The long and short of it

A number of people have argued that there can’t be real evolutionary change in less than some huge amount of time – 50k years, 100k years, basically whatever number  they need to win an argument.  That’s all bullshit.  On the other hand, some people seem to think that you can get a lot of change in one generation without particularly trying.  That, too, is bullshit.

When someone suggests that evolutionary change is the reason that behavior X or trait Y has changed noticeably  (in a particular population) since the 1950s – they’re wrong.  Roland Fryer has argued that the rigors of the Middle Passage selected for salt sensitivity in African-Americans. But he’s for-sure wrong.  First,  there is no evidence that a higher-than-average tendency to hold on to salt would make much difference in someone’s chance of survival on a slave ship.  Lots of the mortality had nothing to do with salt retention: why would it protect you against smallpox or pneumonia? Second, even if there was,  it wouldn’t have a huge effect, partly because mortality on slave ships  wasn’t that high – around 15% in the 17th century, not that much higher than among immigrants from Europe in that period (~10%). If they lost the bottom 15% of the people (in ways related to salt retention) during the Middle Passage, a cutoff of about one std below average, the increase in salt retention would be about a tenth  of a standard deviation, assuming a narrow-sense heritability of 50%. You’d never notice the difference.

Along the same lines, Charles Murray, in an essay in Commentary, explains higher-than-average IQs among the Jewish people as a whole (not just among the Ashkenazim) as caused in part by the exile to Babylon.  Nebuchadnezzzar “carried into exile all Jerusalem: all the officers and fighting men, and all the craftsmen and artisans… only the poorest people of the land were left” (2 King 24:10).  Murray suggests that this group was an elite, and that later the Jews were largely descended from returned exiles.  First, non-Ashkenazi Jews do not even have higher-than-average IQs.  There is not much reason to think that they ever did. Certainly no one in Classical times ever had that impression.

Second, if you take along the army and all the potters and shoemakers, they’ll way outnumber anyone you could call an intellectual elite – it’s not a strong selective event..   Third, we have no reason to believe that most of the ancestry of the Jews in Israel in, say, Roman times was primarily from returned exiles.  It certainly can’t be true today: about half of Ashkenazi ancestry is actually European, probably Italian as much as anything else.  Sephardic Jews are also around half-European, although those were probably different Europeans.

In using an ancient and poorly-documented possibly-selective one-generation event as an explanation of a general phenomenon which does not even exist, Murray makes Fryer look like a genius. By comparison only, because Fryer’s argument has zero chance.

How much could IQ have changed, since the 1950s, due to selection? 2 points would be a stretch.  Now replacement of one population by another can happen in that time, certainly locally, and then you may be comparing populations that have been subject to different selective pressures for as much as a hundred thousand years.  They can be as different as all get out.  I know of actual live people who are convinced that the schools in Brooklyn have gone to hell, since the black and Hispanic kids of today seem to be doing so much worse academically than the Jewish kids of yesteryear. Really.  They think that.

Selection changing IQ at half a point a generation can happen – is happening –  and  can create big, interesting differences in a thousand years.  But we must remind everyone that 1000 is considerably bigger than 25:  it is right to worry about what happens if this goes on, but it is numerically incorrect to pretend that all that much has actually happened so far within populations, since the birth of effective  medicine, the welfare state, feminism, or whatever trend you’re worried about.

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70 Responses to The long and short of it

  1. The Man Who Was . . . says:

    Certainly no one in Classical times ever had that impression.

    Is this true? This guy says the opposite. (See p. 39. You can search inside.)

    No problem with the rest of your argument.

    • gcochran9 says:

      It is true. As far as I have been able to determine, there is not a single statement in preserved classical literature that says that the Jews were especially clever. Charles Murray suggested to me that Jews in Classical times had a rep as being greedy, crafty in their dealings: but I find no evidence for that either. The moneylender niche is being projected backwards in time. It is as if you talked about Arminius wearing a monocle and Pickelhaube.

