Darwin's Predictions
The pentadactyl structure—five digits (four fingers and a thumb for humans) at the end of the limb structure—is one of the most celebrated proof texts for evolution. The pentadactyl structure is found throughout the tetrapods and its uses include flying, grasping, climbing and crawling. Such diverse activities, evolutionists reason, should require diverse limbs. There seems to be no reason why all should need a five digit limb. Why not three digits for some, eight for others, 13 for some others, and so forth? And yet they all are endowed with five digits. As Darwin explained, “What can be more curious than that the hand of a man, formed for grasping, that of a mole for digging, the leg of the horse, the paddle of the porpoise, and the wing of the bat, should all be constructed on the same pattern, and should include similar bones, in the same relative positions?” (Darwin, 382)
Such a suboptimal design must be an artefact of common descent—a suboptimal design that was handed down from a common ancestor rather than specifically designed for each species. And the common descent pattern formed by this structure is often claimed as strong evidence for evolution. (Berra, 21; Campbell et. al., 509; Futuyma, 47; Johnson and Losos, 298; Johnson and Raven, 286; Mayr, 26) One text calls it a “classic example” of evolutionary evidence. (Ridley, 45)
Such a suboptimal design must be an artefact of common descent—a suboptimal design that was handed down from a common ancestor rather than specifically designed for each species. And the common descent pattern formed by this structure is often claimed as strong evidence for evolution. (Berra, 21; Campbell et. al., 509; Futuyma, 47; Johnson and Losos, 298; Johnson and Raven, 286; Mayr, 26) One text calls it a “classic example” of evolutionary evidence. (Ridley, 45)
But this prediction is now known to be false as the digit structure in the tetrapods does not conform to the common descent pattern. In fact, appendages have various digit structures and they are distributed across the species in various ways. This is found both in extant species and in the fossil record. As evolutionist Stephen Jay Gould explained, “The conclusion seems inescapable, and an old ‘certainty’ must be starkly reversed.” (Gould)
This means that evolutionists cannot model the observed structures and pattern of distribution merely as a consequence of common descent. Instead, a complicated evolutionary history is required (Brown) where the pentadactyl structure re-evolves in different lineages, and appendages evolve, are lost, and then evolve again. And as one recent study concluded, “Our phylogenetic results support independent instances of complete limb loss as well as multiple instances of digit and external ear opening loss and re-acquisition. Even more striking, we find strong statistical support for the re-acquisition of a pentadactyl body form from a digit-reduced ancestor. … The results of our study join a nascent body of literature showing strong statistical support for character loss, followed by evolutionary re-acquisition of complex structures associated with a generalized pentadactyl body form.” (Siler and Brown)
References
Berra, Tim. 1990. Evolution and the Myth of Creationism. Stanford: Stanford University Press.
Brown, R., et. al. 2012. “Species delimitation and digit number in a North African skink.” Ecology and Evolution 2:2962-73.
Campbell, Neil, et. al. 2011. Biology. 5th ed. San Francisco: Pearson.
Darwin, Charles. 1872. The Origin of Species. 6th ed. London: John Murray.
http://darwin-online.org.uk/content/frameset?itemID=F391&viewtype=text&pageseq=1
Futuyma, Douglas. 1982. Science on Trial: The Case for Evolution. New York: Pantheon Books.
Gould, Steven Jay. 1991. “Eight (or Fewer) Little Piggies.” Natural History 100:22-29.
Johnson, G., J. Losos. 2008. The Living World. 5th ed. New York: McGraw-Hill.
Johnson, G., P. Raven. 2004. Biology. New York: Holt, Rinehart and Winston.
Mayr, Ernst. 2001. What Evolution Is. New York: Basic Books.
Ridley, Mark. 1993. Evolution. Boston: Blackwell Scientific.
Siler C., R. Brown. 2011. “Evidence for repeated acquisition and loss of complex body-form characters in an insular clade of Southeast Asian semi-fossorial skinks.” Evolution 65:2641-2663.
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