This is from the current issue of New Scientist:
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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, 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 (Journal of Human Evolution, DOI: 10.1016/j.jhevol.2004.09.005).

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 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.
From issue 2484 of New Scientist magazine, 29 January 2005, page 17
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Keith