A new study has suggested that when breast-feeding human mothers have family support, it may be a key strategy that enables them to reproduce more rapidly than other primates.
According to the study, social support helps mothers conserve energy in a way that allows their bodies to prepare for their next pregnancy.
"Humans out-produce other primates. So we are examining to what degree this is related to our cultural flexibility," said Barbara Piperata, assistant professor of anthropology at Ohio State University and principal investigator of the research.
Breast milk production places huge energy demands on woman's body - an estimated 30 percent increase.
But humans have multiple ways to offset those demands that involve more than just eating more or doing less.
Some studies have suggested the human body becomes more metabolically efficient during lactation, requiring less energy or less oxygen to complete physical tasks.
And new human mothers also tend to have other humans around to share the work burden.
However, nonhuman primates that have similar energy demands while breast-feeding single, slow-growing offspring, don't have that same flexibility.
As a result, their reproductive rates are relatively low, averaging a new birth every four to seven years.
"We know that negative energy balance on the body lowers a female's ability to get pregnant. If humans mediate that, have social support, and are able to maintain or even achieve a positive energy balance, they can get pregnant faster. From an evolutionary perspective and fitness, that's important," Piperata said.
The study was described during the annual meeting of the American Association for the Advancement of Science in Chicago.