      Murray mentioned Cicero saying something like this. I believe he was referring to ‘Pro Flaccus’, in which Cicero is busily slanging everybody his client stole from – pounding on the table mostly, since he was obviously guilty. He talks about the Jews and ‘their mania for gold’ – they didn’t like Flaccus stealing from them – but he talks far more about the Greeks. He says that they’re all liars – but first he says

      “But I say this of the whole race of Greeks; I allow them learning, I allow them a knowledge of many arts; I do not deny them wit in conversation, acuteness of talents, and fluency in speaking; even if they claim praise for other sorts of ability, I will not make any objection; but a scrupulous regard to truth in giving their evidence is not a virtue that that nation has ever cultivated; they are utterly ignorant what is the meaning of that quality, they know nothing of its authority or of its weight. ”

      Everybody thought the Greeks were smart back then: no one ever said it about the Jews.

      • The Man Who Was . . . says:

        Take a look at the citations in the book. As I said, you don’t even have to go to the library. It’s right there on p. 39 on Amazon.

      • L. Ron Man says:

        “Everybody thought the Greeks were smart back then: no one ever said it about the Jews.”

        So…what happened? Nobody particularly thinks this today. Was there a dysgenic process, or did northern Europeans just have greater innate potential, which was unleashed once they were civilized?

    • drphysics says:

      The reference (Origins of Anti-semitism) only asserts that Judaism was associated “…with the traditions of ancient philosophy” and that Jews are a philosophical people. It’s not clear to me that this necessarily means they are perceived as being smart. It is suggestive, but hardly the same level of endorsement given the Greeks by Cicero.

  2. albatross says:

    Is there any data about the selection effects of the holocaust? That seems like an example of an event with enough impact to change the genes of the survivors in just a few years, since some big fraction of the Ashkenazi Jews in the world were murdered in a few years. It seems like some heritable traits (willingness to flee far from your home? Sufficient paranoia to GTFO while the Nazis were letting Jews out?) should be associated with survival. But I’m not sure how much was just geography–lots of the holocaust’s victims (I think the great majority) weren’t German, and may not have realized that the rise of Hitler meant they needed to flee Poland. That’s also linked to some genetics, obviously.

    What other events are big enough to have a one-generation effect? Maybe WW1, the US civil war, or some of the big plagues? I’m not sure what the selection effect of the wars would be, but they seem large enough in impact to actually have a one-generation effect. I wonder what effect, if any, HIV is having on sub-Saharan African genetics.

    • gcochran9 says:

      The Black Death, maybe. But then it showed up again and again. If you think that something like the Civil War had a noticeable selective impact, you have a seriously wrong idea of how such things work.

      • RS-prime says:

        Check the casualty rates for Dixie /head vs those for the war at large.

        • gcochran9 says:

          I know them. But I also know and understand the breeder’s equation. Look, losing 5% of the population is never going to have much of a selective effect. First, it is not as if those Southerners who fought for the Lost Cause were wildly different from those managed to avoid doing so. The South didn’t pick soldiers by high IQ, or low IQ, or salt retention, or anything else in particular. Second, 5% is only 5%.

          You could certainly argue that the institution of interstate warfare, over centuries or millennia, may select for people who at minimum don’t volunteer But single-generation effects are usually pretty small, unless you do something like shoot the bottom 85% of IQ. That would increase average IQ by about 11 points, assuming 0.5 narrow-sense heritability.

  3. Der Alte says:

    Click to access 20061129_MurrayPowerpoint.pdf

    The link is to Charles Murray’s Powerpoint for his debate with Flynn on black IQ.
    Below is one of the last slides.
    How much would this “dysgenic pattern of fertility among black women” decrease IQ per generation? More than half a point, I would think.

    The dysgenic pattern of fertility
    among black women.
    􀂄 The NLSY-79 women (born 1957–1964)
    have completed their fertility.
    􀂄 58 percent of black children were born to
    women with IQs below the black mean.
    􀂄 50 percent of white children were born to
    women with IQs below the white mean.

  4. gcochran9 says:

    Knowing that 58% of black children were born to women with IQs below the black mean doesn’t tell you enough. You need to know the average IQ of the parents. That stat doesn’t tell you. It doesn’t even tell you the average IQ of the mothers. What if all of the extra below the mean was in a bump 1 pt below the mean? In that case the impact would be tiny. The extra reproduction among women with below-mean IQs would have to be found in women who averaged about 6 points lower than the mean in order to decrease IQ by half a point per generation, assuming a similar distribution among the fathers and a narrow-sense heritability of 50%. Unlikely. And even then, you couldn’t notice a half-point population difference if you tried.

