Evolution and c-sections: are larger head sizes to blame?

I’m a little behind on writing about this article, it has been saved in my inbox for over a month. On February 11th, a brilliant moronic man (is that redundant?) published an article in the LA Times: Considering Evolution and C-Sections: have procedures led to higher birth weight? will they lead to higher IQ?

I teach evolution to my Intro to Human Biology college students. We discuss natural selection… survival of the fittest! Ya know, the Darwin Awards. The idea is that, over time (a very long time), the best traits move on from generation to generation, while the “bad” traits disappear… as the people with those bad traits die off. What are the best traits? Those that ensure reproductive success (usually tied to intelligence, strength, speed, etc.)

An OB at the Univ of Connecticut wonders if c-sections contribute to natural selection… to evolution. Before c-sections, women with complications died during childbirth. Their traits wouldn’t get passed on. So with the advent of surgery, are those previously undesirable traits now being passed on? And succeeding? Are women evolving with a smaller pelvis size and babies with a larger head size?

Oh wait, then he continued on to say that this larger brain size can lead to babies with higher IQ. OMG! Sign me up for a c-section!!!! I NEED A SMART BABY!!!!

PUHHHHHHHHHHH-LEASE.

The article also states that the c-section rate in the US is 15%. Um, I wish. It’s more like 30-35%. It SHOULD be 15%. Where’d he come up with that number?!

At a conference for the American Association of Physical Anthropologists, Chris Stringer and Leslie Aiello gave a presentation. They showed evidence that the (baby) head to (female) pelvis ratio has not changed in 200,000 years and specifically stated that it would have nothing to do with the c-section rate.

Let’s remember that only about 10-15% of c-sections are medically necessary–and don’t get me wrong, I’m extremely glad to have the medical advancements in place for those 10-15% of women that NEED them.

But don’t forget that the rate today is 30-35%. That’s 15-25% of unnecessary cesarean surgeries. That means that about 20% of women with c-sections actually do NOT have a pelvis that’s too small or a baby’s head that’s too large. Therefore they are NOT passing on any of these “undesirable” traits. And even besides that point, evolution takes hundreds of years. How long have we been doing c-sections? About 200. Not nearly enough evidence or research yet to announce something of this magnitude.

And linking it to higher IQ?

PUHHHH-LEASE.

Ryan is a smarty pants. But my husband and I will take the credit for that, thankyouverymuch. 😉

Post-cesarean. Drugged up on morphine, spaced out and cut open. But hey, at least my baby might have a higher IQ!

21 comments to Evolution and c-sections: are larger head sizes to blame?

  • Do you happen to have C-section rates for other developed countries? One of my friends is from South Africa and said the C-section rate there is something like 70%! She said women there regularly choose their child’s birth date. I’m just curious to know how other nations view C-sections what their rates are. Do post if you know/find out.

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    babydickey Reply:

    That’s a great idea, I will definitely research that and post about it!

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  • Beth

    Excellent post, Emily!!!

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  • I was a c-section baby, no wonder I’m so smart 😉

    While I don’t agree with a lot of what the researchers have to say. I have wondered similar things when it came to truly necessary c-sections and evolution. Years and years ago those women and their babies would have died. Now they’re surviving and passing on the traits. To me it totally makes sense that it can effect natural selection/survival of the fittest. Would in a couple hundred of years will we see higher rates of c-sections that are medically necessary because of it? Maybe.

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    babydickey Reply:

    I agree that it’s a possibility… but it’s just way too early to tell. AND only 10-15% of women having c-sections are having necessary ones… and not all of those are because of pelvis size. It’s something like less than 1% of women that actually have that condition.. so for those numbers to rise? For that trait to be passed on and actually have a considerable effect on society? Wayyyyyyyy longer than the 200 years we’ve seen c-sections.

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    babydickey Reply:

    Oops wanted to add – that this is just another way for people to justify the high c-section rate in this country. It’s too high and no one wants to step up and take blame or admit they’re wrong. Blaming evolution of small pelvis size/large head size is just… crazy.

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    Little BGCG Reply:

    It’s absolutely way to early to tell but at some point in the distant future I think it is a possibility that the necessary c-section rate will go up because of it. And not just because of a pelvic size issue. Like I said I don’t agree with the researches about their “findings” but I do wonder what effect necessary c-sections will have on evolution. I do think it’s probable that thousands of years from now the necessary c-section rate could go up.

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  • Sophie Winters

    Where do you get the number that only 15% of cesareans are medically necessary?

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    babydickey Reply:

    WHO (the World Health Organization) recommends a rate of 10-15%, based on what’s actually medically necessary. Also… Healthy People 2010 recommended a reduction in cesarean births in the US to 15% by 2010, which definitely didn’t happen!

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  • That’s really interesting. I agree with you that evolution takes much more time than the conclusion reached would suggest… The premise is logical but it is very early to draw such definitive conclusions.

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  • That is the most ridiculous thing I have ever heard! If this is true, then all 3 of my children are destined to be super-geniuses! I had 3 c-sections. The first was when I was almost 19 and it was an “emergency” c-section. (Although I don’t think there was any emergency that warranted that!) When I got pregnant with my daughter, more than 9 years later, no doctor would even give me the option to try for a VBAC. It is something that in my area they just don’t allow. Basically once you have a C-section, you’re doomed to have repeat sections from there on out. And when I got pregnant yet AGAIN, 3 months after her birth, of course, I had no choice then, either. Having 3 sections was traumatic for me, to say the least. I was panicked the whole time my daughter was being delivered. I am convinced that at least my first 2 sections were completely and totally unnecessary. Thanks for raising awareness on this very REAL epidemic that women must face when they make the decision to trust their doctors and it backfires. To me, this is similar to being raped, in a sense!

