From: Reuters
Published November 29, 2007 02:08 PM

Male ancestor was slow to grow up

By Ben Hirschler

LONDON (Reuters) - One of our closest ancestors had more in common with gorillas than previously thought, with males of the species taking far longer to reach maturity than females, scientists said on Thursday.

Males of Paranthropus robustus -- an extinct relative of humans that lived almost 2 million years ago -- continued to grow well into adulthood, before a lucky few finally established "harems" of females for breeding.

The result was a big difference in size between males and females.

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"This is exactly what you see in gorillas and a variety of other primates, but not so much in humans or chimpanzees," said Charles Lockwood of University College London.

Although modern human boys do mature later than girls, the difference is small. Male gorillas, by contrast, do not reach full dominant "silverback" status until many years after the females have already started to have offspring.

Experts believe the discoveries about P. robustus will help in understanding how modern human social structures have evolved and pinpoint how reproductive strategies diverged amongst early primates.

The findings, based on an examination of 35 fossilized specimens from South Africa, suggest that life was brutal for young P. robustus males, who faced intense competition as they fought with peers for the right to monopolize groups of females.

"Basically, males had a high-risk, high-return lifestyle in this species," Lockwood said.

"They most likely left their birth groups at about the time they reached maturity, and it was a long time before they were mature enough to attract females and establish a new group. Some of them were killed by predators before they got the chance."

Lockwood and colleagues established differences in size and maturity between different P. robustus specimens by measuring the size and shape of the skull. The age of individuals was assessed by looking at how worn down their teeth were.

Their findings were published in the journal Science.

(Reporting by Ben Hirschler; editing by Myra MacDonald)

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