“This [hypothesis] will not stand, man.”
April 1, 2015 5:19 PM   Subscribe

So you'd like to apply an evolutionary hypothesis about gestation to your pregnancy?

"For the past few years I've been challenging the 'obstetric dilemma' hypothesis--the idea that hominin mothers' bipedal pelves have shortened our species' gestation length and caused infant helplessness, and that antagonistic selection between big-brained babies and constrained bipedal mothers' pelves explains childbirth difficulty too. As part of all that, I've been arguing that the historically recent surge of c-sections and our misguided assumptions about childbirth difficulty and mortality have muddled our thinking about human evolution. So, once I was pregnant, you might imagine how anxious I was to experience labor and childbirth for myself, to feel what the onset of labor was like, and to feel that notorious "crunch" that is our species's particular brand of childbirth."

That obstetrical dilemma really tied the room together: Part I, Part II, and the paper: Dunsworth HM, Warrener AG, Deacon T, Ellison PT, Pontzer H. 2012. Metabolic hypothesis for human altriciality. PNAS 109(38): 15212-15216.

"The prolonged period of breastfeeding needed by a human baby is the most energetically demanding period of a female’s life. A mother may even allocate her own brain during pregnancy, losing some 4 percent of its volume, to meet the energetic demands of her baby’s brain. (The loss is regained, fortunately, in about six months.) Some have speculated that the reason female mammals are often much smaller in body size than males is so that the lifetime energetic needs of a female, who experiences metabolically demanding pregnancy and lactation, will equal those of a male."

More from Dr. Dunsworth, including some Evolution PSAs, thoughts on being evolution, and the Human Fossil Record library on Nature.
posted by ChuraChura (29 comments total) 61 users marked this as a favorite
Spoiler alert: Don't worry about it.

(Great post!)
posted by Potomac Avenue at 5:30 PM on April 1, 2015 [1 favorite]

It works if one accepts that late adolescence is the biologically optimal time to give birth. Not that I'd abide such a thing, of course.
posted by Renoroc at 5:30 PM on April 1, 2015 [3 favorites]

Oh my god, I cannot favorite this post hard enough. It looks almost tailor-made to my interests.

BRB, wallowing in links
posted by sciatrix at 5:40 PM on April 1, 2015

This is pretty interesting.

It works if one accepts that late adolescence is the biologically optimal time to give birth.

While it doesn't quite work in today's society, and I cannot speak for women, I would say that early twenties are the best time to be a parent. Imagine having the kids out of the house at age 40 or so!
posted by Nevin at 5:52 PM on April 1, 2015 [4 favorites]

posted by internet fraud detective squad, station number 9 at 6:08 PM on April 1, 2015

Before we get too off track, I don't actually think that is part of Dr. Dunsworth's research. She's speaking specifically about the energetics of each pregnancy.
posted by ChuraChura at 6:09 PM on April 1, 2015 [1 favorite]

The SciAm blog post is really great.
posted by Mei's lost sandal at 6:19 PM on April 1, 2015 [1 favorite]

i personally like the part where the baby eats the mom's brain a little, so many questions have finally been answered.
posted by poffin boffin at 6:59 PM on April 1, 2015 [26 favorites]

Interesting post, I'm curious more about why the ceiling is where is is in terms of 2.1xbmr. Seems like an intense amount metabolic effort.
posted by Carillon at 7:17 PM on April 1, 2015

STAND UP, woman, when birthing your young. It makes a huge difference.
We are bipedal for many reasons. Birthing is one of those reasons.
posted by Emor at 7:18 PM on April 1, 2015 [3 favorites]

Wow, fascinating first link. Off to read the others!
posted by Lexica at 7:30 PM on April 1, 2015

"Part of what has caused many of us to struggle with the OD is that humans do just fine in the face of the tight fit at birth."

Define "just fine"? I suppose the first 26 hours of natural labor were an excellent learning experience (we learned never to try that again!), but without surgical and even post-surgical intervention any one of our kids would have been lethal.

We've stopped rolling the dice after the latest set of complications. Reading about the ~1% terminal failure rate of that last life-saving intervention was terrifying. Of course, ~1% mortality was the average for normal childbirth for most of human history, but as I was just pointing out, different people have very different definitions of "just fine".

Yes, in hindsight it might not be the best idea for a man with 99th-percentile head size and a woman with 1st-percentile body size to fall in love, but here we are.
posted by roystgnr at 7:40 PM on April 1, 2015 [4 favorites]

Just fine meaning... enough people and babies survive for the species to continue making and successfully having more of them.
posted by ChuraChura at 7:49 PM on April 1, 2015 [12 favorites]

I really liked this article, and as a 6-month-pregnant woman dealing with the exhaustion and insatiable appetite of pregnancy right now, a lot of the theory resonated with me. It makes a lot of sense in many ways.

