Humans Are Evolving

The team studied 2238 women who had passed menopause and so completed their reproductive lives. For this group, Stearns’s team tested whether a woman’s height, weight, blood pressure, cholesterol or other traits correlated with the number of children she had borne. They controlled for changes due to social and cultural factors to calculate how strongly natural selection is shaping these traits.

Quite a lot, it turns out. Shorter, heavier women tended to have more children, on average, than taller, lighter ones. Women with lower blood pressure and lower cholesterol levels likewise reared more children, and – not surprisingly – so did women who had their first child at a younger age or who entered menopause later. Strikingly, these traits were passed on to their daughters, who in turn also had more children.

If these trends continue for 10 generations, Stearns calculates, the average woman in 2409 will be 2 centimetres shorter and 1 kilogram heavier than she is today. She will bear her first child about 5 months earlier and enter menopause 10 months later.

More here. And this is just for the few parameters tested in this study; no doubt many more features are evolving as well.

Our culture respects taller thinner women who wait longer before having kids, but in fact we are evolving short heavy women who have kids earlier.  Shades of Idiocracy – in many ways we are evolving to become less of what we now respect.

In principle humans could implement strong central regulations to ensure that they evolved to become the sort of creatures they respect, at least regarding a few features of regulatory focus.  But it is far from clear that we are willing, or even able, to achieve this.  And it is far from clear to me that we would be better off achieving such far ideals. Perhaps short plump early moms are happier, after all.

Of course I expect that within a century the main dynamic will be even faster robot evolution, but the same principle will apply – without strong central coordination they are unlikely to evolve to become what we or they most respect.

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  • When my wife was studying geology, I learned that the vast majority of erosion is caused by very infrequent but severe events (like flash floods), not by the drip-drip-drip of everyday weather.

    It hardly seems surprising that reproductive frequency is correlated with heritable characteristics (which seems to be all the study shows). But the 10-generation forecast doesn’t seem to be worth much. One epidemic, war, genocide or other very infrequent event could easily swamp the drip-drip-drip of everyday procreation.

  • David J

    How can this research be reconciled with the many studies showing that humans are getting taller each year?

    For example, based on quick searching, this this and this.

    Are those upward trends all the result of economic factors, and once we control for those, people are actually getting shorter?

    Can it be that, in each generation the shorter people tend to have more kids, but those kids tend to be taller than their parents?

    • Bellisaurius

      Better food eaten by immigrant populations, with their kids being taller than themselves? If this theory’s true one would probably see the biggest effects in the countries most immigrated to.

  • gfdsxvnhyoh.hhkhhhhhhhhhhhh

    • The following was the opinion of my 3 year old son. It does not necessarily reflect my opinion

  • Kakun

    Shades of Idiocracy

    Perhaps even more literally than you meant it: according to this related article on recent evolution in humans, our brains are shrinking.

    “When it comes to recent evolutionary changes, we currently maybe have the least specific details with regard the brain, but we do know from archaeological data that pretty much everywhere we can measure — Europe, China, South Africa, Australia — that brains have shrunk about 150 cubic centimeters, off a mean of about 1,350. That’s roughly 10 percent,” Hawks said.

    This decrease, despite the increase in measured IQ, seems a good analogy to the selection against height being swamped by the environmental factors allowing for increased height.

  • sabril

    The article seems to be ignoring that evolution can take place in more than one way. Sure, it can be a gradual process where certain traits are more slightly favored with each generation in a population.

    But also situations can arise where one sub-population grows rapidly in numbers and then displaces other sub-populations.

    If you want to know the future of Middlesex County, Massachusetts, you might be better off looking at what’s going on in Dade County, Florida; Rockland County, New York; or Lancaster County, Pennsylvania.

  • Unnamed

    Aren’t these trends smaller than the changes on these dimensions that have occurred over the past century for non-genetic reasons? These data (pdf, tables 7 & 9) contain a 2.3 cm, 11 kg increase over forty years (1961-2001), which suggests that genetic changes are a relatively minor concern (e.g., the women of 2409 probably won’t be shorter than today’s women, despite the genetic changes). Interestingly, two of the genetic trends (shorter height and earlier childbirth) go counter to societal trends and two (heavier weight and later menopause) are consistent with societal trends.

  • The men and women who are most dedicated to status are going to aim for a degree of female thinness which makes fertility less likely.

