Stockholm, Apr 19 (IANS): When early humans turned flesh eaters, the diet allowed women to wean babies earlier and have more children, culminating in the species' global spread, a study reveals.

The findings provide insight into how carnivory may have contributed to early humans populating earth. Comparing 67 mammalian species, including humans, apes, mice and killer whales, among others, Lund University researchers found a clear correlation between carnivory and earlier weaning.

"Eating meat enabled the breast-feeding periods and thereby the time between births to be shortened," said Elia Psouni, from Lund, who authored the study. "This must have had a crucial impact on human evolution," Psouni was quoted as saying in the journal Public Library of Science ONE.

Among natural fertility societies, the average duration of breast-feeding is two years and four months. This is not much in relation to the maximum lifespan of our species, around 120 years, said a university statement.

It is even less if compared to our closest relatives: female chimpanzees suckle their young for four to five years, whereas the maximum lifespan for chimpanzees is only 60 years.

Many researchers have tried to explain the relatively shorter breast-feeding period of humans based on social and behavioural theories of parenting and family size.

But the Lund group has now shown that the young of all species stop suckling when their brains have reached a particular developmental stage.

The difference is that carnivores, categorized as species of whom 20 percent energy content comes from meat, reach this point earlier than herbivores or omnivores due to their higher quality diet.

"That humans seem to be so similar to other animals can of course be taken as provocative," Psouni said.

"We like to think that culture makes us different as a species. But when it comes to breast-feeding and weaning, no social or cultural explanations are needed; for our species as a whole it is a question of simple biology," added Psouni.