After the switch to an upright posture, probably the biggest single anatomical change on the journey from apes to humans was the weakening of the jaw. In apes, the jaw is large and protrudes way beyond the nose. It is attached by muscle to a bony ridge on the top of the skull and has a force many times that of a human jaw. Recent genomics research has shown that a large mutation about 2.4m years ago disabled the key muscle protein in human jaws. We still have the disabled protein today, and that weakened jaw enabled a raft of innovations. The ape brain could not grow because of the huge muscle load anchored to the skull's crest, and apes cannot articulate speech-like sounds because of the clumsy force of their jaws. This mutation allowed the increase in human brain size and the acquisition of language.
But why did it happen? Wrangham maintains that it was cooking that led to the change. Cooked food does not need strong jaws. In genetics a function that becomes redundant always leads to the gene being disabled by mutations. Around 2.4m years ago an ape switched to mostly cooked food. In the fossil record, a new proto-human appeared 1.8-1.9m years ago: Homo erectus had a much larger brain and no crest on the skull, indicating that the weakened jaw muscle was now standard.
Read the rest over at the Guardian. I don't agree with all the author's conclusions, but I do find it of interest that many, many theories of human evolution are constantly being advanced. Recent genetic research seems to be offering new avenues for helpful guesses at the prehistory of homo sapiens, and it is fun to stay in the discussion on terms other than one's own. Thinking about things in a way different from my own certainly does assist in the ongoing task of broadening the mind.
h/t AL Daily
In other news, I've settled on the blog header that does the job right, and I'm sticking with it. Possibly for months.
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