The fossil record is rich in its biological and ecological information (Behrensmeyer, 103), but very few fossil are persevered. Leaving the fossil record uneven and incomplete. The natural processes affect our fossil record by giving us a set sampling size even before our research begins. Taphonomy seeks to understand the natural processes in order for information to be collected and evaluated correctly.
Taphonomy can be defined as the study of post-mortem, pre-burial remains of an organism from the biosphere into the lithosphere, or more generally characterized by Behrensmeyer and Kidwell as “the study of processes of preservation and how they affect information in the fossil record.” “Today, taphonomy focuses more on a geobiological understanding of the earth, grounded on the postmortem process that recycle biological materials and affect our ability positively or negatively to reconstruct past environments and biotas” (Behrensmeyer,104). However there are several factors and processes that affect the preservation of skeletal remains. These are: the amount and durability of the remains. Secondly, the physical, chemical, and biological components at pre-burial site that includes, air, water, and soil. Third, the amount of time the remains are exposed on the surface and how quickly the remains are buried. Next, the digenetic conditions within the upper part of the sedimentary column, this includes microbial process, physical reworking, or unequal amounts of biochemical in the soil. Lastly, the depth and location of the remains in the sedimentary. Most of our longest surviving fossils are commonly found in stable cratonic margins or interiors and continental rifts margins; for they escape the tectonic recycling. Some destructive factors during these stages are commonly referred to as: bioerosion, scavenging, dissolution, abrasion, rounding, disarticulation, and weathering which all affect the outcome of the remains. With all these factors and several more it might seem that the chance to reconstruct the past is impossible, but through the combination of understanding natural process, a more complete research of materials in prehistoric history, and ingenious experiments and observation, it is becoming possible to solve specific problems in our fossil record (Lewin, 95).
There are several ways we can use taphonomy to aid our understanding and to resolve certain questions. Take for example, a taphonomists can examine the characteristics of contemporary kill site, where animals have been killed, processed, and eaten by various predators, including humans. This enables the taphonomist to monitor how each type of predator consumes their prey, while noting which bones are carried off or cracked open for marrow, and how bones are scattered throughout the site. This data enables archaeologists to develop a profile of characteristics of a historical kill site (Boyd,318).
Another example how taphonomy can be used, is by looking at modern sites where skeletal remains are affected by sediments rapidly moving through water. These sediments will leave a number of distinctive characteristics on the bones, which can be compared that to of a historical sites with the same sediment mixture. If the markings do not match then taphonomists can find out whether the distinctive marks were made from animals gnawing on the bones, or even caused by flaked-stone tools. Taphomomic data is also been applied to other fields such as paleobiology, paleoceanography, ichnology and biostratigraphy
Behrensmeyer, Anna, with Susan Kidwell, and Robert Gastaldo
2000 “Taphonomy and Paleobiology.” Paleobiology Society 26(4):103-147
Body, Robert and Joan B. Silk
2003 How Humans Evolved. New York: W.W. Norton and Company Inc.
Lewin, Roger, and Robert A. Foley
2004 Principles of Human Evolution. Malden, MA: Blackwell Publishing
Shipman, P.
1981 Life history of a fossil: An introduction to taphonomy and paleoecology. Harvard
University Press
Monday, October 5, 2009
Gradualism and Punctuated Equilibrium
Gradualism and Punctuated Equilibrium
I started researching this topic by skimming through my old (2003) textbook from my Human Evolution class that I took as an undergraduate. The authors make no mention of these two terms within the text. They do acknowledge that although slow rates of change are the typical units observed within the fossil record, rapid evolutionary events most likely happened, and the lack of evidence is a result of an incomplete fossil record ( Boyd and Silk 2003:22). The textbook for our seminar is a 2004 edition and dedicates several pages to gradualism and punctuated equilibrium. To me, this represents the variation in academia when it comes to challenging or accepting new concepts.
