Natural Science Forum / Biology / Paleontology / February 2005

Taste for meat made humans early weaners
19:00 26 January 2005

Anna Gosline

A taste for meat prompted early humans to wean their children at a young
age. The idea explains why we now wean our infants years earlier than other
great apes.

In non-industrialised societies, women breastfeed their children for an
average of two and a half years, while chimpanzees feed theirs for five.
Anthropologist Gail Kennedy of the University of California, Los Angeles,
US, suggests that humans made the transition to early weaning 2.6 million
years ago.

That was when a branch of hominids began to eat animal carcasses - a risky
activity that would have brought them into contact with other predators and
significantly raised mortality rates for the hunters. This would have
created a selection pressure to wean infants earlier and earlier, since
those no longer dependent on breast milk would have been more likely to
survive their mother's death, says Kennedy.

What is more, the nutritional benefit of eating meat at a younger age would
have helped children's brains to grow and develop more quickly. Human brains
grow three times quicker than those of chimpanzees.

But Barry Bogin of the University of Michigan at Dearborn, US, has a
different rationale for early weaning. He believes it allowed hominid
mothers to have more offspring. "By weaning at 30 months, we have a great
reproductive jump over our closest cousins; we can crank out two babies in
the time it takes a chimpanzee to have one," he says.

Journal reference: Journal of Human Evolution (DOI:
10.1016/j.jhevol.2004.09.005)

Full Text from NewScientist
http://www.newscientist.com/article.ns?id=dn6921