A question on bipedal mammals giving birth (poss TMI)

Inspire by this thread.

When bipedal mammals other than human - gibbons, gorrillas, chimps etc - give birth, in what manner do they do it? Do they do it on their backs, like humans in hospital? On all fours?

I don’t know about apes, but giving birth lying down is not universal in humans either. There are some that claim that squatting is actually a more natural and effective position.

No other ape is bipedal, with the possible exception of the gibbon. They usually swing below the branches, but when the do walk, they tend to walk (or skip along) on 2 legs with their (very long) arms held out (for balance, I would assume).

The forelimbs of gorillas, chimps, etc are not feet.

But they are used in terrestrial locomotion: knuckle walking

And they also mean that apes can presumably “stand” on four points comfortably.

Yeah, they are. Or perhaps more correctly the hindlimbs also terminate in hands. The differences between the terminal part of the forelimb and hindlimb in other apes is about the same as the difference in most other quadripedal species. Both limbs end in flattened appendages with opposable thumbs, broad nails etc.

Of course more pertinent is that fact that other apes (excluding gibbons) walk on all fours most of the time. That makes them quadripedal.

It is common to refer to “arms” and “hands” for all primates. But that doesn’t make them bipedal. It just means they use those arms and hands during locomotion.


Found this.

We now return you to your regularly scheduled nitpick.


Interesting. So does that mean human baby heads are ginormous in comparison to chimpanzee baby heads, then?

A growing body of research supports the idea that lying on one’s back (dorsal lithotomy position) is one of the least optimal positions for humans to birth in. To accomodate the ginormous human baby head, the tailbone actually flexes back out of the way to make more room. If you’re lying on your tailbone, it makes passing the head that much more difficult.

From reading Dr. Sears “The Birth Book,” (IIRC) dorsal lithotomy gained its foothold in the era of “twilight sleep” births when the mothers were mostly unconscious and most babies were extracted with forceps. It makes sense when the mother is knocked out and the doctor needs to maneuver salad tongs.

Dorsal lithotomy isn’t really used all that much, anymore, is it? Every baby book written in the last 15 years, every birth I’ve seen on those weepy cable shows and every birth I’ve attended seems to end up in the semi-upright position - which is also a stupid lousy position, possibly even worse than dorsal. Not only does the semi-upright prevent the tailbone from flexing back, it makes it harder for the pubic symphysis to stretch without separating as well.

Pushing while laying on your side, standing holding a rope or ladder, squatting or sitting in a birthing stool will open the pelvis up significantly - 30% being the number I hear most often quoted by midwives and OB’s. Problem with those positions is that it makes things a bit trickier for the birth attendant.

Of course. That’s what makes human birth so difficult. Our brains are about 3x bigger than a chimp’s. A newborn’s brain is only about 2x the size of a baby chimp’s, and so is relatively undeveloped at birth, even compared to our closest relatives. We continue to grow our brains at an accelerated rate after birth , while chimps (like all other mammals) have a much slower post-birth brain growth rate.

Another difference between humans and chimps is that human babies generally hae to rotate their heads 90 deg to get thru the birth canal, while chimps do not-- they are born face front, in a position that the mother is able to see the face.

It means two things. First, our upright posture means that the birth canal is narrowed; a chimpanzee’s posture allows a larger passageway (relatively speaking). Secondly, our huge brains enlarge the head so that it’s harder for the baby to be born. That’s why we’re born half-cooked according to normal mammal standards; it’s a delicate compromise between bigger brains/upright walking and being born at all. A longer gestation period would make birth impossible and kill too many mothers. Difficult birth is the price we pay.

Wow, I knew human brains grew a lot after birth, but I didn’t know we were already twice as big as a baby chimpanzee’s brain at birth. I thought the second part – having to rotate the head through the birth canal – was a bigger deal. Thanks for quantifying it.

Interestingly (well, to childbirth geeks like me), the anterior position of the fetus is one big reason why humans do much better with an attended birth, rather than going off into the bushes somewhere alone like most animals. If a human is squatting to deliver her own infant and reaches between her legs to catch it and draw it upwards, she can break its spine if it’s in the “correct” anterior position - the spine is not at all limber in extension, even as an infant. She and her baby are much better off if someone else is there to gently catch the baby and bear it downward, or down and back, moving in the direction the spine wants to go. If she’s alone, she’s actually better off pushing the baby towards her back with her hand and letting him drop onto a pile of soft leaves (or a mattress) or something and then picking him up, instead of trying to prevent him from hitting the ground.

Do any other animals assist their females in giving birth?

In some hunter-gatherer tribes women go off alone to give birth. They squat and I guess the baby just hits the ground. If they need to kill it (or them) for whatever reason they do it themselves usually by abandonment.

There are several animal species where other animals will help in giving birth but it’s usually not necessary. For example, female bats give birth upside down (since they are normally upside down by our standards). If other female bats see a female trying to give birth the wrong way they will try to help her.

I mention dorsal lithotomy because of the OP -

A large majority of the population in the US seems to believe that that’s the only way babies come out - on your back in a hospital bed screaming obscenities at the father. I blame television.
I assume the popularity of semi-sitting is because it increases the strength available for pushing (versus lying flat) while still being convenient for the person catching the baby. (no pesky upper leg for someone to hold out of the way while side-lying, more conventional in appearance to all-fours or squatting)

Yes. The other factor is that human babies are most often born face down, with the back of the head presenting first. Other primates are usually born facing forward. That’s why the mother apes, etc can deliver without assistance.