A good babysitter can make all the difference — for humans and for chimpanzees.
A new study out of the University of Toronto has found that wild chimpanzee mothers who get help parenting their offspring are able to wean their young earlier and reproduce faster than chimps who go it alone.
The study, published in Royal Society Open Science, looked at 42 pairs of chimpanzee moms and infants at Kibale National Park in Ngogo, Uganda, and compared those who kept their babies close at all times with those who let other chimps hold and carry them.
"The infants that were babysat more had lower nursing rates, and they also were drinking less milk, so this suggests that they were becoming nutritionally independent," lead author Iulia Badescu, a PhD candidate in Evolutionary Anthropology at the University of Toronto, told CBC News. "They were being weaned quicker than infants that weren't being babysat at all."
That meant the mothers had more time to invest in their next offspring, so they reproduced faster, which Badescu says is "helpful from an evolutionary perspective" and "helpful for a species, overall."
Babysitting may not be unique to humans, but it's not universal among chimps either.
Co-operation vs. competition
The world's best known chimpanzee observer, Jane Goodall, found that chimp mothers in Tanzania were very protective of their young — partly because other females were known to steal infants and kill them.
"So one mother's kind of looking around and saying, 'Well there's not a lot of food for all the infants we have right now, so I'm going to kill that other female's infant because I want mine to have resources,'" Badescu said.
But if there's no resource scarcity, the chimpanzees can work together to raise their young.
"At our site at Ngogo, it's a very unusual place because they have so much food and it's so available all year round," she said.
"Because females have food all the time, they don't have to worry about the competition aspect between each other's offspring, so mothers can afford to let others take care of her baby while the mother does other stuff."
Self-care for mothers
The next step, says Badescu, is to figure out exactly how and why this speedy weaning happens.
She has a couple of theories, including one that might sound familiar to human moms: mothers who have babysitters are better able to take care of themselves.
"So if you think that the mother has to hold her baby all the time and she's trying to grab fruit, it might be harder than if she gives the infant to somebody else. Then she's eating her fruit faster," Badescu said.
"That would give her more calories overall, and it would improve her ability to make higher quality milk for her baby. That would help the baby get more calories when it's drinking milk, allowing it grow faster so that it's able to be weaned earlier."