Chimps emerge from the womb headfirst, just like humans

The longer we watch our primate cousins, the more we realize that all the things that make us uniquely human aren't quite as unique as we thought. The latest discovery reveals chimpanzees give birth in the most human way possible.

Specifically, chimpanzee babies emerge from the birth canal facing away from the mother. In all other non-human primates, the newborns face the mother as they emerge. This positioning is much safer for the baby, as it allows the mother to bring the child closer and clear its breath passage. In humans, our oversize heads mean that fetuses need to twist and turn just to make it out of the birth canal, leading to the unusual birthing position.

Researchers had assumed that only humans gave birth like this, and that the practice evolved in our hominid ancestors as a way of coping with our increased brain size. But now we may have to rethink that, thanks to the recent study from the Hayashibara Great Ape Research Institute in Okayama, Japan. The scientists actually lived and slept with the chimps, just so they could get close enough to witness a birth live and in person.

They witnessed three births, and all of them showed the chimp fetuses emerging facing away from the mother. While the researchers readily acknowledge that these could just be highly unusual exceptions to the general rule, the similarity of the newborns' positions as they emerged suggested that this really is normal behavior for chimps. Researcher Satoshi Hirata explains:

"Anthropologists have argued that the fact that human babies are born facing away from the mothers have led to [the need for] 'midwifery.' But our observation tells us that this is not true. We tend to think that we are unique, without knowing [enough] about other animals."

It's not immediately clear what this all means. There are two possibilities: either chimps and humans evolved this birthing practice separately - unlikely but not impossible - or it goes all the way back to our common evolutionary ancestor, who lived several million years ago. Either way, we're increasingly running out of ways in which humans are unique.

Biology Letters via BBC News.