Eocene Pondaung Formation of Myanmar have been used to construct the evolutionary history of anthropoids. However, the most abundant anthropoid fossil currently used from the Pondaung Formation have proven to be controversial in reconstructing the evolutionary tract. This article describes the findings of two new primate fossils, Paukkaungia parva and Kyitchaungia takaii for the middle Econene Pondaung Formation of Myanmar. The fossil remains of the lower dentition from both Paukkaungia and Kyitchaungia are closely related to other sivaladapid primates. Therefore, these new findings, for the first time, are able to document the presence of adapiforms in the Pondaung Formation, and enhance the taxonomic and paleoecological diversity of the late middle Eocene primates of Myanmar.



Beard, K. C., Marivaux, L., Soe Thura Tun, Aung Naing Soe, Chaimanee, Y., Wanna Htoon, Marandat, B., Htun Htun Aung, and Jaeger, J.J. 2007. New sivaladapid primates from the Eocene Pondaung Formation of Myanmar and the anthropoid status of Amphipithecidae. Bulletin of Carnegie Museum of Natural History 39: 67-76.

Proximal Femoral Anatomy of a Sivaladapid Primate From the Late Middle Eocene Ponduang Formation (Central Myanmar)

Proximal Femoral Anatomy of a Sivaladapid Primate From the Late Middle Eocene Ponduang Formation (Central Myanmar)
2008

By: Laurent Marvaux, K Christopher Beard, Yaowalak Chiamanee, Jeans-Jacques Jaeger, Bernard Marandat, Aung Naing Soe, Soe Thura Tun, and Aung Aung Kyaw

Printed in American Journal Of Physical Anthropology 137:263-273.

This article examines the morphology of a proximal femur recovered from the Ponduang formation in central Myanmar. The proximal femur is part of the hip joint “which supports the weight of the body in both static and dynamic postures” (pp 269). The specimen that was utilized for analysis was well preserved and represented a significant portion of the femur. From the measurements that were obtained the research team was able to discern features such as, the creature was a proficient leaper which is evident because the “overhang of the trochanter” would have provided more leverage (pp270). Another characteristic of the femur suggested that the creature was able to freely move its hip a possible sign of climbing. In general these features suggested that this primate was “engaged in a kind of active arboreal quadrupedalism with some degree of proficiency” (pp 270).
What is interesting about this specimen is that in the Pongduang formation only two primate clades had been previously identified; the eosiimids and the amphipithecids. However, this new specimen exhibits characteristics of adapiforms and extent strepsirhines. This, in turn, challenges what was previously thought of this area and suggests that there was a greater diversity of primates in the area than previously thought (pp 263-265).

Earliest Complete Dentition of an Anthropoid from the Eocene

A new species located in the Yuanqu Basin, Shanxi Province, China named eosimias centennicus has shed light on the formation of early primates. The specimens collected of this small primate include a complete lower mandible (only lower left incisors missing) never before found. The information stemming from this dentition confirms anthropoid affinities of Eosimiidae, which in turn gives new data of an earlier structural step in the origin and evolution of higher primates despite its primitive characteristics. Given this new information geographic assessments can be made; it can be argued that by the mid-Eocene there were present higher primates living from Algeria to eastern China.

Beard, K Christopher, Tong, Yongsheng, Dawson, Mary R, Wang, Jingwen, Huang, Xueshi.
"Earliest Complete Dentition of an Anthropoid Primate from the Late Middle Eocene of Shanxi Province, China" Science. Washington: Apr 5, 1996, 272(5258) pg. 82-85

Evidence for Anthropoid Origins

Chris Beard is a chief proponent of the "Out of Asia" hypothesis for anthropoid (monkeys, apes and humans) origins. His latest find, Ganlea megacanina, offers further support for this idea and Beard presents this evidence in an article published in the Proceedings of the Royal Society B this past July. The article discusses the specifics of the dental morphology of Ganlea at length and compares its features with those found in extant primates inhabiting the New World. The similiarities between the fossil and these NWM centers around atypical apical wear patterns on the lower canines that are consistent with diets which include hard, tough fruits that contain seeds. The new fossil species also exhibit a high level of canine robusticity not found among the other amphipithecids, members of the Amphipithecidae family, but do show apical wear patterns similar to those of Ganlea. This variation in canine robusticity is also found among extant pitheciins. The adult body mass of Ganlea was estimated at about 2 kg utilizing Glenn Conroy's mass estimation based on the area of the first molar of primates. This weight is comparable to that of the white-faced saki monkey (Pithecia pithecia) pictured below. The link to Beard's article is also below.



Article: http://rspb.royalsocietypublishing.org/content/276/1671/3285

Chapter 9: Searching for the First Hominins

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.

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 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.

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?