![]() They scientists said if the timing of crest development is associated with "intense intrasexual competition" among male primates (where members of the same sex compete for mates), we could look back to the fossil record to see if a similar picture emerges among our extinct ancestors that also had sagittal crests. These include Paranthropus robustus, Paranthropus boisei, Paranthropus aethiopicus and Australopithecus afarensis. Some hominin species also have sagittal crests. However, they believe the findings could shed light on the social structures of extinct hominin species. They team says that while their findings support the hypothesis that sexual selection plays a role in their formation, "to what extent sagittal crests may serve a direct function in social signaling" is unclear. "In contrast, in orangutans some males only become dominant quite late in their adult life, and the sagittal crest appears later." We found the sagittal crest appears right after their wisdom teeth emerge, so that fits in with the timing of social dominance," Balolia said in a statement. "In terms of gorilla social structures, the males establish dominance shortly after their wisdom teeth emerge. ![]() Researchers also showed that female gorillas prefer males with larger crests. ![]() The team argues that the timing of the emergence of the crest-when the species reaches sexual maturity-supports the sexual selection hypothesis, where a trait evolves because of a preference for certain characteristics. In Bornean orangutans, males get their crest in mid-adulthood during a secondary growth spurt. In most male gorillas, the crest emerges in early adulthood, while any females with one seemed to develop it more gradually. Their findings showed that in male gorillas and orangutans, the need for larger chewing muscles alone could not explain crest formation. They also looked at both males and females to see if there was a difference between the sexes. They looked at the size of the crest and compared it to dental maturity and at what stage in life the crest develops. In their study, the team analyzed 3D scans of the skulls of four ape species. While our jaw muscles end just below the ear, in a species with a sagittal crest they would extend all the way up, giving them the extra power they need to eat.īut the researchers say this is not the whole story. Modern humans do not have sagittal crests because we do not have to chew tough foods like apes do or our ancestors did. In a study published in the Journal of Anatomy in April, researchers led by Katharine Balolia, from the Australian National University, examined the sagittal crests-a bony arch at the top of the skull-of great apes and gibbons. Researchers claim the crest-shaped bony ridge seen in some species' skulls could be the result of sexual selection-and identifying similar crests in our early ancestors could reveal on how they interacted, especially when it came to social hierarchies and mate selection. ![]() By analyzing the skulls of male gorillas and orangutans, scientists are learning about the social structures created by our extinct hominin relatives.
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