Tuesday, September 18, 2007

Evidence for the Evolution of the Brain?

Michael Egnor posted a blog piece covering a claim that links the evolution of amylase enzymes, which are found in saliva, to the evolution of the human brain. It is titled Spit-Brain Research. The following two paragraphs are quoted (in blue):

"Much of recent evolutionary self-satire involves the origin of the human brain. How did an organ of such staggering complexity and biological novelty arise? For evolutionary biologists, no speculation (except design) is too outlandish. Evidence: a paper in Nature Genetics offers a new theory to account for the human brain: spit.

According to the authors, evolution of the human brain was helped along by the evolution of spit, or more precisely, by evolution of the genes that code for the amylase enzymes in spit. Our brains needed a lot of energy, so evolution favored hominids with more effective carbohydrate-dissolving spit."


Worthy of note, from my persective, is the flimsy linkage of a moderate enhancement in the efficiency in carbohydrate metabolism to the evolution of what may be nature's most complex and extraordinary biological feature. While the brain may be an energy hog it is much more. Human intelligence is quite unique and I would be interested in more analysis of the physical pathways said to be associated with a biologically revolutionay adapatation within a time frame that is small by geologic standards. Another quote of Dr. Egnor follows:


"The spit-brain paper no doubt contributes to the literature on salivary amylase. A study of the comparative biology of salivary enzymes- genuine science but with limited (to say the least) popular appeal- would have languished on dusty shelves were it not for the authors’ utterly unwarranted inference that their research is relevant to the origin of the human brain. It seems to be a contemporary maxim in evolutionary biology- ‘attach preposterous speculation about the origin of the human brain to your arcane research, and you’re famous’, at least for a day or two.

Nature recently published an editorial asserting that the inference to design has no place in our effort to understand the origin of the genetic code or the origin of the intricate nanotechnology in living cells. Now, a few months later, Nature lauds a research paper that asserts that groundbreaking insight into the origin of the human brain can be gained by extrapolating from the comparative biology of spit.


Egnor makes a laudable note of Nature's capricious standards of evidence. The saliva inference is generous extrapolation indeed. Yet the obvious design inherent to the genetic code is given short shrift in a petulant Nature editorial. A good example of a mindset influencing the clarity of one's outlook.

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