    It’s not obvious what’s being selected for. Default fatness? A preference for children over status? A generally lower willingness to sacrifice to get status? Difficulty with losing weight?

    • drscroogemcduck

      or it might be short heavy women compete for status in different ways than tall thin women. play games where you have an advantage or less of a disadvantage.

  • Interesting article from timesonline:

    Link – Women are getting more beautiful.

    • Doug S.

      In addition to sexual selection effects, we now have better cosmetics, hair dyes, and even plastic surgery to make women look better than they would through genes alone.

  • Reading recommendation:

    “Natural selection and Social Theory” by the author Robert Trivers

  • I’m not sure that “respect” is the right word for how we view tall, thin women — think of the reaction most people have toward “walking coathanger” models. “Respect” suggests that most people would like to live in a world full of such people — or at least with a lot more than now — in the way that we respect good Samaritans.

    But if you look at who guys actually go ga-ga over, they tend to be average or short, not tall. So unlike fashion models (who guys do not masturbate to), there are very few 5’9″ strippers, porn stars, Hollywood actresses, pop singers, etc. Tall women inherently have less feminine charm than petites.

    You may be right that elite culture producers respect taller women — as they also try to play up the butt-kicking, careerist Amazon — but the masses respect the smaller, more maternal type instead. So, there’s no disconnect between what people respect and who succeeds genetically (w.r.t. female height anyway), but rather a disconnect between who gets respect among the masses and the elite culture producers.

  • What’s the ethnicity effect on this study? Some women could have married Asian, south asian and latin american men and ended up with more children and shorter children.But since the study has been going on since 1848, I would suppose that it does give an indication that shorter women are preferred. Perhaps as society became more industrialized, the advantages of physical size decreased, which made taller women, daughters of taller men on average, lose social prestige because their larger fathers no longer were the most productive members of a society.

    I personally think short girls look like they have a more pronounced waist to hip ratio. .7 WHR on 5 ft looks curvier than .7 WHR on 6 ft.

    • Wild speculation:

      In addition, the physical attributes of men could also play an important role why smaller women are generally prefered. There is definitely a reason, why female porn-stars are usually quite makes the man seem more masculine. Men are not always confident about their own physical attributes (recently, there was an article in a grand German newspaper about it..the percentage of man suffering from this is quite high..),
      this could have macroscopic consequences in consideration of assortative mating.

    • Jake

      That’s1948 – “spanning three generations in some families.”

  • Jonas, that does not explain why people are now becoming genetically shorter than they were before. There is no reason why a male preference for shorer women would have suddenly arisen in the last two centuries. It is possible that the preference was always there but that men were unable to select for it overall. It is also possible that the decline in size has been occuring for many centuries, but that would also require an explanation for why they got tall in the first place and why they keep getting shorter.

  • Uh yeah, hello.

    Women raised on indigenous diets and removed from group television-induced idiocy tended to be more fertile and healthy.

    Doesn’t that apply to everyone??

    Any guy who thinks the runway model 3% body fat look is hot deserves to spill his seed into a barren desert.

  • M

    Did the researchers take into account the fathers’ side of the
    equation? On average, taller men have more children than their shorter counterparts. This pattern among men may well be more
    robust than the reverse pattern among women. If so, then future
    generations may actually become genetically taller. However, insofar
    as inheritance of height is somewhat sex-specific, due to the fact that
    the Y chromosome contains height-influencing genes, future
    generations may become more sex-dimorphic with respect to height.

  • People could also be getting shorter because IQ correlates with height and a relatively higher reproductive rate on the left side of the bell curve correlates with a decrease in height.

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  • Jake

    These guys are making predictions for a time frame which is more than 3 times longer than the entire duration of their study…? Friends don’t let friends extrapolate wildly!

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  • Alan

    Our culture respects taller thinner women who wait longer before having kids, but in fact we are evolving short heavy women who have kids earlier. Shades of Idiocracy – in many ways we are evolving to become less of what we now respect.

    Isn’t this what one might expect – do we not value rarity in most cases. The edges of the curve are always more attractive than the middle – hence the preference for blondes and blue eyes (since these traits are relatively scarce, they represent a premium). So the fact that we respect/value women who delay childbirth and are thinner, may actually be a reflection that they are scarce and becoming scarcer?

  • That humans have continued to evolve is that main point of Greg Cochran & Henry Harpending’s “The 10,000 Year Explosion”. I highly recommend it.

    I hypothesized future sexual dimorphism here.

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