    • Der Alte says:

      “Knowing that 58% of black children were born to women with IQs below the black mean doesn’t tell you enough. You need to know the average IQ of the parents. That stat doesn’t tell you. It doesn’t even tell you the average IQ of the mothers.”

      I think it’s possible to make an educated guess as to the mean maternal IQ of black babies.

      “What if all of the extra below the mean was in a bump 1 pt below the mean?”

      Kind of unlikely, don’t you think?

      • Der Alte says:

        Assume that maternal IQ of black babies is normally distributed. Then the 58% figure would put the mean 0.2 SDs below the mean for black women. Low-balling the SD of maternal IQ of black babies at 10 would put mean maternal IQ of black babies at 2 points below the mean for black women.

        Maybe black daddies are smarter, on average, than black men. But, “assuming a similar distribution among the fathers and a narrow-sense heritability of 50%”, wouldn’t you have a 1 point drop per generation?

        • gcochran9 says:

          Right. But if Murray had bothered to mention the average, that exotic quantity, we wouldn’t have to guess. It would be nice if he, and everyone else in the public arena, bothered to read the wiki page on the breeder’s equation, but I guess that’s just too damn much to ask.

      • JayMan says:

        Here are some data on the matter:

        Dysgenic Fertility Among Blacks? Apparently, Yes « JayMan’s Blog

        I’m doing a more comprehensive look going back further in time. So far, I’ve found that the pattern is very similar, only that the average number of children is considerably higher across the board for the older generations.

  5. jb says:

    Here is what may be is a different question: supposed that in a certain generation nobody with an IQ above 130 reproduced at all. How much would that affect the number of people in the next generation with an IQ above 130 (by which I mean 130 as normed to the previous generation)? How about the percentage with an IQ above 145?

    What I’m interested in of course is the effect of dysgenic breeding, not on average IQ, but on the number of exceptionally intelligent people in a population. Is this in fact a different question, and does the breeder’s equation give you any answers?

    • gcochran says:

      Shooting everyone with an IQ above 130 would decrease the mean by about a point. It wouldn’t make a huge difference.

      The change in the mean is the story, really, at least if we’re talking about a homogenous population.

      • jb says:

        I guess what I was asking is whether it would distort the shape of the bell curve, at least temporarily, by suppressing the right hand tail. If the mean shifts slightly, would that be due to the curve as a whole moving a little to the left, or would the shift be due to the far right of the curve having been flattened (which would mean you no longer have a true bell curve)?

        To put it another way, I’m wondering about the effect on the size of the smart fraction in the next generation. The thing is, I know a lot of smart people who have few or no children, and I lament the children they aren’t having. If it’s true in general that highly intelligent people are having fewer children than the average or stupid, then it seems to me that the next generation will suffer a shortfall of people at the upper end of the spectrum, even if the average doesn’t budge much. The loss of a good sized chunk of the relatively small smart fraction strikes me as something that would have a bigger impact on society than a minor shift in average intelligence.

      • jb says:

        Sorry to poke at you again, but I’m really curious about this. At least intuitively, it does seem to me that shooting everyone with an IQ over 130 would in fact distort the shape of the bell curve, at least for a generation or two, and that this distortion, by reducing the size of the “smart fraction,” would have a much bigger impact on society than the relatively small associated shift in average IQ. Wouldn’t subtracting a small right shifted bell curve (the children of the high IQ people) from a larger bell curve (all children) have to leave you with something asymmetrical?

  6. Insightful says:

    This is from Henry Louis Gates:

    How many African Slaves Landed in the US?

    Between 1525 and 1866, in the entire history of the slave trade to the New World, according to the Trans-Atlantic Slave Trade Database, 12.5 million Africans were shipped to the New World. 10.7 million survived the dreaded Middle Passage, disembarking in North America, the Caribbean and South America.
    And how many of these 10.7 million Africans were shipped directly to North America? Only about 388,000. That’s right: a tiny percentage.

    In fact, the overwhelming percentage of the African slaves were shipped directly to the Caribbean and South America; Brazil received 4.86 million Africans alone! Some scholars estimate that another 60,000 to 70,000 Africans ended up in the United States after touching down in the Caribbean first, so that would bring the total to approximately 450,000 Africans who arrived in the United States over the course of the slave trade.