Gradualism may be defined as the process in evolution that accumulates small units of change at a steady rate, over long temporal periods. The gradual accumulation of new adaptations causes a genetic divergence of offspring from the parent, or ancestral species (Lewin and Foley 2004:52). Gradualism is therefore characterized as being a slow process that remains consistent and constant where change is cumulative within a species. Gradualism is essentially a fundamental part of the theory of Modern Synthesis (1942) that is a union of ideas which resulted from the differences that remained between strict Darwinism and evolutionary theory. Modern Synthesis has three principal components of which the first is gradualism. Although gradualism was originated by James Hutton in 1795, it traveled into Charles Lyell’s repertoire in the form of Unitarianism. It then influenced Charles Darwin and his theory of evolution. It is important to point out that
Punctuated Equilibrium essentially describes that species go through static periods with relatively little change that are accentuated by rapidly occurring modifications resulting in speciation. The species then return to a static period. Lewin and Foley (2004:52) indicate that separation of a daughter species from the ancestral species may still occur under punctuated equilibrium, but mainly it occurs through drifts in smaller, isolated populations. Steven Jay Gould and Niles Eldredge published their theory in 1972. Their work was influenced by Ernest Mayr, who also was a key contributor to Modern Synthesis, and Michael Lerner. One of the important differences between punctuated equilibrium and gradualism is how speciation is viewed. Punctuated equilibrium views adaptation as a possible result of speciation, while gradualism views it as a cause of speciation. In addition Gould and Eldredge view is similar to saltation only in the idea that change occurs rapidly. For Gould and Eldredge, adaptation occurs as result of speciation, but follows Darwinian fundamentals in doing so.
Gradualism and punctuated equilibrium may represent two different gears of the same mechanism; gradualism is the hour hand and punctuated equilibrium is the minute hand in which both are enclosed in a mechanism designed (or evolved) to measure time.
Gould and Eldredge (1993) celebrated the acceptance of their concept of punctuated equilibrium into the realm of theory. Can both theories actually coincide if some of the principal components to each contradict each other?
References
Boyd, Robert and Joan B. Silk
2003 How Humans Evolved. 3rd Edition.
Gould, Stephen J. and
1993 Punctuated Equilibrium Comes of Age. Nature. 18 November 1993 (366) :
223-227.
Lewin, Roger and Robert A. Foley
2004 Principles of Human Evolution. 2nd Edition.
Publishing.
Links:
http://www.talkorigins.org/faqs/punc-eq.html
http://evolution.berkeley.edu/evosite/evo101/VIIA1bPunctuated.shtml
http://www.blackwellpublishing.com/ridley/a-z/Phyletic_gradualism.asp
http://www.creationdefense.org/76.htm
http://www.istheory.yorku.ca/punctuatedequilibriumtheory.htm
Catastrophism and Uniformitarianism
The geological concepts of Catastrophism and Uniformitarianism relate to a scientific debate on how the earth has been affected in the past to create the modern conditions of land formation (and degradation) and speciation. Both concepts stem from Charles Lyell's (1797-1875) and William Whewell's (1794-1866) scholarly debate on geological change that still are applicable today (Baker, 1998).
Catastrophism is the belief that the earth has been changed historically by dramatic sudden natural catastrophes such as meteors, floods, or volcanic eruptions, causing mass extinctions and the change of land formations in its wake (Bak and Paczuski, 1996). Uniformitarianism, on the other hand, applies to the belief that the Earth is affected by slow, gradual change with change in land forms and extinction as naturally occurring processes (Bak and Paczuski, 1996). Lyell argued in Principles of Geology (1833) that uniformitarianism of natural processes has created the present conditions in nature - much aligned with Darwin's views of speciation (Bak and Paczuski, 1996). It was Whewell's critique of Lyell's work in 1837 that the terms 'Catastrophism' and 'Uniformitarianism' were defined, with Whewell's logic putting forth that the Earth's geological history is punctuated by certain catastrophic events that caused change to the natural order (Baker, 1998).
Modern thought combines both sides of the argument, using the fossil record and geological dating to determine Earth's history of extinction and change through processes relating to catastrophism and uniformitarianism.
References:
Related Links: http://www.pibburns.com/catastro/extinct.htm http://www.catastrophism.com/ ....and the creationist argument: http://www.answersincreation.org/catastrophism.htm |
Absolute Dating Techniques
Steve Jones briefly, when discussing the geological record, writes about why “the answer to time lies not with deposition, but with decay (195).” This is evident by studying chemical breakdowns which can be used to determine how old matter is on earth. One such technique is known as Carbon-14 Dating.
