Saturday, March 27, 2010

Transitional Species, Ancestral Species, and Missing Links

Although it has been established that creationists believe in microevolution ("Minor changes in size and shape [that] occur over time" (33) ), creationists do not believe in macroevolution ("[When] one very different kind of animal or plant [comes] from another" (33) ). In proving macroevolution is true, scientists have looked to the fossil records. Compare, contrast, and provide examples of transitional species, ancestral species and missing links. How do those three terms relate to macroevolution? Which of the three terms is the hardest to find in the fossil record and why? Does a missing link have to look like an intermediate between the two species, why or why not?

1 comment:

  1. To try and prove that evolution is true, evolutionists try to point to the ancestral species shared by different species of organisms.An ancestral species is a species from which a different species has emerged. Ancestral species usually have very similar traits to the species that had diverged from it. For example, the genus "homo" (humans) diverged from the genus Australopithecines about 2.4 million years ago; this is a close ancestral species because it was a hominid as well ("Evolution of early humans", Cambridge Encyclopedia of Human Evolution). Similarly, a transitional specices, often called a "missing link", represents the species from which two or more separate species of organisms diverged at a certain point in history. These are possibly the most important pieces of evidence proving the truth of the theory of evolution. This can explain why people were hesitant to believe Darwin's theory of evolution right away, due to the lack of missing links to support his claims. However, soon after "On the Origin of Species" was published, Archaeopteryx was found. This was the earliest form of bird found, and appeared to provide a transitional species between dinosaurs and birds, as it obviously had traits of both kinds of animal ( Transitional species differ from ancestral species because transitional species link two species that are not directly connected in the same evolutionary chain but rather exist on different branches, having diverged from each other earlier in history. Ancestral species are species from which an organism has directly evolved ( Ancestral and transitional species relate to macroevolution because they help create a more complete evolutionary tree explaining how each species came to be and what traits eventually caused these species to diverge. Of course there will never be a complete evolutionary tree, because there have been way too many species that existed and there aren't a lot of fossils to make a complete picture on the orgiin of every species. Gathering the evidence we do have from transitional and ancestral fossils, however, can help provide evidence that macroevolution is without a doubt true. Missing links are difficult to find because there is no single missing link to prove the truth of evolution. Since we currently have such a tiny percentage of the amount of species that have existed in the history of the world, it's tough to determine what is a transitional form. Also, since all people have are fossils, we may not know that we have transitional species because its body shape is so similar to a similar ancestral species. Last, it's difficult to find missing links simply because of how tough it is to find fossils (22). Only certain specific conditions allow fossils to be preserved, so there are few places that actually contain fossils; as a result, the likely-hood of finding a new species of fossil in an old area is very low ( A missing link doesn't necessarily have to look like a complete cross between two species that have diverged from it, but it should be "a species showing a mixture of traits from organisms that lived both before and after it" (35). Thus, a missing link should resemble other species slightly. For example, on page 36, Coyne gives the example of Tiktaalik roseae, which has a bone structure composed of both fin structures and walking limb structures, suggesting it is a missing link between Eusthenopteron foordi (early lobe-finned fish) and Acanthostega gunnari (land-dwelling tetrapod).