From Chris Colby And now, for those of you who are still with me. I have a few comments ab

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From Chris Colby And now, for those of you who are still with me... I have a few comments about "transitional fossils" in general. When _The Origin Of Species_ was first published, the fossil record was poorly known. At that time, the complaint about the lack of transitional fossils bridging the major vertebrate taxa was perfectly reasonable. Opponents of Darwin's theory of common descent (the theory that evolution has occurred; not to be confused with the separate theory that evolution occurs specifically by natural selection) were justifiably skeptical of such ideas as birds being related to reptiles. The discovery of _Archeopteryx_ only two years after the publication of _The Origin of Species_ was seen a stunning triumph for Darwin's theory of common descent. _Archeopteryx_ has been called the single most important natural history specimen ever found, "comparable to the Rosetta Stone" (Alan Feduccia, in "The Age Of Birds"). O.C. Marsh's groundbreaking study of the evolution of horses was another dramatic example of transitional fossils, this time demonstrating a whole sequence of transitions within a single family. Within a few decades after the _Origin_, these and other fossils, along with many other sources of evidence (such as developmental biology and biogeography) had convinced the majority of educated people that evolution *had* occured, and that organisms *are* related to each other by common descent. (Whether evolution occurs by natural selection, rather than by some other mechanism, is *another question entirely* and is the topic of current evolutionary research.) Since then *many* more transitional fossils have been found. Typically, the only people who still demand to see transitional fossils are creationists who have been reading 100-year-old anti-evolution arguments, and who are either unaware of the currently known fossil record or are unwilling to believe it for some reason. When presented with a transitional fossil, such creationists often then want to see the transitions between the transitions--- or, as Pilbeam complained, "as soon as you find a missing link, you've just created two more missing links". Alternatively, creationists will often state that the two groups being bridged by the transitional fossil are really the same "kind" (a term that has *no* meaning in modern biology) and that therefore "real evolution" hasn't occurred. This often leads to a weasely backtracking in which *no* transitional fossil, however dramatic, no matter what disparate groups it connects, will ever be accepted by a creationist. Biologists justifiably find this attitude irritating, and any creationist taking this tack can expect to have testy biologists demanding that he/she clearly define "kind" before the discussion goes any further. Creationists also sometimes say "All right, so you have a transitional fossil from X to Y -- but you don't from Y to Z!" It is unreasonable to expect the fossil record to be absolutely complete. It is highly unlikely for *any* organism to get fossilized, and to demand a perfect sequence of fossils of all species from all times and all locations, perfectly preserved in rocks that are not plowed under or eroded away, and not taken by private collectors and sold for thousands of dollars at some auction or used as a doorstop or a paperweight, but instead are exposed just as one of the few working paleontologists in the world happens to walk by -- well, we're lucky that the known fossil record is as good as it is. Remember that even if only *ONE* transitional fossil were known, it would be a tremendous support for evolutionary theory. (Thus the tremendous impact of _Archeopteryx_ in 1861). We now know of HUNDREDS of transitional fossils. It is logically absurd to demand that a *particular* gap be filled, and if it can't be filled to then say that evolution has been falsified -- meanwhile ignoring all the gaps that *have* been filled. I'll leave it at that. This has been a partial list of transitional fossils among some of the major taxa of vertebrates. This list has been brought to you by the numbers 1 and 7 and the letter E. BIBLIOGRAPHY "Chinese bird fossil: mix of old and new". 1990. Science News 138: 246-247 [this fossil was described at the 1990 annual meeting of the Society of Vertebrate Paleontology, so there's probably a paper on it in the collected meeting papers.] Colbert, E. 1980. _Evolution of the Vertebrates_, 3rd ed. John Wiley & Sons, New York. Gould, S.J. 1983. _Hen's Teeth And Horse's Toes_. W.W. Norton, New York. [The title essay discusses evidence that some species retain old genes for traits that they no longer express -- teeth in chickens, side toes in horses. ] Feduccia, A. 1980. _The Age Of Birds_. Harvard University Press, Cambridge, Mass. Gingerich, P.D., Smith, B.H., Simons, E.L. 1990. Hind limb of Eocene _Basilosaurus_: evidence of feet in whales. Science 249:154.


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