In 1949, Williard F. Libby, a physical chemist discovered radiocarbon dating. He was able to explain that in the atmosphere, nitrogen particles change into a new form of carbon when atomic nuclei are hit by cosmic rays, carbon-14 rather than the usual carbon-12 due to the amount of 14 particles. Because it is naturally unstable, it begins to break down at once, and continues to decay for thousands of years. Every living organism is made up of this carbon which is constantly replaced while the creature is alive. However, upon death, no new carbon is added and begins to decay at a constant rate. Scientists were able to determine that there exists a half-life in the rate of carbon-14 decay. Every 5,730 (plus or minus a few) years the carbon material is cut in half. By knowing this, researchers are able to calculate how old an organic material is based on how much carbon is left.
The value of radiocarbon dating is in the vast amount of objects it can date, anything from buildings made of wood, seashell jewelry, leather clothes, hearth deposits, and coprolite remains. Unfortunately, contamination is an easy and common threat by the way of modern particles easily transferred onto older ones. Scientists also need large amounts of the remains in order to get a sizable amount of carbon for testing, as carbon-14 only accounts for 0.0000000001% of the carbon isotopes in the body, which may be difficult to come by.
Another method for dating is the analysis of other isotope compositions. Argon/Potassium (Ar/K) dating, for example, is similar to radiocarbon dating described above with argon as the parent material. A sample is instead studied to find how much potassium is present. Because its half-life is much longer, this technique can be used to date sites millions of years old and early hominid remains.
Of importance to the topic of this course is that “time can be measured only by change (194).” The alteration from nitrogen to carbon, and potassium to argon, gives us a constant time frame for how old the earth really is. By analyzing these changes can we discern how much time has elapsed allowing for the feasibility of natural selection.
Additional sources:
Balme, Jane and Paterson, Alistair, ed., Archaeology in Practice: A Student Guide to Archaeological Analyses, Blackwell Publishing, 2006
Thomas, David Hurst; Archaeology: Down to Earth, 2nd ed.; Harcourt Brace College Publishers, 1999
In 1949, Williard F. Libby, a physical chemist discovered radiocarbon dating. He was able to explain that in the atmosphere, nitrogen particles change into a new form of carbon when atomic nuclei are hit by cosmic rays, carbon-14 rather than the usual carbon-12 due to the amount of 14 particles. Because it is naturally unstable, it begins to break down at once, and continues to decay for thousands of years. Every living organism is made up of this carbon which is constantly replaced while the creature is alive. However, upon death, no new carbon is added and begins to decay at a constant rate. Scientists were able to determine that there exists a half-life in the rate of carbon-14 decay. Every 5,730 (plus or minus a few) years the carbon material is cut in half. By knowing this, researchers are able to calculate how old an organic material is based on how much carbon is left.
The value of radiocarbon dating is in the vast amount of objects it can date, anything from buildings made of wood, seashell jewelry, leather clothes, hearth deposits, and coprolite remains. Unfortunately, contamination is an easy and common threat by the way of modern particles easily transferred onto older ones. Scientists also need large amounts of the remains in order to get a sizable amount of carbon for testing, as carbon-14 only accounts for 0.0000000001% of the carbon isotopes in the body, which may be difficult to come by.
Another method for dating is the analysis of other isotope compositions. Argon/Potassium (Ar/K) dating, for example, is similar to radiocarbon dating described above with argon as the parent material. A sample is instead studied to find how much potassium is present. Because its half-life is much longer, this technique can be used to date sites millions of years old and early hominid remains.
Of importance to the topic of this course is that “time can be measured only by change (194).” The alteration from nitrogen to carbon, and potassium to argon, gives us a constant time frame for how old the earth really is. By analyzing these changes can we discern how much time has elapsed allowing for the feasibility of natural selection.