    Incredibly, most of the 42 million members of the African-American community descend from this tiny group of less than half a million Africans.

    • gcochran says:

      They increased by a factor of 80: the French Canadians increased by a factor of 1000. Geometric growth is only amazing if you don’t understand it.

      You don’t often see rapidly expanding slave populations in history. It requires an extremely non-Malthusian situation.

      • M. M. says:

        re. They increased by a factor of 80: the French Canadians increased by a factor of 1000.

        Are there estimates of birthrates for blacks and whites in that era? Why were black birthrates lower exactly? Malnutrition, working conditions? Were they prevented to procreate by force in relevant numbers?

        • gcochran9 says:

          Slaves had pretty high rates of population growth in the US, just not as wildly high as the French Canadians. Blacks were 19% of the US population in 1790, 14% in 1860, but there was lots of white immigration over that period, while importing slaves was illegal after 1808. It’s probably better to look at the South, which had less white immigration. Slaves were about a third of the population of the South in 1790 and about a third in 1860 – growth rates must have been about the same.

  7. ben g says:

    What makes you confident that IQ tests map on to the conventional understanding of “intelligence” in ancient times?

    We have relatively reliable/stable correlations between different cognitive tests (g) and g is correlated with real world outcomes in the 20th/21st century. How does the current evidence from psychology allow you as a scientist to assume that IQ == a timeless definition of intelligence?

    • gcochran9 says:

      Today, IQ measurements are decent predictors of the ability to solve complex problems. People who were good at such things in Classical times were usually considered intelligent: it seems to me that people who were considered intelligent back then, people like Eratosthenes or Archimedes or Hannibal, would seem so today.

      I suspect that natural selection has made some changes in the human psyche since those days, but not so much as to make those oldsters utterly alien to us today.

      You know, your comment was really stupid.

      • ben g says:

        IQ tests are built/judged around their reliability and validity in predicting educational/economic success in the modern first world, not in matching some timeless definition of intelligence.

        Would the complex thinking required by IQ tests overlap with what people saw as intelligent in different times and places? Surely, but to what degree?

        It seems like you’re going more based on hunches than on any sort of data on this one.

      • asdf says:

        I’m with ben g. The kind of abstract thinking skills that allow one to do nuclear physics and the kind that allow one to build an aqueduct aren’t the same. The middle east once had a golden age of relative advancement for its time, yet nobody today implies this is a sign that those people had high IQ the whole time.

  8. alvarez80 says:

    IQ tests are built/judged around their reliability and validity in predicting educational/economic success in the modern first world

    IQ tests are “built” to test one’s abilities at pattern recognition and abstract reasoning . . . abilities which, for most of any population, affect levels of “success” in the first world, the second world, the third world, the ancient world, or any other world you’d care to mention.

  9. dave chamberlin says:

    Either you can argue that you can’t have real evolutionary change in 100 years or that we are decreasing our average IQ 2 points per generation, you can’t argue both because one contradicts the other. An actual across the board decrease in IQ of 7 or so points (100 years of 2 points per generation decline) for a modern nation such as the United States would be crippling. Fortunately the five children of Greg Cochran are going to out into the world and find mates of near equal intelligence. We aren’t losing our intellectual elite, matter of fact we are recruiting the best and the brightest from the rest of the world and they are more than happy to take up our invitation. So while average IQ may decline, we will still have a sufficient percentage of the population out there on the long left tail of the bell shaped curve of human intelligence. There are places in the world wherer the average IQ is seven points less than the US and they are rapidly sinking into the worst case scenario of the malthusian trap. It is not politically correct to talk about but that doesn’t make it any less true.

    • gcochran says:

      Optimism based on the idea of increasing assortative mating is unjustified. Which means that you’re wrong, which is too bad.

      • dave chamberlin says:

        You probably know better than I do. I would like to say we shall see but we won’t, we will both be dead before the results are in, but thanks for answering. To anonymous below my argument about assortive mating has nothing to do with statistics. It is a simple statement of that college board exams which use a form of intelligence tests to allow men and women into the best colleges has radically changed how often very bright men choose very bright women for mates. Lots of assumptions on my part which Cochran disagrees with, but still, it is a radical change from earlier arrangements of how people were paired.

    • Anonymous says:

      I think that your optimism about assortative mating is wrong. Here is a simple example.

