Evolutionary advantage of curves

[DeterminedJuliet]

I had a random thought today.

I've heard it explained that part of the reason why women have curves is because, from an evolutionary perspective, it indicates of host of "status cues" to prospective mates - that they have fat reserves, they're in child-bearing years, they have hips that can easily pass babies, etc, etc.

Today I thought of something I haven't heard before: I was walking with my 18 month old son to the store (he's still very "toddly", but he likes to walk under his own steam for a while, so I usually let him until he gets bored or tired). We went along for ten minutes or so when he started getting too distracted to keep going, so I scooped him up and put him on my hip and kept walking. We were positioned kind of like this:



My son weighs probably close to 35 pounds, which is not a light load to carry with one arm, and after a few minutes I found myself thinking "Wow, I'm so glad I have hips! This would be so much harder if I didn't!" That's when it occurred to me that it could very likely be that part of the reason  women have evolved to have a certain waist to hip ratio is because it makes it a lot easier to carry children for extended periods of time if you have somewhere to "put" them.

Now, obviously, this isn't scientific in the slightest, but I'd be willing to bet that I could carry my son like that for much longer than my husband, even though, conventionally, he's stronger than I am. From an evolutionary prospective it makes sense, as well: which mother/child duo is most likely to survive? A child with a mother who can scoop them up with relative ease and scurry away rather quickly, or a mother who gets tired from having to carry their kid around some other way. Even with the assistance of man-made tools like baby-carrying slings, I still think someone who is naturally "equipped" would be better off.

Anyhoo, my random thought for the day. I did a quick Google search and it doesn't look like there have been any studies related to this, so I'd be interested in what people think.  

[Ecurb Noselrub]

Certainly makes sense, and since that action is pretty universal among women, it seems like it was selected from an evolutionary standpoint.  That doesn't mean that all the other reasons given didn't also play some part, but if little boys were carried on their mom's hips, it sure seems reasonable that they would grow up seeing that as a desirable trait in women. 

[The Magic Pudding]

As apes become more upright and less hairy the carry on back method becomes trickier.
My on shoulder technique has it's perils, low hanging branches, pythons pretending to be low hanging branches.

[Sandra Craft]

Anyhoo, my random thought for the day. I did a quick Google search and it doesn't look like there have been any studies related to this, so I'd be interested in what people think.  

Works for me, esp. since, in a pinch, a woman could grab two kids and run with them and being able to save a "spare" is surely a benefit.

[The Magic Pudding]

Would carrying this way cause back or other problems for the less hippy?
I'm thinking you need to twist yourself to compensate for the lack of hip.  To carry on your back you'd tend to lean forward which might not be good either.

[Tank]

Narrow hips = small pelvic opening = increased potential of birth difficulties.

[OldGit]

I think there's some truth in it.  I could never carry any of mine on my hip; I don't think I ever tried.  Mrs Git did it until they were quite big, and it was very handy.

[Pharaoh Cat]

Anything useful helps when survival is precarious, and if survival is precarious enough and the thing is useful enough, "Houston, we have selection."

The thing originally might have proliferated because it was useful or necessary for a completely different reason.  As Tank has mentioned, the wide hips help with giving birth to what is quite a large dude or dudette for such a narrow escape hatch.  That doesn't preclude the wide hips from being useful for a second reason later.  There are no rules except save your kid from meanies unless you can't, give birth to live offspring unless you can't, mate unless you can't, survive till reproductive maturity unless you can't.  Anything that changes can't to can in any of those four areas will tend to proliferate, and if X does it in more than one of the four, then all the more reason we will see X popping up all over.

X could even have proliferated as a tag-along to Y, where Y helped in one or more of the four areas, and X did nothing, but tagged along as a genetic stowaway, because the genes that give us Y, give us X too, all by accident.  But then the evironment changes, or the creature gets a bright idea, and suddenly X becomes useful.  No longer a stowaway, X starts factoring in as something that helps us save our kids from meanies, or give birth to live offspring, or mate, or survive till reproductive maturity.  Now Y and X are both useful, and are brought about by the same genes.  Boy, will those genes proliferate!

