July 17, 2014

Craniofacial feminization and the origin of behavioral modernity

Current Anthropology Vol. 55, No. 4, August 2014

Robert L. Cieri et al.

Abstract:

The past 200,000 years of human cultural evolution have witnessed the persistent establishment of behaviors involving innovation, planning depth, and abstract and symbolic thought, or what has been called “behavioral modernity.” Demographic models based on increased human population density from the late Pleistocene onward have been increasingly invoked to understand the emergence of behavioral modernity. However, high levels of social tolerance, as seen among living humans, are a necessary prerequisite to life at higher population densities and to the kinds of cooperative cultural behaviors essential to these demographic models. Here we provide data on craniofacial feminization (reduction in average brow ridge projection and shortening of the upper facial skeleton) in Homo sapiens from the Middle Pleistocene to recent times. We argue that temporal changes in human craniofacial morphology reflect reductions in average androgen reactivity (lower levels of adult circulating testosterone or reduced androgen receptor densities), which in turn reflect the evolution of enhanced social tolerance since the Middle Pleistocene.

Link

11 comments:

Rokus said...

I hope people will understand that any involvement of genetic content located on the modern human YDNA would rip apart current assumptions of neutral inheritance and thus invalidate all existing assessments on a phylogeny-based geographic origin. All the contrary, surviving ancestral haplogroups would reduce to nothing but isolates reminiscent of early expansions, far away from the centres of evolutionary change.

Ed said...

How sure can we be that the feminization of the skull is associated with social tolerance? Can we be sure that this reflects some innate "evolution towards tolerance" rather than just people learning to live in a state society rather than a tribal one?

andrew said...

The paper's conceptual link from facial morphology to androgen levels to sociology is clever and quite plausible and provides real insight. It is nice to see this kind of analysis in the midst of a sea of brute force data analysis papers without the same kind of cross-disciplinary connections and analysis.

Paul White said...

@Rokus:

But couldn't something on the X work to similar effect?

Dobba Makale said...

Sorry for asking a question that is out of topic. What groups of Caucasian people that have skull that is longer, larger, broader and more robust than the skull of Eskimo people?

sykes.1 said...

Wasn't neoteny (juvenalization) supposed to do the same thing? Or is feminization part of neoteny?

Grognard said...

Well this link to testosterone levels is obviously wrong. I don't feel like going into detail but you can tell that by looking at people today alone, or by looking at neanderthal morphology OR by looking at people today who have neanderthal-derived androgenic receptors.

Just fanciful crap to try to make such a claim. Gracility is more complex than that, and neoteny does not equate to greater brain power! If anything probably the opposite, just look at pygmies. Period. Exclamation point.

Grognard said...

Dobba - most nordic people have a long skull and large cranium. Generally speaking more robustity leads to longer skull type. However brain shapes vary as well and the skull conforms to the brain, so some gracile people are also long-headed. In short, all the combinations of gracile and robust people with all kinds of culture and brain size exist so the study is pretty much just fantasy.

Unknown said...

"We argue that temporal changes in human craniofacial morphology reflect reductions in average androgen reactivity (lower levels of adult circulating testosterone or reduced androgen receptor densities), which in turn reflect the evolution of enhanced social tolerance since the Middle Pleistocene. "

First, what is the evidence again for "enhanced social tolerance since the Middle Pleistocene" -- please don't say Pinker.

Second, what is the evidence that higher levels of testoserone or androgen causes less social tolerance?

Third, how would individuals be selected on this basis -- presumably there is some way of telling that has something to do with social tolerance in the middle paleolithic.

Fourth, could it be that there are obvious ways to see the advantage of social tolerance that don't require such sophisticated selective breeding?

Simon_W said...

@ Rokus

The change cannot be ascribed to the y-chromosome alone, because the women obviously got more feminized, too.

@ Dobba Makale

See Coon's map of the head sizes:
http://www.theapricity.com/snpa/bilder/troe-map7a.jpg

According to Coon, the inhabitants of the isle of Fehmarn, just off the coast of northeastern Germany, have particularly large heads: "It is safe to predict that no regional population of any numerical size will be found on the continent of Europe which will exceed the cranial and facial dimensions of the Fehmarners."

I don't know though if they exceed the Eskimo people.

Grey said...

@Unknown

"Third, how would individuals be selected on this basis -- presumably there is some way of telling that has something to do with social tolerance in the middle paleolithic."

Replace "tolerance" with levels of aggression and it makes more sense.

Say for the sake of argument high aggression selects against itself in various ways (e.g. risk taking behavior) and is only net positive when the environment is particularly violent i.e. high aggression can be net positive in a violent environment or net negative in a peaceful environment.

Then if aggression is related to skull shape (due to testosterone levels in the womb) then in more violent environments the women who preferred archaic skulled men would end up having more surviving children and in a more peaceful environment the women who preferred less archaic skulled men would have more surviving children.

As it could swing back and forth with changes in the environment it would make quite a flexible mechanism.

There might be both male, female and autosomal components to this i.e. a population base level with potentially both male and female adaptations to adjust that base.