August 09, 2014
Natural Selection For Less Aggression Enabled Complex Societies

In order for human societies to grow in complexity and sophistication humans first had to evolve to become less aggressive. A greater capacity for cooperation was needed. Well, 50,000 years ago human skulls developed more rounded appearances with and brows became less heavy. Technology boom 50,000 years ago correlated with apparent reduction in testosterone

DURHAM, N.C. -- Modern humans appear in the fossil record about 200,000 years ago, but it was only about 50,000 years ago that making art and advanced tools became widespread.

A new study appearing Aug. 1 in the journal Current Anthropology finds that human skulls changed in ways that indicate a lowering of testosterone levels at around the same time that culture was blossoming.

I've been reading a lot of books lately on rises and declines of great civilizations. I've wondered whether a large scale settled society selects for less aggressive males which eventually makes it vulnerable to being overrun by a neighboring society that is less civilized. Take the Roman Empire for example. Were the Romans of 100 BC a more genetically masculine people than the Romans of 400 AD? Did their own success and long period of fairly safe living set them up to be overrun by genetically more masculine tribes sweeping down from northern Europe?

Cooperative temperaments are needed for larger scale human undertakings.

"The modern human behaviors of technological innovation, making art and rapid cultural exchange probably came at the same time that we developed a more cooperative temperament," said lead author Robert Cieri, a biology graduate student at the University of Utah who began this work as a senior at Duke University.

Lowering blood testosterone wasn't the only way this change could have come about. Testosterone binds on many receptors and activates many genetic regulatory systems. Lots of different places in the genome could have mutated to modify the effects of a given level of testosterone.

The study, which is based on measurements of more than 1,400 ancient and modern skulls, makes the argument that human society advanced when people started being nicer to each other, which entails having a little less testosterone in action.

Heavy brows were out, rounder heads were in, and those changes can be traced directly to testosterone levels acting on the skeleton, according to Duke anthropologist Steven Churchill, who supervised Cieri's work on a senior honors thesis that grew to become this 24-page journal article three years later.

Some features of the masculine mind (e.g. greater ability at spatial reasoning) would have remained advantages in some ecological niches. Especially before settled agriculture spatial reasoning would have enhanced hunting performance and therefore food supply.

After 150,000 years humans went thru a technological renaissance. The Upper Paleolithic was getting old and it was time to start preparing for the Middle Paleolithic. Sure, it was cold in the Ice Age. But

There are a lot of theories about why, after 150,000 years of existence, humans suddenly leapt forward in technology. Around 50,000 years ago, there is widespread evidence of producing bone and antler tools, heat-treated and flaked flint, projectile weapons, grindstones, fishing and birding equipment and a command of fire. Was this driven by a brain mutation, cooked foods, the advent of language or just population density

What about selective effects for greater intelligence? Could the burst in tools making also come about due to selective pressures for higher intelligence? Maybe formation of tribes which internally had a greater willingness to cooperate created societies where being smart provided a bigger selective advantage. So the greater amount of cooperation created conditions for new selective pressures to emerge.

Another thing I wonder about: How much do variations in facial shapes across the world today represent sexual selective pressures for specific appearances, different selective pressures for masculinity or femininity, or just genetic drift? What are all the reasons why people come in so many shapes, sizes, and complexions?

And then there is my favorite question about human genetics: What happens to future humans when prospective parent start doing offspring genetic engineering? For example, do the girls become more feminine and the guys more masculine? Or do they converge? Do girls become taller? Or more in a narrower height band? What will be the most popular eye color or hair color? Will genetically engineered offspring be more or less cooperative? More or less motivated to work?

Share |      Randall Parker, 2014 August 09 09:37 PM 

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