June 22, 2009
Social Competition Drove Human Brain Evolution?

We have bigger brains mainly as a result of competition with other humans in more densely populated areas?

COLUMBIA, Mo. - For the past 2 million years, the size of the human brain has tripled, growing much faster than other mammals. Examining the reasons for human brain expansion, University of Missouri researchers studied three common hypotheses for brain growth: climate change, ecological demands and social competition. The team found that social competition is the major cause of increased cranial capacity.

To test the three hypotheses, MU researchers collected data from 153 hominid (humans and our ancestors) skulls from the past 2 million years. Examining the locations and global climate changes at the time the fossil was dated, the number of parasites in the region and estimated population density in the areas where the skulls were found, the researchers discovered that population density had the biggest effect on skull size and thus cranial capacity.

"Our findings suggest brain size increases the most in areas with larger populations and this almost certainly increased the intensity of social competition," said David Geary, Curator's Professor and Thomas Jefferson Professor of Psychosocial Sciences in the MU College of Arts and Science. "When humans had to compete for necessities and social status, which allowed better access to these necessities, bigger brains provided an advantage."

Was a better ability to deal with other humans or a better ability to deal with the rest of reality the primary driver of rising human intelligence for most the last couple of million years? Also, was there a shift in relative importance of various selective pressures over time? The the huge human evolution acceleration of the last 10,000 years suggests that either new selective pressures showed up or some existing selective pressures intensified.

Share |      Randall Parker, 2009 June 22 11:57 PM  Brain Evolution

Grim said at June 23, 2009 7:54 AM:

We started running out of animals to kill 10,000 years ago. Men had become so good at hunting that they where literately depopulating the countryside. That lead to the rise of farming and with it, wealth.

kurt9 said at June 23, 2009 8:27 AM:

Intelligence evolved so that we can better fool and take advantage of each other. This is the message you get if you read between the line while reading Nicholas Wade's book "Before the Dawn".

Lono said at June 23, 2009 11:48 AM:


You seem to imply that an increased ability to manipulate others is inherently an ammoral or even immoral capability.

I would argue that thoughtful manipulation of the masses can serve as a powerful and positive organizing force in civilization.

The problem we find ourselves in now is that intelligent but overly aggressive and unempathetic phenotypes have currently risen to the top of many of the world's power structures.

This can be remedied by replacing them with more intelligent and empathetic but somewhat less aggressive phenotypes.

I would even argue that even more intense selective pressure is now favoring highly intelligent and empathetic but somewhat less aggressive phenotypes as altruistic behavior helps to stabilize Humans living in high density areas.

I believe you will be pleasantly surprised by the outcome of this current Human experiment!


PRB 214 said at June 26, 2009 2:38 PM:


1. Unempathetic types aren't held back by empathy. Especially at the top of the social ladder, the unempathetic types (often psychopaths, sociopaths, or narcissists) still likely reproduced and have sufficient wealth to make sure their offspring pass their genes to the next generation. This is especially relevant when you consider that wealth, power, and domination are so often aphrodesiacs (especially for women).

2. Humans are easily impressed with not only wealth, power, and domination ability, but also charisma and other traits easily confused with leadership. That's another reason so many unempathetic people rise to the top.

Furthermore, the unempathetic types themselves are master cons, manipulators, bullies, and puppetmasters. Together with their charisma or intimidation abiities, they are at an advantage when it comes to persuading the majority to go along with them; not to mention acquire mates. To cure the disease, we have to have enough people admit that there's a disease in the first place. Unfortunately, most of us aren't willing to see the basket of "leadership traits" (in the Stone Age sense) as maladaptive to this era in which progress comes about by intrinsic creativity and "building a better mousetrap". This will require a radical paradigm shift sustainable over several generations AT MINIMUM.

RESULT: It will be a LONG LONG time, if ever, before we/ evolution purges from our genes our unwitting admiration /sexual desire for "The Big Man" or other popularly defined "Alpha" types.

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