Why is human brain so big? Maybe competition

Questions linger
The social competition hypothesis "sounds good," said Ralph Holloway, an anthropologist at Columbia University, who studies human brain evolution. But, he adds: "How would you ever go about really testing that with hard data?"

He points out that the sparse cranium data "doesn’t tell you anything about the differences in populations for Homo erectus, or the differences in populations of Neanderthals." For example, the number of Homo erectus crania that have been found in Africa, Asia, Indonesia and parts of Europe is fewer than 25, and represent the population over hundreds of thousands of years, he said.

"You can't even know the variation within a group let alone be certain of differences between groups," Holloway said. Larger skulls would be considered successful, but "how would you be able to show that these were in competition?"

However, Holloway is supportive of the research. "I think these are great ideas that really should be pursued a little bit more," he said.

Alternative hypotheses
Holloway has another hypothesis for how our brains got so big. In order for brains to enlarge, they need to have more neuron growth, "and to do that, you have to let the brain grow for a longer period of time," he said. He thinks that perhaps increased gestation time in the womb or increased dependency time of children on adults could be the driving force behind larger brains.

Still other hypotheses look at diet as a factor. Some researchers think that diets high in fish and shellfish could have provided our ancestors with the proper nutrients they needed to grow a big brain.

And another idea is that a decreased rate of cell death may have allowed more brain neurons to be synthesized, leading to bigger noggins.

Ultimately, no theory can be absolutely proven, and the scant fossil record makes it hard to test hypotheses. "If you calculate a generation as, let's say, 20 years, and you know that any group has to have a minimal breeding size, then the number of fossils that we have that demonstrates hominid evolution is something like 0.000001 percent," Holloway said. "So frankly, I mean, all hypotheses look good."

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