Additional sources:
Balme, Jane and Paterson, Alistair, ed., Archaeology in Practice: A Student Guide to Archaeological Analyses, Blackwell Publishing, 2006
Thomas, David Hurst; Archaeology: Down to Earth, 2nd ed.; Harcourt Brace College Publishers, 1999
The Cambrian Explosion
The Cambrian Explosion is a fitting term to describe the actual event, which was an enormous boom in the fossil record of complex organisms, even if it was originally dubbed this for the wrong reason. It was originally thought that this was a massive speciation event because there was no fossil record dating back before the Cambrian at Darwin’s time (Ridley 2004). We know now that the Cambrian Explosion marks the first appearance of animals that possessed hard body parts capable of preservation (Jones 2000). Prior to this adaptation animal remains were soft and fragile, thus decaying soon after the organism’s death. There are several hypotheses that attempt to explain this major step in evolution. Life biologists offer the emergence of predators, visually hunting predators especially, to explain the sudden appearance of hard parts as a means of defense (Ridley 2004). This is supported by direct evidence of predators’ gut contents, bite markings and jaw characteristics (M. 2009). Physical scientists look to an increase in oxygen levels or the glaciation of the Earth at that time to explain an increase in body size (S. 2009). It would seem that the combination of all the above could offer a more complete explanation and a lot of current research in biology, paleontology and molecular studies is focused on this period (Ridley 2004). No matter what caused the emergence of fossils, it is important to remember that the Cambrian Explosion was exactly that – an emergence of fossils, not specific animals.
The image is a drawing of Hallacigenia sparsa, which was an inhabitant of the Burgess Shale in British Columbia, Canada. The fossils were originally interpreted to have the animal walk on its spikes and later it was realized it was drawn upside down. This type of artistic interpretation, or misinterpretation, of the fossil record contributed to the pre-1940 belief of radical speciation in the Cambrian Explosion. With such bizarre looking animals people continued to ask how these characters could have evolved and could selection have been a plausible mechanism for their appearance (Jones 2000).
Literature Cited
Jones S. 2000. Darwin’s ghost: the origin of the species updated. London: Ballatine Publishing.
M. SC. 2009. Burgess shale. In: Ruse M, Travis J, editors. 2009. Evolution: The first four billion years. Cambridge: The Belknap Press of Harvard University Press.
Ridley M. 2004. Evolution, third edition. Malden: Blackwell Publishing.
S. JW. 2009. Organismic evolution and radiation before the Cambrian. In: Ruse M, Travis J, editors. 2009. Evolution: The first four billion years. Cambridge: The Belknap Press of Harvard University Press.
Mutual Affinities; Morphology; Embryology; Rudimentary Organs
Humans have an inherent drive to classify the environment around them, perhaps due to the need to simplify into groups the many objects they come into contact with and to keep their world organized. Over time there is evidence of this in the array of classification systems man has arbitrarily created, as Jones points out (276), but in this chapter the author explains why there is only one true “arrangement” for life on earth, a classification based on a hierarchy of shared descent.
The classifying system Jones writes about was first created by Carl Linnaeus (1707-1778), a Swedish zoologist and botanist. His adoption of a binomial nomenclature (the scientific naming of a species) was the genesis of the taxonomic filing cabinet we use to sort living creatures today. The Linnaean system is a hierarchical ordering based on observable physical characteristics in plants and animals. Animals that share traits are within the same unit. From an overarching Kingdom down to a more specific Species, every bird, wolf, pine tree, and fish can be identified and placed into categories. Though his initial plan has been altered over time, Linnaeus is still credited with the concept.
Today the Linnaean taxonomic system is extremely important for understanding evolution. “It depends on a single idea: that groups sharing traits not present in others must descend from a common ancestor (280).” We are able to see by looking at shared characteristics just how far back the ancestral line may go and who is related when. We are able to determine relatedness, what evolved from what, by which traits we have in common. Humans are related to fish, because they both have backbones, but we are closer to other mammals because we possess hair and produce live births. These traits are evidence of evolution in the past. Some traits are stronger determinants of this. How do we decide what traits count and which ones don’t? In other words, why aren’t we a closer cousin to the iguana (we have five fingers, right?) than to the horse (with no fingers)?