But I wasn't very persuaded by the "just fine" argument in particular.[*] Isn't the point of the OD hypothesis that evolutionary pressures mean that babies are born at around the tightest fit possible that still allows babies to be born? OD doesn't stipulate that we should be dying in childbirth now: it stipulates that if babies' heads got any larger we would all die in childbirth.

[*] I thought the argument that pelvis sizes could increase without causing much difficulty with bipedalism was much stronger.
posted by forza at 8:12 PM on April 1, 2015 [1 favorite]

Not to thread sit, but I think they're arguing that that's where looking at humans within a comparative perspective is useful. There are a number of other primates that have babies born with very tight fits: "let’s not ignore the other coincidences in other primates that clearly aren’t equipped with our bipedal pelvis. What explains their tight fits at birth? Could those explanations apply to humans? That would be the spirit of the [energetics] hypothesis which we have only modeled for humans so far but deserves to be tested by building the same model with other primates."
posted by ChuraChura at 8:24 PM on April 1, 2015 [4 favorites]

The April 1st thing has been driving me CRAZY! This post has made it all better again.

I love you Metafilter. All of you.
posted by Samuel Farrow at 8:24 PM on April 1, 2015 [2 favorites]

I thought this post was about the theory of embryonic recapitulation.
posted by infinitewindow at 8:47 PM on April 1, 2015

My understanding of this theory (obstetrical dilemma) was more like we were still evolving to figure out how best to do big giant skulls and walking up right, so there's some things that haven't been optimized. Like childbirth being dangerous and womens' hips failing at a certain age. And dental crowding. But the article presented it more like "science blames our weird babies on ladies' tiny bones but our babies and pregnancies aren't that weird so let's stop blaming women and our pelvises." I guess there is nothing that the patriarchy can't ruin, even the miracle of human evolution.
posted by bleep at 10:07 PM on April 1, 2015 [2 favorites]

Very convincing with regard to the energy vs. "fit" explanation for the timing of birth. Certainly, the placenta of our late (induced) child was pretty much cactus at the time of birth, which fits with the extreme metabolic demands of late-stage infants.

This part, however, contradicts with what I've been told about human childbirth:

Part of what has caused many of us to struggle with the OD is that humans do just fine in the face of the tight fit at birth. Just because there’s a tight fit, just because childbirth is terrifying, just because it’s not an easy or enjoyable experience, that’s not necessarily a “bad” thing evolutionarily. Clearly it’s the opposite. It’s a good thing. We’re here to think about it! It can’t possibly be “bad” if we keep having babies. The species abides. When you look at childbirth not as a biological failure, or as God’s plague on lascivious women invited by Eve, but when you see it instead as a raging success, the obstetrical dilemma hypothesis is much easier to doubt.

My understanding is that human childbirth is much more fraught than that of other primates. Women (and babies) die all the time during childbirth, and this has been attributed, at least in part, to the physical difficulties in passing through the birth canal. I'm not an obstetrician, though, so perhaps my information is outdated/misinformed.
posted by kisch mokusch at 4:09 AM on April 2, 2015 [2 favorites]

Bleep, that is a pretty reductionist summary of a lot of research which goes far beyond "the patriarchy ruins everything."
posted by ChuraChura at 5:35 AM on April 2, 2015 [1 favorite]

What an interesting post. Thanks, ChuraChura.

The EGG hypothesizes that mothers give birth when they do because they cannot possibly give any more energy into gestation and fetal growth.
Well doesn't that make sense. Very accurate subjective description of last 3 weeks of pregnancy.

A mother may even allocate her own brain during pregnancy, losing some 4 percent of its volume, to meet the energetic demands of her baby’s brain.
Huh. Or rather WAAAAAAH!

The one thing about the OD I hadn't heard of is that female pelves are something of a handicap when it comes to bipedalism, which hardly seems to be supported by observation in any way. As for the female pelvis failing at a certain age thing, do you mean as shown by hip replacement surgery? Because men need those too, and I don't think it has anything to do with angles and structure, rather a tendency towards arthritis.

I don't think I'm convinced by the theory that childbirth used to be easier. Maternal mortality is extremely high in undeveloped nations right now. Historically, just think of all the artists, writers, prominent women known to have died of childbirth or complications, lives cut short mostly in their twenties or thirties. Death in childbirth has been an ever present threat in the lives of women up until very recently. I know the theory touched on in the links is that something about childbirth changed around the invention of agriculture but is that likely, since it's with agriculture that populations started booming? Hard to believe an increased difficulty in childbirth would contribute to that. (A population boom I mean.)

