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February 21, 2005

Messed up mouths

"Evolving to Eat Mush": How Meat Changed Our Bodies. This article interviews researchers who argue on the one hand that we are optimized to process and utilize fat and cholesterol in our diet (via meat consumption), and another who suggests that cooking our already tender foods and cutting them up with tools released functional constraints which resulted in the unaesthetic dentition that characterizes humans. As I'm sure many readers know there is already a lot of speculation about the allometry of the human skull and jaw, so this simply opens up another avenue of inquiry. Some might find it of interest that in The Symbolic Species the author makes the case that humans do not have large brains, rather, we have small bodies. In other words our developmental arc is modified from other large mammals in that our bodies are relatively small rather than our cranium and brain being oversized (ergo, freeing up space which doesn't have to manage all that extra muscle and sinew. Though please note that recent evidence mitigates against human brain size being the result of a simple developmental tweak).

Related: Human 'dental chaos' linked to evolution of cooking. AAAS news release on meat.

Addendum: Let me make it clear, the part about processing of fats and cholesterol from meat makes a lot more sense to me than the part about jaws, but remember that evolutionary changes may sometimes be subject to developmental constraints (water can't flow uphill, no matter how convenient it might be), while loss of function might also occur adjacent because of mutations and a lack of purifying selection on that feature. Finally, I have asked about wisdom teeth before in terms of their evolutionary significance.

Update: Also, I remembered this paper which suggests that "that the gene encoding the predominant myosin heavy chain (MYH) expressed in these muscles was inactivated by a frameshifting mutation after the lineages leading to humans and chimpanzees diverged. Loss of this protein isoform is associated with marked size reductions in individual muscle fibres and entire masticatory muscles." They say the mutation appeared ~2.4 million years ago, which would put it somewhat before tool use.

Posted by razib at 02:34 AM