Common descent can be more easily ascertained today. Where there used to be disagreement on where to place specific plants and animals, it can now be determined by analyzing the genetic landscape of a given species. Studying DNA patterns reveal we, as humans, have much in common with bats and rabbits; dogs share many of the same genes with whales and elephants. Known as cladistics, this approach focuses on classifying groups, or clades, according to shared characteristics and discovering just how far back our common ancestors go. For instance, all vertebrates are in one clade, and tetrapods (vertebrates with four limbs) form another clade within the vertebrate clade. These groupings can be derived from common characteristics, behaviors, or anatomical resemblances. The important point here is that all living creatures are related and have a shared ancestry which can be traced. From this chapter and what we have previously read, how is the study of cladistics more reliable than the fossil record in determining who our common ancestors are? Also, what is the difference between cladistics and traditional Linnaean taxonomy?
For further reading:
-Cladistics: The Theory and Practice of Parsimony Analysis; Ian Kitching, Peter L. Forey, David Williams, Christopher Humphries
-Cladistics: A Practical Course in Systematics; Peter L. Forey, Christopher Humphries, Ian Kitching
-Transformed Cladistics, Taxonomy and Evolution; N. R. Scott-Ram
-Cladistics and Archaeology; Michael J. O'Brien, Daniel S. Glover, John Darwent, R. Lee Lyman
Morphology refers to the study of an organism’s structure and anatomy. In many cases looking at internal bones and organs, and external body parts, can shed light on how closely related different species are. Why, for example, do most mammals have similar extensions such as arms and flippers? Jones argues that duplication is key. Repetition in molecule formation allows the body to form and mutate while keeping “the stamp of its shared ancestry (293).” Genes determine what is to be copied, when and where. Having a multitude of teeth is an example of duplication through natural selection. One mutation, one wrong order in the wrong place, can cause a fly to have multiple wings, or a flower to have several petals. Though a body may create separate modules and copy itself, there also evolves individual characteristics in these groupings. How, then, does one module end up a brain and the other a tail?
Embryology is basically the study of life in the stages before birth, hatching, or germination. Something as complex as the human brain, or the structure of a deer or oak tree, always begins life as an embryo. Analyzing the make-up of a fetus or an egg may give us answers about our ancestors, as “each animal relives its ancient history” in these early stages of life (298). The likenesses between animals, known as homology, which we now know to be evidence of a shared ancestor and not similar environments, can be clearly seen at the embryonic stage. Before an organism matures it showcases the same early cell and gene structures as other organisms at the same stage. It is only when it grows to adulthood that the specific changes which makes it unique emerges. Thus the genes of a mouse in the first week can be almost exact to that of a fruit fly. Evolutionary developmental biology can reveal how similar we are to other species thus demarcating the family tree we all belong to, showing “how universal is the history revealed before birth (301).” The embryo gives us an image of what conditions were like for our earlier, less altered, ancestors. How else does embryology help fit in and bolster Darwin’s three principles of natural selection, heredity, and variation?
Indiana University’s human embryo animations:
http://www.indiana.edu/~anat550/embryo_main/index.html
Rudimentary Organs are structural parts and organs which have lost their original function and are no longer useful to the organism. We see lots of evidence of these leftover parts in the embryonic stage and usually they disappear, but there are some that develop into adulthood. Why, for instance, do humans have appendixes, and why do male mammals have nipples if they do not lactate for their children? Jones maintains that these leftover organs once had utility for our ancestors in the past. Some organs and bones, such as those in the ear canal, may have had duel purposes, and evolution has selected for the elimination of one purpose over the other. “Natural selection does not hesitate to pick up and use whatever becomes available (304).” It also won’t hesitate to lose organs that are too burdensome or costly. It would seem troublesome to find so many errors in repetition in a system that seems geared toward removing them for the sake of efficiency. But it is within these leftover parts that we see greater relatedness among species as it retains traces of the past. What typically happens to vestigial structures over time, and why else are these organs “evidence of descent with modification?” Also, why might it be dangerous to assume that all “vestiges” have no function at all?