Anyway, reading through the links, the way we've constructed Eve's apple etc as a kind of folk etymology of the OD hypothesis was just echoing through my mind. EGG even seemed jarring in that it bypasses the cultural baggage that comes all wrapped up in OD: WOMEN YOU MUST PAY FOR YOUR CHILDREN WITH WEAK HIPS AND HAVING TO RUN LIKE A GIRL. It was instructive for me at least, to realise how deeply I've internalised some of that stuff.
posted by glasseyes at 7:05 AM on April 2, 2015 [5 favorites]

Pretty reductionist but I don't think its possible for a normal non-genius person to hold a subtle, detailed, nuanced, comprehensive opinion of every facet of social and scientific research ever done and currently underway.
posted by bleep at 7:56 AM on April 2, 2015

Maybe we’re relatively helpless as infants because we can be, that is, because of the relaxed selection afforded by hominin caregivers. Apes are infant coddlers, and assuming our shared ancestors were too, this could have ramped up long ago, with meddling, manipulative parents and alloparents relaxing selection on infant independence, allowing them to evolve paddled feet, weak muscles, fat heavy bodies, and huge heavy heads. A scenario like this would push the origins of helicopter parenting back, potentially, into the Pliocene.

Take that, parenting trend pieces.
posted by emjaybee at 10:26 AM on April 2, 2015 [7 favorites]

Huh! When I was studying anthro, the obstetric dilemma thing was taught as if it were fact.

The one thing about the OD I hadn't heard of is that female pelves are something of a handicap when it comes to bipedalism, which hardly seems to be supported by observation in any way.

The idea is that they couldn't get much wider and still be useful for bipedalism, not that they're currently no good for it. From the article: "the question [is] whether women are presently at an upper limit in pelvic dimensions that selection for bipedalism will allow."
posted by showbiz_liz at 1:19 PM on April 2, 2015

Hold up. "We may have to place some heavy blame on culture for our having it so much harder than chimpanzees"? I'm gonna need way more evidence than 'may' before I believe an argument based on this.

Chimpanzees deliver their babies alone. They just squat down, grab the baby, pick it up, and walk away. Is she really saying that we could do that too if we weren't brainwashed by the media and if we didn't have such a rich diet?

The question of when and how humans developed the practice of assisted childbirth is a huge question in anthropology, because it really does seem to be unique to humans, and every human culture does it, which tends to suggest it's necessary rather than a cultural choice, and that it developed very far back in our evolution.
posted by showbiz_liz at 1:38 PM on April 2, 2015

Assisted childbirth in humans is very common, but it's not uniform. Unassisted/solitary birth persists, and is normative, across cultures and time. Likewise, it's inferring a bit strongly to reduce the statement on cultural influence to a snipe about media brainwashing. Culture includes things like access to anesthetics, which is incentivized by our physiological aversion to pain and our dopaminergic love of relief from pain.

Something I'm surprised to not see mentioned (although I haven't gotten to the last couple links) is the acknolwedgment that all this evolutionary biology is now taking place in an environment saturated with complex mixtures of low concentration synthetic chemistry. We have, what, about 200,000 industrial chemicals right now, real tox data on maybe 2,000 of them, the capacity to assess maybe 100 new chemicals per year with minimal confidence, and a thousand or so new substances added to the industrial profile every couple years. This has led to a very recent and very well-established recognition that we have to invent human-relevant toxicological assessment tools (it's a legitimate paradigm shift that doesn't happen to a field very often), but that's still an acknowledgment that we have no idea what kind of impacts our chemical exposures are having on complex biological processes like gestation and parturition. I'm in toxicology and epidemiology these days, but my academic background's in molecular and evolutionary biology, and this is kind of a big deal right now in all of those areas.
posted by late afternoon dreaming hotel at 2:11 PM on April 2, 2015 [6 favorites]

This is a fantastic takedown. I love, love, love the whole concept because this is one of those fairy tales that lay people and professionals all embraced as fact forever and she just torpedoes it!

Reminds me of when David Graber's Debt came out and he bulldozed the whole barter myth.
posted by latkes at 7:13 AM on April 3, 2015 [1 favorite]

Barter myth? Is this something I have to Google on my own?

posted by Samuel Farrow at 1:02 PM on April 16, 2015

Yeah, it's one of those things that as soon as I read it I was simultaneously like, "NO. WAY." and "DUH"
posted by latkes at 9:56 AM on April 18, 2015

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