Relaxed selection

In the days of old many kids didn’t make it to adulthood: say 40% among hunter-gatherers. To a a degree, this was caused by genetic load. High mortality purged some of that genetic load, especially to the extent that selection took the form of truncation selection. This process kept mutational load in equilibrium.

In the past century or two, this mortality has become much lower – so this form of selection has become weaker. Mutational load must be increasing. How fast? We will probably know quite soon, from sequencing recent and contemporary individuals. We’ll probably have a handle on the phenotypic impact as well.

In the meantime, we can get a rough idea of the impact of relaxed selection by looking at pioneers, populations that have expanded rapidly in the past few centuries. Some of those populations had a much higher fraction of kids survive than the typical long-term human average: in New England, after he first few years, something like 75% of kids made it to adulthood. This went on for a long time, something like a couple of hundred years – which is why 20,000 Puritan settlers have around twenty million descendants today. Similar things happened with the Quebecois. We know that this relaxed selection among pioneer types left a higher burden of Mendelian disease – not incredibly high, but higher than in similar groups that didn’t undergo a rapid expansion.

How much did this drop IQ? Can’t have been much.

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65 Responses to Relaxed selection

  1. Space Ghost says:

    I’m not smart enough to know if “can’t have been much” is sarcasm, given the recent results that seem to suggest that mutational load has deleterious effects on IQ.

    • gcochran9 says:

      Look at test scores (SAT, PISA, etc) for Yankees, Quebecois. They do fine. Consistent with not seeing noticeable IQ depression in children of older fathers.

      My best guess is that the load at a given moment is N times the amount of de novo mutations per generations, N pretty big.

      • I don’t know nearly as much genetics as I should, so it’s probably due to some simple gap in my knowledge that I’m not sure why you hedged with “my best guess.” Does this mean that there’s a real possibility that mutations are getting purged at very high rates? For N to be not pretty big, a lot of the mutations happening would have to be really bad, right? At least that’s how my non-geneticist mind seems to intuit it.

      • Ruben says:

        There is noticeable IQ depression with paternal age, if you have millions. Carslake et al. 2017.
        I did find paternal age effects on fitness to be somewhat smaller in Québec:
        but I wouldn’t interpret it too much, because there other, boring differences between the samples might explain it too.

    • pyrrhus says:

      SAT tests continue to show a decline of 1-2 IQ points per decade among the major college attending group (most others take the ACT), and in each racial component of the test . The Black/White gap has remained constant. I don’t know of any breakdown in which Yankess or Quebecois could be observed, except by area of the country, But since the relative positions haven’t changed, everyone thinks they are doing fine….Except against the newcomer Asians, who were not thought very bright 70 or 80 years ago, but are now the highest scorers…..Hmm, maybe different selection pressures?!

  2. dearieme says:

    “looking at pioneers, populations that have expanded rapidly in the past few centuries”: wot abaht the Bantu?

    • gcochran9 says:

      A fair question, but he Bantu expansions happened over several thousand years, slower than the examples I was thinking of. I doubt if they experienced low mortality – hard to do, in Africa.

  3. LeeWang says:

    Michael Lynch suggests it is about 1% fitness per generation, and a minimum loss of 1 genetic IQ pt in the last 50 years, most likely more.

    • gcochran9 says:

      If Lynch comes up with an estimate for IQ decline, I couldn’t find it. He cites Woodley and Crabtree, but then, they’re both lunatics.

      That said, Lynch is surely right about relaxed selection having bad consequences. But what’s the rate?

  4. jason says:

    Puritans and their descendants sure caused a lot of misery. Sadly, whatever gene causes zealous moralizing and a desire to punish heretics (modern day political correctness) stayed around too.

    • gcochran9 says:

      As for the idea that descendants of Puritans are a major force in current leftism: no. For example, old New Englanders account for about a sixth of the population of Massachusetts.

      • Jim says:

        Then the high test scores of the Massachusetts population are not primarily due to their genetic heritage from old New England?

        • gcochran9 says:

          Obviously not. 22.5% Irish, 13.5% Italian, Quebecois 8%. 9% black. 6% Asian. Hispanic/Latino 11%.

          English descent: 11.4% : only are a plurality in some towns in western Massachusetts. That number may be understated, and probably is, but not by a fantastic amount.

          • Jim says:

            Interesting. Generally on comparisons between US states on academic achievement Massachusetts is usually near the top. I wonder why that is so?