Additional links concerning rudimentary organs:
http://www.talkorigins.org/faqs/comdesc/section2.html#vestiges
http://www.livescience.com/animals/top10_vestigial_organs.html http://news.nationalgeographic.com/news/2009/07/090730-spleen-vestigial-organs.html
The classifying system Jones writes about was first created by Carl Linnaeus (1707-1778), a Swedish zoologist and botanist. His adoption of a binomial nomenclature (the scientific naming of a species) was the genesis of the taxonomic filing cabinet we use to sort living creatures today. The Linnaean system is a hierarchical ordering based on observable physical characteristics in plants and animals. Animals that share traits are within the same unit. From an overarching Kingdom down to a more specific Species, every bird, wolf, pine tree, and fish can be identified and placed into categories. Though his initial plan has been altered over time, Linnaeus is still credited with the concept.
Today the Linnaean taxonomic system is extremely important for understanding evolution. “It depends on a single idea: that groups sharing traits not present in others must descend from a common ancestor (280).” We are able to see by looking at shared characteristics just how far back the ancestral line may go and who is related when. We are able to determine relatedness, what evolved from what, by which traits we have in common. Humans are related to fish, because they both have backbones, but we are closer to other mammals because we possess hair and produce live births. These traits are evidence of evolution in the past. Some traits are stronger determinants of this. How do we decide what traits count and which ones don’t? In other words, why aren’t we a closer cousin to the iguana (we have five fingers, right?) than to the horse (with no fingers)?
Common descent can be more easily ascertained today. Where there used to be disagreement on where to place specific plants and animals, it can now be determined by analyzing the genetic landscape of a given species. Studying DNA patterns reveal we, as humans, have much in common with bats and rabbits; dogs share many of the same genes with whales and elephants. Known as cladistics, this approach focuses on classifying groups, or clades, according to shared characteristics and discovering just how far back our common ancestors go. For instance, all vertebrates are in one clade, and tetrapods (vertebrates with four limbs) form another clade within the vertebrate clade. These groupings can be derived from common characteristics, behaviors, or anatomical resemblances. The important point here is that all living creatures are related and have a shared ancestry which can be traced. From this chapter and what we have previously read, how is the study of cladistics more reliable than the fossil record in determining who our common ancestors are? Also, what is the difference between cladistics and traditional Linnaean taxonomy?
For further reading:
-Cladistics: The Theory and Practice of Parsimony Analysis; Ian Kitching, Peter L. Forey, David Williams, Christopher Humphries
-Cladistics: A Practical Course in Systematics; Peter L. Forey, Christopher Humphries, Ian Kitching
-Transformed Cladistics, Taxonomy and Evolution; N. R. Scott-Ram
-Cladistics and Archaeology; Michael J. O'Brien, Daniel S. Glover, John Darwent, R. Lee Lyman
Morphology refers to the study of an organism’s structure and anatomy. In many cases looking at internal bones and organs, and external body parts, can shed light on how closely related different species are. Why, for example, do most mammals have similar extensions such as arms and flippers? Jones argues that duplication is key. Repetition in molecule formation allows the body to form and mutate while keeping “the stamp of its shared ancestry (293).” Genes determine what is to be copied, when and where. Having a multitude of teeth is an example of duplication through natural selection. One mutation, one wrong order in the wrong place, can cause a fly to have multiple wings, or a flower to have several petals. Though a body may create separate modules and copy itself, there also evolves individual characteristics in these groupings. How, then, does one module end up a brain and the other a tail?
Embryology is basically the study of life in the stages before birth, hatching, or germination. Something as complex as the human brain, or the structure of a deer or oak tree, always begins life as an embryo. Analyzing the make-up of a fetus or an egg may give us answers about our ancestors, as “each animal relives its ancient history” in these early stages of life (298). The likenesses between animals, known as homology, which we now know to be evidence of a shared ancestor and not similar environments, can be clearly seen at the embryonic stage. Before an organism matures it showcases the same early cell and gene structures as other organisms at the same stage. It is only when it grows to adulthood that the specific changes which makes it unique emerges. Thus the genes of a mouse in the first week can be almost exact to that of a fruit fly. Evolutionary developmental biology can reveal how similar we are to other species thus demarcating the family tree we all belong to, showing “how universal is the history revealed before birth (301).” The embryo gives us an image of what conditions were like for our earlier, less altered, ancestors. How else does embryology help fit in and bolster Darwin’s three principles of natural selection, heredity, and variation?
