Thursday, April 21, 2011

Chimps Give Birth Like Humans, but Don't have Midwives

I can't believe it is almost the end of April! This month totally got away from me. I promise I will make up for the lack of posting soon!

Are humans unique in the way they give birth?

A few months ago I wrote a review of the book Ancient Bodies, Modern Lives by Wenda Trevathan.
This book takes a look at women's reproduction from an evolutionary anthropology perspective

In this review I wrote: 
Trevathan provides a captivating analysis of the medical implications for childbirth of the evolution of bipedalism and large brains and the trade-offs that must be made as a result. Walking upright meant a restructuring of the pelvis, which made it narrower than that of our ancestors and made fitting our larger brains much more difficult during childbirth. Furthermore, the shape of the pelvis changed so that the infant rotates more than once in order for the head and then the shoulders to make their way down into the birth canal. As a result, the baby is born facing the mother’s back, which makes it difficult for the mother to catch her own child without causing damage or death to the infant. Trevathan argues that this accounts for the nearly universal practice of having birth attendants present at birth to assist the mother in catching the baby.
All primates except humans give birth to occiput posterior, or forward-facing, infants, and are able to catch their own newborns. Or so it was thought.

 
It has recently been discovered that this trait of giving birth to occiput anterior infants is not, in fact, unique to humans. An article in Nature Chimps Give Birth Like Humans describes that chimpanzees have been observed giving birth to babies that face the mother's back. This had not been previously known because until now no one had observed chimpanzee parturition, because "they get very nervous" with company around. Probably because the company is some strange human staring at them. I would get nervous, too, if a monkey watched me give birth!

The scientists, who were able to make the chimp comfortable by sleeping in her quarters every night, hadn't even realized that chimpanzees giving birth to occiput anterior newborns was anything special.
 It was only thanks to a discussion with a human-childbirth researcher that the importance of their observations came to light. "She was very surprised to see the orientation of the baby, so we decided to write a paper about it," Hirata says.

The article notes that chimps seek out solitude to give birth to their babies, which the author says "calls into question the argument that backwards-facing babies were an important factor in the evolution of midwifery in humans."

Trevathan says, "I have never said assistance is a necessity in human childbirth, but rather that it's beneficial,"
and she thinks that the pertinent question is not why humans have evolved midwifery, but rather why chimps have not.

From the article:

"It's taken 25 years for people to start reporting some observations that help confirm or refute my hypothesis," she says, "so I'm glad that finally we've got some observational data on chimpanzees — it's advancing science."
 
Trevathan says there are still aspects of human labour that make it "unique, or at least very unusual". "One is the series of rotations that the fetus undergoes as it is born — I'm not sure that's been called into question," she says. "Another is routinely seeking assistance."

She adds that the orientation of the human infant still provides a compelling explanation for the evolution of midwifery in humans because "assistance definitely facilitates delivery when the baby comes out in that position".
If you 'd like to watch the chimpanzees giving birth to their backwards facing babies, which just land on a pile of straw and are then picked up by the mama chimp, there is a link in the article, or you can click this link. Or you can watch it here:



Enjoy!

1 comment:

Leslie said...

I'm no scientist but read lots and remain open to theories of various origins ... would an anterior presentation make sense where the infant is birthed in water? I find the aquatic ape theory interesting (mainly because of a strong attraction to ocean vacations haha!) and having seen water births (videos) of humans, it seems the fat layer (that other infant primates do not have), the substantial vernix, the dive reflex and the fact the umbilical cord continues to supply oxygenated blood until exposed to air, to suggest human infants are adapted to being born underwater. Perhaps the anterior position lends an addition argument for that? It seems all the studies of human evolution are focused on male adaptation whereas the most important aspect of the survival of a species is its reproductive evolution and how that contributes to the success of that species.

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