            • Pincher Martin says:

              Internal migration selected for the more talented in the country in order to fill up the jobs at all the many fine colleges and universities in the state, as well as the hi-tech companies those universities have helped spawn?

              As a small example of this, I see that the Bay State’s population has gone up nearly threefold in the last 110 years (1900-2010), but the number of Jews in the state went up more than thirteenfold in that same period, while the total American Jewish population increased only sevenfold.

          • dearieme says:

            “Obviously not. 22.5% Irish, 13.5% Italian, Quebecois 8%. 9% black. 6% Asian. Hispanic/Latino 11%.”

            I’ve often seen such figures from the US. I don’t see any reason to believe them. In fact, I don’t see what they are meant to mean. What the hell can 22.5% Irish mean? Does nearly a quarter of the population claim to have no non-Irish ancestors? Phooey!

            • Wency says:

              I think the stats usually come from a Census survey (not the actual Census) and are driven by self-identification.

              My guess is that this self-identification, once aggregated, still tells you a lot about the origins of the community, if only because it tends to be driven by surname. If your name is O’Malley, there’s a pretty good chance you’ll consider yourself Irish when pressed to identify your ancestry, even if you’re only 1/4 Irish. But so long as Irish weren’t dramatically more/less likely than Italians to abandon their surnames (e.g. by different marriage patterns), the surnames still carry information about the proportion of Irish to Italians.

              You could also use surname analysis, but this can be a problem. A branch of my extended family is German and Anglified its German surname during WW1, but they still know that they carry a German name and would identify their primary ancestry as German if pressed.

              Bottom-line: it’s flawed, but I suspect it’s still highly correlated with reality. This correlation almost certainly weakens with each generation though.

            • JayMan says:

              Self-identified ethnicity is fairly noisy in the U.S. census, especially for the Irish:

              Demography is Destiny, American Nations Edition

              The descendants of the Puritans are indeed a minority among modern-day New Englanders. Migration (and assortative migration) explains the political/IQ skew/

          • carol2000 says:

            “However, demographers regard this as a serious undercount, as the index of inconsistency is high, and many, if not most, people from English stock have a tendency (since the introduction of a new “American” category (See Old Stock Americans) in the 2000 census) to identify as simply Americans[6][7][8][9] or if of mixed European ancestry, identify with a more recent and differentiated ethnic group.[10]”

            • gcochran9 says:

              I know about that: but you don’t see a lot of that “american” category in Massachusetts.

              • carol2000 says:

                In 1980, the ranking was English > German > Irish. “However, … for 2008 we find something very surprising: The number of Americans claiming English heritage (9.0 percent of the total population) has fallen well behind those claiming to be German (16.5 percent) and Irish (11.9 percent).

                What is going on? Millions of English-descended people cannot have suddenly vanished. Nor have there been millions of German and Irish immigrants in the last 30 years. There are several possible explanations….”


              • gcochran9 says:

                I’ve written about it on this blog. I know quite a bit about it.. But even with the ‘flight from Englishness’, most people in Massachusetts aren’t old rock-ribbed Yankees. In part you can blame Tamboura.

      • jason says:

        20 million descendants of Puritans is about 6% of the current American population so that makes sense. But among the hard core White Leftists, I wonder if they aren’t still a big force.

        • gcochran9 says:

          Sure: just look at how Vermont and New Hampshire voted in 1936.

          Do I have to write that big post about how the Unitarians turned the Jews into Mensheviks?

      • Misdreavus says:

        That’s an dishonest trope invented by Mencius Moldbug, largely to draw attention away from the preeminent role of Jewish immigrants in American leftism. “Cathedral” my ass. More like “The Synagogue”, if you ask me.

        I can’t believe it even worked. The Talmud must be right, the goyim are cattle.

  5. luisman says:

    […]How much did this drop IQ?[…]
    How much more food would an IQ130 farmer produce vs. an IQ85 farmer? Probably not much.

    The survivability of kids depends mainly on the available food supply at any given smaller time span, if hygiene habits don’t change rapidly and absent of catastrophic events. The oversupply of food would be a basic condition for
    a) increased survival rate for kids
    b) leisure time in order to persue (pursue?) tasks that require a high IQ
    It’s increasing the chances to produce more high-IQ individuals, who have also the chance to produce some results which require a high IQ.

    At that point, what role plays natural selection (pure survival) vs. sexual selection (survival with max. comfort)?

