Taking our (lovely lady) lumps

Of course I'm still talking about our PNAS paper. Wouldn't you, in my shoes?

Since getting the back story, the story, and the implications for your pregnancy out of the way, I can finally talk about some important cultural and philosophical implications of our paper.  

Aw. The poor girl's compromised. 

Are ladies' hips compromised?
Women aren't called broads for nothing. We have, on average, larger dimensions of the pelvis that comprise the birth canal (linked into broader hips) than men do and this is not just relatively but absolutely and this is not just in the U.S., this is species-wide (1).

There is no better explanation for this than it's due to selection for successful childbirth.

But somehow with the combination of classic biomechanical theory, plus obvious performance differences between the sexes, it has become ingrained in our thinking that wider hips make women athletically inferior to men. In this line of thinking, the  male pelvis is the human ideal because it's part of a superior athlete's body. The female pelvis, therefore, is second-rate--compromised for necessary reasons to do with childbirth.

But recent research by Anna Warrener--which she was so generous to contribute to our paper--shows that hip breadth fails to predict the biomechanical values that are used to calculate walking and running economy. There's support, too, from prior studies that used different or less complex models. So the notion that wide hips are worse at walking and running is not supported by current evidence.

He must be the fastest swimmer alive because of his man hips.

Not only does Anna's research call into question whether women's hips are to blame for our failure to dominate sports, but it also lends strength to any doubt that slightly wider hips that could better accommodate a neonate or that could birth a more developed neonate (i.e. one that is more precocial like all the other primates) are being selected against in favor of proper walking and running ability.

Of course, there could be alternative explanations. Selection could be keeping wide hips from getting wider because of some yet to be understood horrible side effect of too-wide hips. It could be that wider hips than we have now would increase the stress on the hips, knees and ankles to the point of immobility. It could mean that the soft tissues of the pelvic floor would be stressed beyond their mechanical properties and strained to failure. It's also possible that pregnancy itself requires a narrow-enough pelvis to carry the fetus above it, and that getting any wider down there in the swimsuit area would mean the fetus literally falls out before it's ready. But to my knowledge, we don't have good understandings of any of this, at least not in evolutionary terms.

Given research like Anna's, it's much harder to support this idea that we're at the perfect balance now in the ladies' pelvis: With pelvic width (despite all the variation) thanks to childbirth keeping it perfectly wide but bipedalism keeping it perfectly narrow.

But that's--as I'm finding more and more with this research--what many people support. There's this thinking that humans are presently at this perfect balance and that everything would fall to pieces if we weren't. From the childbirth side of the scale it's true: Gotta be big enough! (But that's true for all animals that give birth through a bony birth canal.) However, it's not clear why it's true from the bipedalism side of the balanced equation.

And if turns out to be true that narrow hips do not contribute to male domination in sports (assuming male sport domination is on mother nature's radar), then tell me what is ideal about the male pelvis? Maybe you never thought about it that way, but by assuming that the female is compromised, the "ideal" status for males is implied.

Neither the existence of sexual dimorphism in pelvic dimensions, nor anything else that I can think of supports a tradition of placing suboptimal value on the female form. The female births the babies so if (iff) there’s an "ideal" it’s female. Selection maintains its adequacy for locomotion and for childbirth. If it didn’t, humans would have gone extinct.

To some that may still mean the female pelvis is compromised. To me, it's a multi-tasker and a good one.

Always look on the bright side of life. But up to a limit, please. 
A popular reaction to our paper is, But why the tight fit at birth? It's impossible to ignore! Why should childbirth be so difficult?

Answers of "because the baby is big and the birth canal is not" or "it's a coincidence that might mean nothing because clearly we overcome it just fine" or "I like to think it's just a coincidence that my finger fits perfectly into my nostril" ... these sorts of replies rarely appease a protester.

We already discussed adaptationism in this context, but it's fun to consider it further in more Panglossian terms.

When I imagine what it was like to first hear about the obstetrical dilemma back in the 1950s and '60s when it was first suggested, here's what I think my reaction would have been:

Hooray! The pains of childbirth (2) and the curse of helpless babies (3) are no longer Eve's fault but Evolution's! This is great. Eve was framed! Point for evolution AND point for feminism. Woot!

And what I've been yapping away about for four posts is not refuting that evolution's the process behind all this. Of course it is. Everything in biology is either evolution or it's magic.

However, evolution isn't always unicorns and double rainbows. Sometimes life just sucks.

For example, I'm going to die. I could look on the bright side and say that my decomposing carcass will nourish myriad life forms in the complex web of life that lives beyond my death in amazing and beautiful ways. And I often like to think about my molecules living on in a narwhal or a mango tree. But c'mon. Death sucks.

That's an extreme example, but I sense a similar need to make lemonade out of painful and dangerous labor and needy babies.  There must be some good reason...

As if the simple observation ...that childbirth works warts and all... is insufficient reason.

With everyone who was born to a mom who was born to a mom who was born to a mom, etc..., with all the billions of us here today, why are we refusing to accept human reproduction as adequate?

We are nothing less than a raging evolutionary success, just like nearly everything else that is alive right now.

Instead, the downsides to reproduction mean to some that it's deficient, leading them to seek reasons or evolutionary upsides: It's okay ladies, childbirth sucks because humans have such big wonderful brains! It's okay ladies, childbirth sucks so we can walk and run properly! It's okay ladies, babies are so needy and helpless so they get out into the environment where there's proper stimulation for learning and development!

But why do we need any other reason or evolutionary upside than the cute little bundle of joy?

http://blogs.smithsonianmag.com/hominids/2012/08/timing-of-childbirth-evolved-to-match-womens-energy-limits/

References/Notes
1. Simpson SW, Quade J, Levin NE, Butler R, Dupont-Nivet G, et al. (2008) A female Homo erectus pelvis from Gona, Ethiopia. Science 322:1089–1092.

2. The Book of Genesis (See where it all goes wrong after Eve first ate fruit with the serpent then ate it with Adam.)

3. Influential fourth century orthodox Christian, Augustine bishop of Hippo, called upon the fact that infants are born helpless to support his description of the sinful, suffering, terrifyingly vulnerable natural state of the human species. In Pagels, Elaine (1988) Adam, Eve and the Serpent. New York: Vintage.

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And for your Friday happiness...this never fails to crack me up into all kinds of stitches... Jeff Tweedy reads "My Humps" (the song that my title of this post riffs on) by the Black-Eyed Peas.