Incidentally, the thing that helps us mate doesn't have to be useful in any of the other four areas.  If male humans, by sheer accident, preferred wide hips in their females, and if mating was competitive enough that only some of the females would ever do it, then wide hips would proliferate, regardless of any other factor, or even in defiance of the other factors, like with the male toucan's ridiculously large beak, or the male peacock's ridiculously attention-grabbing tail feathers.

I once speculated that, since female humans seem to prefer taller men over shorter, all else being equal, then in a jungle where the rest of the proto-human males were still semi-quadrupedal, and thus lower to the ground, the proto-human male who first rose to full bipedalism, and thus stood with head higher up, towering over the other males, would have gotten more chicks, all else being equal, and presto!  Sexual selection for bipedalism.  I actually sent this idea to some scientist, who of course ignored me, because I had no data and no pedigree.

[Jose AR]

Another great topic, thank you DJ!
and pharoah cat, I totally agree with your idea about sexual selection for curves. I've seen all sorts of articles about the male preference for certain face and body shapes. And the curve most mentioned is the hip to waist ratio. recently I've read that there are two schools of thought: that choosing body types/features is really choosing markers for fitness, and that choosing for body features is a positive feedback cycle where the selection has no survival benefit. It is also interesting that is seems that human males seem to select the female, where most mammals have the female doing the choosing. 

maybe holding the toddler on the hip also helps culture, because the child is at the right height and orientation to observe all of mom's movements as she prepares food or talks to others. If this is true it is meme-related, and only seemingly gene related.

[Whitney]

It is also interesting that is seems that human males seem to select the female, where most mammals have the female doing the choosing. 

Even if our ancient history had the males selecting the female (and I can't really picture there ever being a female who would submit to mating with a man she didn't like); the modern dating scene is very obviously mutual (save for cultures who still have arranged marriage).

[Jose AR]

I should have been more clear that it seems men choose women. It is only an appearance that women seem to work to attract men; the reality is far more complex ...

[DeterminedJuliet]

Narrow hips = small pelvic opening = increased potential of birth difficulties.

But saying someone either has "narrow" hips or "wide" hips is a bit misleading. You can't actually see the parts of the pelvic structure that have much to do with delivering a baby. Me, for instance, I'm a pretty "hippy" looking person, but I broke my tail bone delivering my son because my pubic bone was too close to my spine.



The top parts in this picture are mostly what we see of hips, versus the opening near the base of the spine which is where the baby passes. It could have been totally possible for men and women to evolve with the exact same hip "aesthetic", but with women having the wider pelvic opening. If you think about it, from an evolutionary perspective, that would have been the path of least resistance. But instead you see women with a more "flared" and "outwardly hippy" appearance. I think there has to be some kind of external reason for this difference - either, like some other people have said, because somewhere along the way it because a desirable trait for reproduction or because the hip shape itself actually serves some evolutionary purpose (my proposal: carrying young children  ).

[xSilverPhinx]

I'm guessing the advantage in carrying children could have been a piggy-backed trait (or rather piggy-hipped...awful, I know), meaning that it's probably a useful side effect rather than something that actually underwent selective pressure and won the survival game, so to speak. 

But I don't know. I've never heard of that idea before.   

[DeterminedJuliet]

I'm guessing the advantage in carrying children could have been a piggy-backed trait (or rather piggy-hipped...awful, I know), meaning that it's probably a useful side effect rather than something that actually underwent selective pressure and won the survival game, so to speak. 

But I don't know. I've never heard of that idea before.   

I agree, it is most definitely a combinations of factors. I just thought it'd be a neat idea to throw into the mix of considerations 

[Pharaoh Cat]

I just thought it'd be a neat idea to throw into the mix of considerations 

Makes me wish some scientist would start a web site where laypeople could post suggestions for further research.