    • pyrrhus says:

      An IQ130 farmer would produce vastly more food. Modern farming is complex and requires a lot of decision making and care. An IQ85 farmer would probably fail and go bankrupt within a few years…..

      • luisman says:

        This might be the case for large scale farming in the US, about which I don’t know any details. I lived in a farming area in the EU for many years, and the only complex issues there are the EU farming regulations. However, the local politicians resolve these complex issues with their high level attorneys and university institutes. The small/mid scale farmers just follow their advice, they need to know how to operate their vehicles, which buttons to push on their equipment, and follow the logistic processes which are standardized. Very few farmers operate outside of the regulations and usually make less money if they go green/eco and produce much less food. A tiny number establish a private, direct to the customer distribution system and earn more, but also produce less food.

        • Tom Bri says:

          I lived two years in a poor mountain village in Guatemala. I’d say intelligence plus determination made a huge difference among them. It was clear to see who was barely scratching enough to survive and who was trying to get ahead.
          And anyone who thinks even peasant farming is simple, simply has never tried it.

          • luisman says:

            If determination means high conscientiousness, I agree. Lazy, sloppy farmers are unlikely to succeed. But the individual intelligence of the farmer does IMO make no big difference. Those who follow the intergenerational accumulated knowlege about the local farming conditions will probably be better off than those who dont. Farming is simple – hard work but simple work. I tried it in my youth. Married a farmer’s (who had 8 kids) daughter.

  6. AppSocRes says:

    My 1968 undergrad course in physical anthropology was taught by a fanatical third-generation Boasian but still included materials authored by Mueller and Dobzhansky on the dangers of increased genetic loads in advanced societies as a result of reduced selection pressures. The topic seems gradually to have become toxic to mainstream careers. I can guess why. I’m glad that people like professor Cochran are still brave enough to raise the issue in a reasonable way.

    I suspect that the main thing driving increased genetic loads in advanced soicities is not differential morbidity and mortality but differential fertility. The more fit reproduce at a significantly lower rate than the less fit. And this does have readily observable consequences. There has been a secular decline in average response times – highly correlated with IQ – over the last century. A bigger question is whether these trends in decreasing average fitness will in the long term prove to be self-correcting and flatten out or reverse.

  7. J says:

    The puritan settlers have been in America for about 15 generations. If they had a higher IQ to begin with (which isn’t unreasonable to assume for settlers) a decline could leave them roughly the same as later European immigrants. Half-a-point a generation decline would take a 107 average to 100. I doubt it is as high as the 1 point a generation that Iceland has been experiencing, that would likely be an upper bound.

  8. Ryan Baldini says:

    How fast can this work?

    Under the implied model, Delta of breeding value = Delta due to mutation + Delta due to selection

    Let’s take a vague biological robustness, the kind that helps you not die as a kid, as our trait. I suppose we could actually define it as P(not die as a child), or some transformation of it to make it kind of linear (logit). Anyway, mutation is pushing in opposite direction to selection (on the whole), due to the fact that most mutations are deleterious to things are work properly. So Delta due to mutation is the upper bound on the change due to relaxed selection, achieved only if selection goes away entirely. In reality it will be less than this upper bound.

    How big can this term be? Mathematically it is sum_i mu_i alpha_i, the sum of the mutation rate of locus i (mut_i) times the effect of the mutation’s effect on the trait (alpha_i), summed across all loci i that effect the trait. I guess this suggests that traits affected by more loci ought to melt down faster – not unlike the total load calculation.

    Perhaps another approach: If the trait was in equilibrium prior to relaxation, then Delta due to mutation = Delta due to selection in magnitude, so the Delta due to selection prior to relaxation is also an upper bound on how fast the trait can degrade after relaxation. So we can ask: how strong was/is selection for e.g. childhood survival in a subsistence population at carrying capacity? I seem to recall some recent papers trying to quantify this using historical pedigrees, though some of those studies were actually for growing pops like Quebec.

  9. I mean…

    Take the extent to which children are dumber than their parents on average thanks to de novo mutation, and multiply by the number of generations after relaxed selection began. The difference must be so slight- I’d be surprised to learn that anyone had accurately nailed it down.

    Here’s a fun one: If mutational load destroyed our brains faster than it seems to, could we in our current state even be possible? Could mutation rate be a cosmic filter?

    • j says:

      Relaxed selection benefits not only de-novo mutations, but also existing ones.

