Bony Head Crests in Male Gorillas Shed Light on Early Human Sex Practices

Size matters, if this new study is anything to go by. At least it does in the animal world as scientists discovered that female gorillas preferred mating partners that had larger bony head crests. The new information could shed some light on the social practices of ancient human relatives.

According to a report from the Australian National University (ANU), researchers from the university examined the sagittal crest of four species of apes. The sagittal crest is a bone ridge on the top of their skull. It's been long believed that its function was to provide extra space for the muscles used for chewing, but the team realized that it could also be for sexual selection.

"We found that for male gorillas and orangutans, it is not just chewing that drives crest formation," lead researcher Dr. Katharine Balolia of the ANU School of Archaeology and Anthropology explained. "There is also a social element to it. For example, females prefer male gorillas with larger sagittal crests."

It offers some insight on human relatives because earlier humans also had the sagittal crest.

"And if sagittal crest size and social behaviour are linked in this way, then we could potentially establish that some of our extinct human relatives had a gorilla-like social system," she added. "This would be a first, because otherwise, the human fossil record provides precious little about how our extinct relatives chose their mates."

In gorillas, the researchers found that the crest appears shortly after the wisdom tooth emerges. This fits in with the timing of social dominance or puberty. Orangutans come into their dominance a little later and their sagittal crest also appears later.

The scientists used 3D scans of the skulls to study the crests. As additional evidence for their social function, statistical models also indicated that existing sagittal crests are much larger than they would be if they're only used for chewing.

The findings have been published in the Journal of Anatomy.