Primatology.net

Since primate brains and sexual dimorphism are topics that are still fresh on our minds after this morning’s post, I figured I should let you know about a new publication that came out of the open access journal BMC Biology on the differences between male and female primate brain structures and how they developed. It ain’t paleoprimatology in any sense, it’s straight up primtate neuroscience.

In “Primate brain architecture and selection in relation to sex” authors,

“Patrik Lindenfors, Charles Nunn and Robert Barton [we wrote about Dr. Barton before, here] examined data on primate brain structures in relation to traits important for male competition, such as greater body mass and larger canine teeth. The researchers also took into account the typical group size of each sex for individual primate species in order to assess sex-specific sociality – the tendency to associate with others and form social groups. The researchers then studied the differences between 21 primate species, which included chimpanzees, gorillas, and rhesus monkeys, using statistical techniques that incorporate evolutionary processes.”

What they found is pretty important, in my opinion. They have concluded that differences between primate sexes cause developmental effects on the brain, and that is due to different pressures on males and females to keep up with social or competitive demands. From News-Medical.net,

“The authors found that sexual selection had an important influence on primates brains. Greater male-on-male competition (sexual selection) correlated with several brain structures involved with autonomic functions, sensory-motor skills and aggression. Where sexual selection played a greater role the septum was smaller, and therefore potentially exercised less control over aggression.

In contrast, the average number of females in a social group correlates with the relative size of the telencephalon (or cerebrum), the largest part of the brain. The telencephalon includes the neocortex, which is responsible for higher functions such as sensory perception, generation of motor commands and spatial reasoning. Primates with the most sociable females evolved a larger neocortex, suggesting that female social skills may yield the biggest brains for the species as a whole. Social demands on females and competitive demands on males require skills handled by different brain components, the authors suggest. The contrasting brain types, a result of behavioural differences between the sexes, might be a factor in other branches of mammalian brain evolution beyond anthropoid primates, too.”

I’ve bolded the conclusions that I consider the most impacting. While, I’m weary about the how this applies to humans, I cannot deny the correlations the authors have derived. Research like this is fundamental to understanding the physical origin of very complicated social behaviors, and the authors provide us with a map of primate brains and how they correlate to sex related behaviors.

As far as how this impacts humanity — I believe human brain development is much more complex and social issues and culture imprint human brain development to a much greater degree in humans as compared to non human primates. So it’s a bit hard to say, in my opinion again, that this model of sex-selection and number of females really impact the developments of our brains.

From the paleoprimatology department comes news that a second intact cranium of Aegyptopithecus zeuxis has been found and is, ‘”extraordinarily unusual,” …mainly because it’s complete and uncrushed.’ This fossil cranium is important because tells us a lot about what was going on with primate brain evolution many million years ago.

The fossil cranium was found by Elwyn Simons, a primatologist at Duke University, and his colleagues. Aegyptopithecus zeuxis is around 30 million years old and believed to be an old world monkey. From National Geographic News,

“The completeness of the fossil skull allowed Simons and colleagues to take computerized x-rays and create a virtual model of the specimen’s tiny brain.

Based on analyses of previous fossil skulls collected at the dig site outside Cairo…, scientists had assumed the ancient monkey’s brain was larger and more advanced.

The new fossil indicates Aegyptopithecus had a relatively primitive brain compared to its descendants…

Nevertheless, the brain region responsible for vision, called the visual cortex, was large. This suggests that, like many primates, Aegyptopithecus had good vision.”

From the x-ray scan, Simons and team also found out there was a great degree of sexual dimorphism… an anatomical size phenomenon between males and females. In this situation the newly discovered fossil was a ‘female, which may have weighed about 5.5 pounds (2.5 kilograms)’ while the older Aegyptopithecus was a male, twice the size.

Dean Falk, an anthropologist that specializes in primate brain evolution, specifically hominid brain evolution, commented on the finding. She said this finding,

“”challenges “perceived truths” that large brain size was required for things like daytime activity and living in large social groups.

“[The new study] is saying you don’t have increased brain size back when you have some of these things,” she said.

In fact, Falk believes the virtual model of Aegyptopithecus’ brain, used in the new study, suggests the brain was even less advanced than the researchers propose.

However, Falk agrees that the brain model does confirm an enlarged area for vision, suggesting good eyesight was important early on for our ancestors.”

From what I am gathering this is an important conclusion that implies the primate brain expanded vision before it enlarged anywhere else. Of course more fossil primate skulls could support that or show that this feature happened in the Aegyptopithecus lineage.

The results of the x-ray analysis of Aegyptopithecus have apparently been published in PNAS, a journal notorious for letting press releases come out way before the actual publication. That being said, I don’t have a link to the actual publication as of now.