      Quantitative expansion and quality degradation are not necessarily related. When the fitter are having more grandchildren, the population is ameliorating. Selection never stops.

  10. Jonathan says:

    There were population explosions in the 16th and 19th century for Ashkenazi Jewry, which does not appear to have affected their intelligence.

    Of course one could argue that having a high average intelligence helps reduce child mortality as members would tend to make fewer fataly bad decisions.

    • gcochran9 says:

      I don’think that the Ashkenazi Jews went through a long period of unusually low mortality. Not like people in Massachusetts or Quebec.

      By the way, if the Ashkenazim have longer lifespans because of lower-than-average genetic load, you would also expect them to have had lower infant mortality than other populations in a similar situation – not because they followed kosher.
      And that was the case.

  11. Harold says:

    Do embryos with higher load get rejected more?

  12. dave chamberlin says:

    As a long time reader of West Hunter I am guessing optimum brain function, as expressed by genius level IQ, is the result of mutational load never taking a big hit on any of a number of brain functions we still know very little about.

    The total mutational load of a genius may be almost identicle to that of an average person if this is the case. What makes me inclined to think Cochran is on to something regarding mutational load determining the wide variation in hiuman intelligence is it answers multiple questions. We are not evolving higher intelligence unless pushed incredibly hard (example, the Ashkenazim). We are ever so slowly losing intelligence when in periods of relaxed selection. The bell shaped curve of human intelligence points to a lucky few getting the right genes for high IQ but their children predictably regress to the average.

  13. says:

    Just a rough check. Most Australian are descendents of the British.

    From OECD,

    15 years later, the 2015 OECD PISA scores,

    Not sure about the long term effects. For the short term from avail data for 40 countries,

    PISA15 = -2.83*InfMort2000 +510.0; # n=40; Rsq=0.4779; p=7.873e-07

    For the short term, lower infmort -> higher PISA score -> better GDP -> better health -> lower infmort

    • says:

      With only 3 data points. Big drop in corresponding cohorts’ PISA3 for AUS. Mixed results for GBR.

      Year InfMort Pisa3 Country
      1994 5.9 518.84 # AUS
      1997 5.3 512.33 # AUS
      2000 5.2 502.33 # AUS

      1994 6.2 500.1 # GBR
      1997 5.8 502.33 # GBR
      2000 5.6 499.67 # GBR

  14. anon says:

    “We know that this relaxed selection among pioneer types left a higher burden of Mendelian disease – not incredibly high, but higher than in similar groups that didn’t undergo a rapid expansion.”

    I assume these Mendelian diseases are serious diseases and near absolutely fatal prior to one’s reproductive years (given pre 20th century medicine).

    Given that assumption, the only way I can see selection against them being relaxed is in the case where couples who are both heterozygous carriers take a few extra pregnancy at bats (after losing a few homozygous recessive children). And this happened at a greater rate than in more Malthusian societies.

    Yes/no? Any alternative mechanism?

    That’s a cruel paradox– abundance leading to reduced fitness. But I suppose it is indeed analogous to advanced healthcare over multiple generations.

    • gcochran9 says:

      Mendelian diseases are generally recessive: when the causative allele is rare, the full-blown disease is even rarer. But the typical recessive lethal has a small negative effect in heterozygotes, something like 2% I in fruit flies).So when the allele is rare, most of the purifying selection against it happens in heterozygotes. But if life is easy, less so.

  15. rob says:

    Autism seems mighty common these days.

  16. Tom Bri says:

    What percent of people have no children these days compared to earlier times? I would think for the lower IQ males reproduction is rare. Even if we believe the low IQ fraction is outbreeding the high IQ, is it the bottom end of the low IQ, or the top end?

    • Warren Notes says:

      Is there any evidence that reproduction is rare for lower IQ males? That seems counter-intuitive to me. Keep in mind that marriage is becoming increasingly rare for the lower class and even the middle class. The lack of a requirement to clear the marriage hurdle (along with a weakening of commitment to provide for offspring) presents opportunities for less committed serial relationships. Lower IQ should also be associated with less effective use of birth control.

      • Tom Bri says:

        It’s a question I have, and hope someone here might have an answer. My thinking is that even low IQ women try to get better class men, which might mean an IQ 90s guy, while avoiding obvious losers, however they consider that. It’s not a view I would strongly defend, just a suspicion. So IQ 80s women shooting for 90s men, with the poor 60s men not having much of a chance.

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