      Take a population with IQ normally distributed (100,15) that follows classical quantitative genetic assumptions and a heritability of 1. Split them in two, those above the mean and those below the mean, and keep all marriages within group. After the split the mean IQ in the two populations is 92 and 108 (approximate but good enought), and the within group variance is 81 so the within group standard deviation is 9.

      In the original population 2.2 % had IQs over 130, two SDs above the mean, from a table of the Normal distribution. After the split and imposed assortative mating the number of people with IQs over 130 is the number of people in the high IQ group more than 22/9 or 2.4 standard deviations above the high IQ group mean of 108. This is 1% of the high IQ group or 0.5% of the total population. Our genetic meritocracy has reduced the number of high IQ people to slightly less than 25% or its initial value.

      Take the mating system all the way to fixation, so that there is no within group variance and all the variance is between groups. In this limit the two groups have fixed IQs at 85 and 115 and no one has an IQ over 130!

      I have to admit that the above contradicts my intuition: probably some mistake in it and someone here will point it out.

      • anon says:

        “After the split the mean IQ in the two populations is 92 and 108 (approximate but good enought), and the within group variance is 81 so the within group standard deviation is 9.”

        Based on Monte Carlo simulation (don’t know or care to learn about the maths) and looking only at the higher group for simplicity’s sake: the initial generation’s phenotype is 112 w/ a sigma of 9. But this cohort is simply half a bell curve–the normal distribution table is inapplicable. They also haven’t undergone mean reversion–the expressed phenotype is not representative of the underlying genotype. The offspring from this group is normally distributed (~106,~14.2).

      • RCB says:

        This is old, but I think I found the errors to Henry’s calculations.

        First, the post-split mean of the higher group is about 112, not 108. So that’s big.

        Second: Henry is correct that the post-selection but pre-reproductive variance of each sub-group is 81. But, upon reproduction, much genetic variance will be recovered due to genetic segregation within families. If this is unclear, consider: even if we kill off everyone but one couple of the same phenotype (thus 0 variance), segregation among many different heterozygous loci within parents during meiosis will ensure that their kids will differ – even with heritability 1, as Henry assumed (this, incidentally, is why anon’s comment about reversion to the mean is incorrect).

        So what is the correct answer? I wager that the total variance after reproduction will be the variance between families (81/2, assuming random mating within the new high group) plus the variance due to segregation within families, which depends on the amount of assortative mating that existed prior to the split. If folks mated randomly before, then half of the previous additive variance will be within families (a classic quant gen result). So the total variance should be something like (1/2)9^2+ (1/2)15^2 = 153. So the new SD is about 12.4. Once normality is recovered (in a few generations?), this means that the proportion above 130 will be about 0.07. A big increase over 0.02.

        If folks didn’t mate randomly before the split (and they probably didn’t), the variance recovered by segregation will be less (higher homozygosity across the genome), so the proportion above 130 will be lower. I think under perfect heritability the segregation variance is something like 1/2V_A(1-r) at equilibrium, where r is the correlation between mates. Let’s say r is about 0.5, so the segregation variance is reduced by half. Then the total variance will be (1/2)9^2 + (1/4)15^2 = 96.75, leading to a SD of 9.8. Then the proportion above 130 is about 0.03 – only a small increase.

        All of this is likely to change under imperfect heritability, which is the case for IQ.

        It’s quite possible that the exact numbers are off, but the basic ideas are right, I believe.

        • RCB says:

          Actually, I have made one important error: If random mating continues, I think the segregation variance continues to be 15^2, meaning that the population will geometrically recover the variance of the original population. So, with mean 112, and SD 15, the proportion above 130 will approach a whopping 0.115.

          The relevant theory can be found in Bulmer’s classic quant gen book. Positive selection on a quantitative character with infinite number of additive loci ends to reduce selection only during selected generations. After selection ceases, the population eventually recovers all additive genetic variance.

          In reality, there aren’t an infinite number of loci or people, so some genetic variation will be lost.

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  11. JS says:

    “On the other hand, some people seem to think that you can get a lot of change in one generation without particularly trying. That, too, is bullshit.”
    If the left hand side of the bell curve intermarry and have 3 children each, and the right hand side of the bell curve intermarry and have one child each, wouldn’t the shape of the curve change dramatically in just one generation?