Indiana University’s human embryo animations:
http://www.indiana.edu/~anat550/embryo_main/index.html
Rudimentary Organs are structural parts and organs which have lost their original function and are no longer useful to the organism. We see lots of evidence of these leftover parts in the embryonic stage and usually they disappear, but there are some that develop into adulthood. Why, for instance, do humans have appendixes, and why do male mammals have nipples if they do not lactate for their children? Jones maintains that these leftover organs once had utility for our ancestors in the past. Some organs and bones, such as those in the ear canal, may have had duel purposes, and evolution has selected for the elimination of one purpose over the other. “Natural selection does not hesitate to pick up and use whatever becomes available (304).” It also won’t hesitate to lose organs that are too burdensome or costly. It would seem troublesome to find so many errors in repetition in a system that seems geared toward removing them for the sake of efficiency. But it is within these leftover parts that we see greater relatedness among species as it retains traces of the past. What typically happens to vestigial structures over time, and why else are these organs “evidence of descent with modification?” Also, why might it be dangerous to assume that all “vestiges” have no function at all?
Additional links concerning rudimentary organs:
http://www.talkorigins.org/faqs/comdesc/section2.html#vestiges
http://www.livescience.com/animals/top10_vestigial_organs.html http://news.nationalgeographic.com/news/2009/07/090730-spleen-vestigial-organs.html
Sunday, October 4, 2009
Archaeopteryx and missing links
Problems with Missing Links:
According to Jones (1999) and Olsen (1981) the major problem with missing links is the imperfection in the geological record. This imperfection produces gaps in the biological timeline of species throughout history; Jones suggests that roughly one percent of species are subjected to conditions favorable for fossilization. This coupled with the natural processes that destroy the geological record, such as water erosion and the systematic destruction of the ocean floor, suggests that many of the “missing links” may be lost to us forever.
This imperfection in the geological record and scanty evidence for missing links has produced much descent among the anti-evolution population. The anti-evolutionist camp often cites these issues as evidence that evolution is indeed a falsified theory. However, there is evidence of missing links in the fossil record, one of the best known species being that of Archaeopteryx.
Archaeopteryx a missing link:
The fossil Archaeopteryx was first discovered in 1860, and to date seven specimens and a feather comprise the complete collection of Archaeopteryx specimens. Archaeopteryx lived in the late Jurassic period, about one hundred and fifty million years, in the area that is now present day Europe, and was roughly the size of a pigeon. Archaeopteryx both reptilian characteristics and avian characteristics, thus it is thought to represent a missing link between dinosaurs and birds.
Archaeopteryx possessed well developed primary and secondary flight feathers, evident that it could at least glide, if not completely able to fly. It also possessed an enlarged deltopectoral crest, indicating the presence of muscles that aid in flight. However, some have argued that Archaeopteryx was not capable of flight, and that Archaeopteryx developed feathers for insulation rather than flight. It is still believed that while Archaeopteryx appeared birdlike on the outside, due to the presence of feathers, that it was much more closely related to reptiles, evident in its skeletal likeness to reptiles.
Archaeopteryx has a striking physiological likeness to coelurosaurid dinosaurs, small active bipedal dinosaurs with raptorial forelimbs. Archaeopteryx resembles these dinosaurs so much that a specimen that preserved without feathers was misidentified as Compsagnathus, a small coelurosaurid dinosaur.
Thus the myriad of characteristics both avian and reptilian suggests that Archaeopteryx represents a link between dinosaurs and birds.
References
Jones, Steve.
1999. Darwin’s Ghost: The Origin of Species Updated. Ballantine publishing. London
Ruben, John.
1991. Reptilian Physiology and the Flight Capacity of Archaeopteryx. Evolution. 45(1). Pp 1-17.
Olsen, Everett C.
1981. The Problem of Missing Links: Today and Yesterday. The Quarterly Review of Biology. 56(4). Pp405-442.
Feduccia, Alan.
1974. Endothermy, Dinosaurs, and Archaeopteryx. Evolution. 28(3). Pp 503-504.
http://www.enchantedlearning.com/subjects/dinosaurs/facts/Archaeopteryx/
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