Australopithecines such as "Lucy" had long arms and short legs, as seen here in a replica skeleton. Photo: Danrha, Wikipedia
Reading The famous preemie "Lucy" and his relatives had comparatively short legs because it gave them the advantages of fighting. At least the US biologist David Carrier believes that this compares leg length and aggressiveness in today's primate species. Thereby giving a clear trend, the researcher explains: The shorter the legs, the more aggressive the males of the respective species are. He therefore suspects that the firm footing and the low center of gravity of short legs were also decisive advantages for the representatives of the pre-genus genus Australopithecus in combat. Previously, scientists had assumed that human ancestors had mainly benefited from climbing their short legs. The Australopithecines, which included the female skeleton discovered in 1974 and known today as the "Lucy", lived between four million and two million years ago. Although the early humans were most likely able to walk upright, did they still have unusually short legs? Although longer than chimpanzees, but significantly shorter than their descendants, the representatives of the genus Homo. Researchers had previously believed that this body feature has been preserved for almost two million years, mainly because it offered advantages when practicing climbing on the trees.

Although David Carrier does not want to completely rule out this explanation, he does not think it is unlikely? After all, monkeys with the comparatively shortest legs, namely male orangutans and gorillas, spend the least amount of time on trees today. The biologist therefore examined whether primate species, including gorillas, chimpanzees, orang-utans, gibbons, baboons, and meerkats, had an association between leg length and male aggressiveness in females. As a measure of the combat readiness of the males served him thereby the difference in the height and in the length of the canines between males and females? both criteria for which earlier studies had already shown an association with aggressiveness.

The shorter the hind legs of the animals, the more pronounced were the size differences between the sexes, the evaluation showed. This shows that shorter legs are actually associated with increased aggressiveness and therefore probably also the Australopithecus males often fought with each other, so Carrier. However, there are exceptions to the rule: while bonobos have shorter legs than chimpanzees, they are more peaceful, whereas humans have longer legs but are more aggressive. In those cases, Carrier explained, there may have been another leg-length factor more important to survival than the benefit of fighting.

David Carrier (University of Utah, Salt Lake City): Evolution, Vol. 61, p. 596 ddp / Ilka Lehnen-Beyel advertisement


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