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  • I don’t even know where to start. Some researchers are just crazy! I can’t believe an LA Times reporter couldn’t fact check though… too bad the c-section rate isn’t 15%!

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  • The other day, a woman said to me “You had a c-section, right? Because you’re so tiny?” I told her no and that way smaller women than me have given birth to babies way bigger than mine was. Goes to show you how many people can be talked into c-sections by being told that their pelvis is too small. Sad.

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  • erin

    Did anyone on this comment list (or the original blogger) read the article discussed? There is a carefully laid out argument for the proposal that babies will get bigger — because THEY CAN! As long as there is variation in a population, including latent variation towards a small pelvis or a big fetal head, and these traits are heritable, then loss of selection against these traits will increase their frequency. The response to selection is proportional to the heritability times the selection pressure, so if the selection pressure is strong, and now released, evolution can be quite rapid. In the article he cites a 30% decrease in salmon weight in 11 generations due to fishing and keeping only the larger fish. Eleven generations – 30% change in a phenotypic trait! Calculate the number of darwin units there. It’s regrettable that a teacher of evolution argues against an hypothesis she hasn’t even read, using as her argument an argument from incredulity.

    Erin — a high school biology teacher (who has read the original article)

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    babydickey Reply:

    I replied to this comment earlier, but deleted it when I realized you meant the scientific article, not the article I cited. No, I did not read it–if you could post a direct link to a free pdf here, I’d love to read it.

    I know how genetics and inheritance work. I’m not disputing the fact that the change could happen. But less than 1% of women have this condition, first of all… second of all, you can’t dispute the fact that there have been no significant changes in the pelvis size to head size ratio in the last 200,000 years. Maybe head sizes have increased, but then so have pelvic sizes.

    My point is that this is just another ridiculous attempt at justifying the outrageously high c-section rate, which this author wrongly cites as 15%. That would be fairly acceptable, but unfortunately, the rate is more like 30-35%. The author should have done his research so he could at least attempt to sound credible. The c-section rate is too high, due to unnecessary c-sections. To try to blame the rate on “evolution of pelvis size and head size” is asinine. That is my point. Not that changes don’t occur due to evolution and inheritance, because I know well enough that they can and do… it is just NOT the reason for the current out-of-control cesarean numbers and I’m tired of people trying to justify them.

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    erin Reply:

    babydickey,

    The original scientific article is available through your college library, and can be found online as well.

    The original scientific article only pertains to first time moms with a singleton fetus. The primary section rate in this population is around 15% (as of 2008). The author makes clear that there are many other reasons for an increasing section rate, including some that are not flattering to physicians (lack of training, fear of malpractice). But a biologist would also add evolutionary changes to the mix. Head size and birthweight can be measured. Both are heritable and increasing. Stabilizing selection on term birthweight is gone. The maternal pelvis size cannot be measured easily at a population level, but watching a film like Nova’s documentary “A Walk to Beautiful” can tease out the possiblity that sections would allow a woman with a small pelvis to be reproductive, in addition to the terrible consequences of not being able to have a section. This is a 52 minute film, available from Netflix as a disc, and is well worth showing to a biology class. I discuss the C-section article and this film together in my high school class. It also makes the class aware of the horrific health care disparities that exist in the world.

    Another reason for the high section rate is statistical. A woman who delivers triplets (and triplets are all delivered by section) is counted as 3 sections, not one. So a doctor or hopsital that concentrates on high risk pregnancies might deliver one full term vertex baby vaginally and one woman with triplets by section. The section rate for those 2 women is 75% (3 triplets via section and one singleton vaginally). With advanced fertility treatments, there are more multiple births occuring.

    Peace, Erin

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  • erin

    Additional comment — why the male bashing in the second sentence of the blog???? I have 3 sons at home, and it is tough enough to raise responsible young man with all the pejorative images on TV and the popular press. Since when is it OK to call a certain gender, race, or creed moronic??? Grow up, women! Let’s help everyone with their self-image by suppressing our prejudices, so we can have a better world.

    Erin

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    babydickey Reply:

    That’s fair. I was expressing my disgust at the person who wrote this article–as he clearly didn’t do his research and has incorrect facts. It was supposed to be a joke, but I get that it was an unfair generalization.

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    erin Reply:

    If you were talking about the newspaper article, the section rate was I believe misinterpreted, as I explained in the other post. If you are talking about the original scientific article, I only found one mistake, which the author acknowledged when I emailed him. He had the definition of the “darwin” wrong. Even with that said, the number of darwins for a 1% change in birthweight over 20 years is staggering compared to normal rates of evolution. By the way, I wouldn’t blame doctors for the rising birth weights. I would blame the food industry and the people who eat from the food industry spigot, thus becoming obese and diabetic.

    Erin

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  • Ashley

    Haha, dude. You look completely wasted in that picture. Anywho, the guy who wrote that article is so full of sh*t, I can smell it from here.

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