Smart, weak-jawed humans still make mistakes
The New York Times Magazine section has an interesting article on the evolution of human intelligence (registration required for viewing). The article focuses on a discovery reported last month that geneticists have determined a gene mutation 2.4 million years ago made our human ancestors lose the large strong jaw found in apes and earlier hominids. Those large jaws had required a skull crest to anchor the muscles, and the idea is that losing the jaw and crest made it possible for the human brain to expand. The expanding brain could use tools more readily, so losing the massive jaws needed for eating tough food (and maybe for fighting) was not the disadvantage it would be for a small-brained animal. The rest of the article discusses competing theories for why intelligence evolved in humans.
The mistake, in my opinion, is in this paragraph: The great mystery about all these competing mechanisms is why they should have worked only for humans. We are hardly unique in being a social species; bumblebees, parrots, dolphins, elephants and wolves also live in groups, but none of them have participated in cognitive arms races. Dolphins should not be included on a list of species with small brains relative to humans. Many dolphin species have a brain mass to body mass ratio comparable to humans. It is also unlikely that their brains are simply the minimum size needed to hunt fish. Sharks also hunt fish, and while sharks are highly evolved in their own way (warm-blooded, give live birth instead of eggs), their brains are puny. Something that caused the cognitive arms race in dolphins also needs explaining.
(For more information on the jaw mutation, read Carl Zimmer's website article Chew on This. Something's wrong with his site as I write this, but scroll down to the late March postings, or click here and you should land near the posting.)