  12. hbd chick says:

    @greg – “It would be nice if he, and everyone else in the public arena, bothered to read the wiki page on the breeder’s equation, but I guess that’s just too damn much to ask.”

    there isn’t one. =(

    but here’s maybe a good place to start?

  13. Noxi says:

    Arabs persians turks have competitive civilisations for long periods of time. Why do they score less in modern iq tests

  14. statsquatch says:

    They need to look the wiki page on the truncated

  15. dearieme says:

    Probably true for Arabs too. But the Persians supported high civilisations for ages so Noxi still needs an answer.

    • Bob Arctor says:

      That’s certainly true for Arabs, though it’s obviously not true for Semites more generally. Persians are an interesting case, and I don’t have an answer for what happened there.

  16. There is some evidence that the Jews were especially talented in ancient times. You will find it in the best parts of the Bible. The best parts, mind, not the worst. If we judge by the worst no people comes out looking good.

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  19. tommy says:

    I think the answer is what seems obvious in this case: the Ashkenazim tend to be concentrated in communications-related professions to this day and they show a large gap between verbal and visuospatial IQ. This is about what I’d expect of an ethnic group that carved out a niche for itself as a middle man minority whose principal skills were likely promotion, persuasion and argument. I might be entirely wrong, but I never got the impression from my reading that the Sephardim were really as highly constrained in their entrepreneurial endeavors as the Ashkenazim

    It isn’t hard to imagine a rather rapid increase in IQ if there were was a substantial difference between the smartest and dumbest members of Ashkenazi society whereby the dumbest were failing to even replace themselves at a time when the smartest could afford large families.

    That learned (at least in their own arcana) and argumentative rabbinical culture might have been a co-factor, helpful and possibly necessary, but not sufficient obviously. It probably didn’t hurt that the Jewish community was willing to expend resources to prop up promising students and this might ultimately have come at the expense of needier members of their own community.

    I think Murray and some others are taken in by references to large numbers of Sephardic thinkers during the Middle Ages. Some ridiculous percentage of medieval geometers were Sephardim, for example, but, as far as I can tell, they advanced geometry very little. It appears their status as geometers frequently rests on things like writing commentaries on Euclid much as they wrote ones on the Talmud and other rabbinical writings. It’s not all that impressive for a population that was exceptionally literate and financially comfortable for its time. I entertain the idea sometimes that the original Sephardic Jews in Iberia might have been some smart cookies given their economic prominence but most of the Sephardim who didn’t dissolve into the Iberian population dispersed among the less impressive Mizrachi and other Mediterranean and Near Eastern communities so it’s hard to tell nowadays. A closer examination of the fate and fortunes of the British Sephardim might be telling.

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  21. swply says:

    @ tommy,

    How much did European gentile mathematicians advance geometry or any branch of mathematics during the Middle Ages? There are a few greats from that period (e.g. Fibonacci), but not all that many. And if they weren’t disproportionately Jewish, they weren’t disproportionately northern European either.

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  30. Gongora says:

    In the Spanish Empire Sephardic Jews and conversos were overrepresented in the elite. Why then and not today?

  31. dlr says:

    I agree with you mostly, but what about for cases of very strong selection? Ever since birth control pills became commonly used (since the 70s) millions, maybe hundreds of millions, of people are simply removing themselves from the gene pool. This is putting up really strong selective pressure on a trait that isn’t evenly distributed in the population : the desire to have children . Prior to that time, all evolution had to do was make people want to have sex, and have a strong desire to take care of their children once they arrive. That’s not enough anymore, the desire to have children has to predate even conception. This is a trait directly involved in reproduction, unevenly distributed, and under strong selective pressure : people without it maybe have no kids at all, or, at most, one, people with a moderate level of the trait have a couple of kids, people with a high level of the trait, maybe have 3 or 4 … and use of birth control has become extremely wide spread in our society over the last 50 years — almost ubiquitous, certainly readily available to anyone who wants it.

    As far as I know, no one is measuring the trait in question, call it ‘philopropinquity’ but if it does exist, and is heritable, it has to be increasing in the gene pool at a dramatic rate.

    • Petja Ylitalo says:

      Not only desire to have children, also other similarly working things like females non-compatibility with hormonal contraception, or men who dislike condoms.

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