Convergent Evolution and the AAT/H

The Concept of Convergence in Evolution

The AAT/H relies heavily on an important and quite valid evolutionary principle: the principle of convergent evolution. That said, it must also be recognized that the principle of convergent evolution as used in the AAT/H ignores a vital element of that principle. Therefore an explanation of this principle is in order:

From Vertebrate Paleontology and Evolution 1988, by Robert L. Carroll (W.H. Freeman and Company: New York) pg. 7:

"characters that are similar in structure and function but have arisen separately rather than from a common ancestor are termed convergent."
And he uses G.G. Simpson's description of the terms "convergence" and the similar term "parallelism":
"Convergence is the development of similar characters separately in two or more lineages without a common ancestry pertinent to the similarity. Parallelism is the development of similar characters separately in two or more lineages of common ancestry on the basis of, or channeled by, characteristics of that ancestry."

Convergence in evolution (unrelated living things sharing similar traits which they don't share with a common ancestor) is due to a similarity in function in these traits. These are often due, as the AAT/H suggests, to these living things (we'll just consider animals here) living in similar environments which are different from their close relatives. There are classic examples which are often cited, for instance arctic mammals and birds, which often have white coats of fur or feathers, and in the case of mammals, smaller ears to conserve heat. (Conversely, similar animals which live in extremely hot areas often have large ears to radiate heat -- note the difference between arctic foxes and fennec foxes in ear size.) Another environment which creates convergent features is an aquatic one, but unfortunately for the AAT/H, humans share none (!) of the aquatic traits actually due to convergent evolution (take a look at the list in the first 5 "Relevant Questions for the Aquatic Ape Theory").

The essential part of the principle which the AAT/H shies from is that these convergent characters are similar in function as well as in structure. Their similarity in function is what creates selection pressure for similarity in form, so examining and explaining this similarity in function is critical to the appropriate application of the principle of convergent evolution. Perhaps many of the oft-repeated errors by AAT/H proponents arise because they typically present examples of alleged similarity in structure without any examination of function. (Of course when they also present features which aren't similar they compound their errors.)

Why do they make these errors about convergent evolution? I'm not entirely sure, but part of it seems to be a simple lack of understanding of basic evolutionary concepts. It stands to reason that if you're putting together a theory about human evolution, you would learn the basic concepts of evolution (and physiology and other related studies). It's not easy, certainly, but it's not that hard. And it's necessary.