Friday, August 31, 2012

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.


***

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.

22 comments:

Ken Weiss said...

Another fine and thoughtful post, Holly! Of course, behavioral evolutionists will counter (and I think this has been done before, perhaps in the once popular just-so story book The Naked Ape, or some contemporary pop-sci book of long ago), that dames were hippy because it excited men. That is, that this was sexual selection, like other obvious visual traits (Brazilians notwithstanding) that men simply couldn't resist.

So, once one has accepted the 'there must be an adaptive explanation' axiom, they'll have to find it.

Your point that if it works 'Nature' doesn't care how or why (or whether it's fun) is the key point. There may be one or complex or no particular adaptive explanation.

It's just so hard for people to live with that vagueness. We want tidy causal explanations. I wonder why that is?

Perhaps it's because people who had tidy explanations were able to live longer or get mates more easily.....after all, explanations filled with doubts and uncertainties probably did not make for very sexy conversation on dinner dates.

Ken Weiss said...

Oh, and I forgot to mention, for any reader not aware of it, that Holly knows whereof she speaks. She was a jock in her college years, a varsity rower for the Florida Gators. I guess as long as your hips aren't too wide that you can't fit in the boat, women can actually do sports?

Holly Dunsworth said...

Stroke, cox, and bow really have a tight squeeze!

Holly Dunsworth said...

I probably should have written just "selection" and left it at that. Because I honestly don't know how calculations of natural selection on female pelvic dimensions ... those sorts of findings ... are actually distinct from sexual selection. Since we have no data on birth canal size, neonatal size and fitness, over generations, within individuals, that I know of.

Ken Weiss said...

My point was just that sexual selection has been suggested. That just means that, with no functional aspect, if women are more attractive if they are 'broads', they have more kids (that is, even if that has nothing whatever to do with the biology of gestation or parturition etc.).

Some hyper-seletionists would argue that hippiness is sexy _because_ it indicates good motherhood prospects. But such arguments, though common and seen all over the place, professional and popular, is often just guessing.

Holly Dunsworth said...

I know what you meant. It's a famous idea! I was saying very poorly that my post should have accounted for that. I only know of literature that shows (with coefficients of variation, e.g.) that selection has taken place and it's usually framed as natural selection, not sexual.

Ken Weiss said...

Right, but it's also that from a hyper-Darwinist perspective sexual selection isn't just trying to pick up who's hot, but that hot-looking is the signal of top-physical fitness etc. So those arguments try to have it all.

Perhaps, as in a recent paper about horned beetles, and tons of others, the idea is that sexy appearance is for traits that signal health and heartiness.

But who knows, maybe female beetles just like horny males for no other reason!

Ellen said...

Here you go Holly:

http://www.youtube.com/watch?v=pRmYfVCH2UA

-Ellen

patchworkZombie said...

Since there isn't a clear connection to energy efficiency, why do men have such narrow hips?

Holly Dunsworth said...

First, are they "such narrow" to mother nature? And they work great. Why not have narrow hips?

Ken Weiss said...

Geez, Holly, you need to admit what the real truth is: girls simply love those skinny hips. They can't keep their eyes off 'em. They gaze, droolingly, but just don't remark about it (or, perhaps only to each other), the way guys can't help doing when a woman with _her_ natural geometry walks by.....

Holly Dunsworth said...

Slim hips do make the shoulders look broad!

Ken Weiss said...

Sorry, Holly. But for decades I've been reading definitive books on human sexual dimorphism, and you can't get away with the distracting tactic of claiming that all women care about is 'shoulders'.

At least men, perhaps crudely but honestly, admit what they're admiring. The idea that big shoulders mean He is a hulking brute who can go out and get the wildebeest is one possible excuse for sexual selection, but it's lame.

Actually, I thought you might say that all women pay attention to is whether men would be good, sympathetic listeners and helpful partners. So I was eager to see how you were going to try to relate that to slim hips....

Holly Dunsworth said...

Slim hips offer another kind of optical illusion that anybody who's reading this with a gutter mind has probably already thought of by now.

Ken Weiss said...

Gutter-minded? But this is about evolution! Survival of the species! The only thing that's important in life! At least, that's what Darwinian viewpoints say.

Holly Dunsworth said...

Slim hips may indicate no eggs, so don't spend your evenings courting and don't send your swimmers to die on a wild goose egg chase. Slim hips really help men see who NOT to focus their attention on. Wide hips would be nothing without slim ones.

Holly Dunsworth said...

Now that quotes have been lifted from my blog posts and posted in stories elsewhere I have queasy feelings about leaving brainstormy or silly or sarcastic comments out in public... all vulnerable to being read as fact. Oh well. It's not going to completely stop me from having fun.

Anonymous said...

If narrow hips don't offer an advantage in athletic-based locomotion then why do all great female athletes have narrow hips? Ever look at distance runners and sprinters?
There's no reason a female soccer player should suffer more ACL tears since she's lighter and has less upper body mass and leg strength closer to the male average compared to upper body strength.
I don't think anyone ever said narrow hips are the sole reason males dominate sports in general and dominate even sports that require little explosive strength like distance running, just that little differences in efficiency make a big difference when you run 26 miles.
People were actually predicting females overtaking males in stamina sports in the future. Few are predicting that now that the science of sports physiology has matured. Men have longer levers, bigger hearts and lungs, higher carrying-capacity of Oxygen, and narrower hips. At the elite level, a deficit in any one of those factors can have a huge effect.

When Edward O. Wilson said the female world champions in running events wouldn't even place in a regional male track meet, he got flayed alive by female faculty at Harvard and by the press. It was true then and even more true now.

Holly Dunsworth said...

Sorry if I gave the impression that narrow hips do not aide performance. That's not the point. The point is to reveal what has been biasing our view of the evolution of the pelvis, of sexual dimorphism, and childbirth all coming together to explain "early" birth. And I have yet to see anyone make a good argument that performance differences among humans today is a useful evolutionary model for selection pressures through hominin history or today. In addition, ACL tears have not been shown to be linked to wide hips.

Holly Dunsworth said...

Maybe my post wasn't as clear as it could be because it's part of a series of posts on the obstetric dilemma where I lay out quite a lot of the ideas and where I'm coming from.

Holly Dunsworth said...

Thoughts on the performance gap between men and women. I don't see it ever being equal and I think that's a sound prediction based on what we know about biology. However, I don't blame women today for still being sensitive about this issue. My mother made the USA Junior Olympic track and field team but her parents didn't support a girl's athletic ambition so she couldn't attend. I passionately loved soccer as a kid and saw other schools in our division/region allowing girls onto the boys team (nobody had a girls team) and as a shy little girl I mustered up the gumption to actually ask our coach if I could too. He told me that if I played soccer with the boys (something I did every day after school), I'd maybe get hurt and not be able to have kids when I grew up. So, 'no.' That was around 1989. I'm 36. These old ideas and the resentment they cause aren't likely to just disappear.

Holly Dunsworth said...

...anytime soon.