It has long been known that inbreeding is bad for you. A new paper in Nature (Directional dominance on stature and cognition in diverse human populations) finally gives us a good quantitative estimate of just how bad it is. They find that the offspring of first cousins suffer an average reduction of  1.2 cm in height and 0.3 sd in g ( ~4.5 IQ points) .  They directly measured runs of homozygosity –  more accurate than estimating from genealogy, and better in other ways as well.  Children of first cousin marriages also suffer an elevated incidence of significant genetic disease, roughly 1.5-2 times the non-inbred risk.

That’s not all that far from my previous horseback guess.  The field was full of old and messy studies, so horseback guesses were the best you could do, until now.

The article mentions that Darwin recognized negative effects of inbreeding (a bit too late): they also say that he was among the first to do so, which is not true.  Al-Jahiz talked about it back in the Abbasid caliphate (around 800 AD) and assumed that everybody knew about it: “as the reader knows, the same is the case with horses, camels, asses and pigeons when they are inbred. ”  I suspect that people noticed this soon after farm animals were domesticated, thousands of years ago.

In some parts of the world, mainly the Middle East and North Africa, cousin marriage is very common, with tens of percent of the population practicing it.  Repeated marriages among close relatives can sometimes push the homozygosity up considerably higher than the first-cousin level, with even worse results.

Some retards (British papers) have been spinning this as saying that there are big benefits to mixed-race marriage.   Untrue: to avoid lots of ROH (runs of homozygosity), just marry someone who isn’t from the same isolated population as you. We’re talking outside the valley or across the river : intercontinental travel is not necessary.  Now there might be a degree of hybrid vigor in some distant crosses (currently unclear) – but likely not enough to compensate for someone coming from a group that has low trait values. Marry a Pygmy and your kids are going to be short.  Marry someone from a population whose average IQ  is below 90 (much of the world) and your kids will on average be less smart.

Naturally, enlightened opinion increasingly supports legalization of first-cousin marriage, due to its usual ignorance, perversity, and nihilism.

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122 Responses to Inbreeding

  1. It is very good to see the Nature paper giving much better estimates of the inbreeding effect, and the whole field coming to the same, measured, conclusions.The 4.5 IQ points for first cousins is interesting, and shows how lots of ROH could explain very severe drops in intelligence with repeated cousin marriage, which even a few months ago seemed to be too big an effect to be credible.
    Everything seems to be coming together. Once again the question arises, what made researchers take so long to recognize the deleterious effects of inbreeding that were well known to farmers (apart from these researchers not being farmers)?

    • Paul Conroy says:


      Correct. I grew up on a farm and got a gift of a few Bantams when I was 8 yo. I collected the eggs initially, but then let a few bantams brood over their eggs, and so reared a few clutch of chickens. Then these clutches proceeded to interbreed. After 2 generations, I began to see that multiple chickens had strangely twisted claws, and one cockrell had a hump on its neck…

    • athEIst says:

      I think it was noted in the Spanish Hapsburgs. Isabella’s daughter Joanna the mad and the unstable Philip I of Swabia after 5 generations including 2 uncle/niece marriages and 2 first cousin marriages produced Charles II who left no descendents (and could not even eat due to the freakishly extended Hapsburg jaw).

  2. j says:

    Could you do a horseback (or camelback) guess the IQ depression in Pharaonic dynasties with brother+sister unions several generations in sequence ? Cleopatra’s brother was a total retard but she looks normal.

    • MawBTS says:

      Here’s a visualization of Cleopatra’s ancestry if it helps anyone.

      Looks like some weird bonsai sculpting happened to this family tree.

      • jamesd127 says:

        Cleopatra VII was famously smart, beautiful and remained youthful looking for longer than most women. I am therefore inclined to suspect that Cleopatra V got up to mischief, or was perhaps too retarded to tell who was her husband and who was not.

        On checking your proposed family tree, I find that violence and the struggle for power makes the ancestry of Cleopatra VII uncertain. Pretty much everyone in her family tree came to a violent end, thus probably some people had less royal blood than claimed.. In fact probably pretty much everyone had less royal blood than claimed. Although everyone claimed to rule though divine right and royal ancestry, they actually ruled through will and steel. It is more likely that Cleopatra comes from a long line of people skilled in plotting, assassination, seduction, treachery, and war, than a long line of inbred marriages.

        • MawBTS says:

          I didn’t make that image, its accuracy is probably more than dubious. I wasn’t aware that Cleopatra was regarded as a great beauty – didn’t Plutarch say she was sort of plain, but made up for it with her wit and charm?

          Then again, everyone knows you tell smart women they’re attractive and attractive women they’re smart. Maybe Plutarch was the Heartiste of the ancient world.

    • jasonbayz says:

      You can calculate that with the coefficient of inbreeding. For generations of repeated brother sister inbreeding it would be this(if I did the math right):

      1: 2(1/2)^3=.25
      2: 2
      (1/2)^3(1+.25) + 4(1/2)^5 = 0.4375
      3: 2
      (1/2)^3(1+.4375) + 4(1/2)^5(1+.25)+8(1/2)^7=.578125
      4: 2(1/2)^3(1+.578125) + 4(1/2)^5(1+.4375)+8(1/2)^7(1+.25)+16(1/2)^9=.68359375

      This can be compared to the coefficient for the children of a cousin marriage: .0625. So if the relationship between the coefficient of inbreeding and the IQ drop were a linear one you would would have an 18 point drop in the first generation of inbreeding and a 49 point drop by the fourth generation. However “natural selection” would remove the worst recessive genes as the generations went on.

      They do this in rats to get an “inbred strain.” By 20 generations of brother sister breeding you have a population that is 99 percent genetically identical. If you had enough time you could theoretically do this with humans. Imagine a royal family of people who all looked the same and acted and thought very similarly, created through inbreeding. But it would take quite a long time to do, I would think it would take longer than with rats as we have more dangerous recessive mutations that would have to be purged through selection.

      • Ilya says:

        @jasonbayz: wow! Coincidentally, I was posting about this very same idea on a different blog, led by James D., a couple of weeks or so ago. The thing is, inbreeding depression can be overcome with a high (very high!) fertility rate and sticking to discipline of a strict selection criteria (which includes health+IQ).

        Our esteemed host, Dr. Cochran, is absolutely correct in saying that sibling/first-cousin inbreeding, if practiced consistently and on a mass scale, is bad for the population that practices it, as families that practice it, have fertility that isn’t sufficient to overcome inbreeding depression associated with mutational load going homozygous. This effectively, leads to slow-but-sure accumulation of mutational load, in Muller-ratchet-like manner.

        However, an elite population pump consisting of a royal family that practices brother-sister pairing and super-high birthrate (potentially, recruiting women from general population as surrogate mothers for the royal pair’s zygotes) is exactly what’s needed to achieve a very quality family and, eventually, population.

        Helen Dean King did exactly this with her famous inbred rats, which is described in her “Studies on Inbreeding” (free to read):

        H.D. King achieved most recovery from inbreeding depression and stability with her rat deme around 7th generation, and good results by 16th. If we are smart about doing such breeding vis-à-vis a “royal” line (obviously, practicing primogeniture is out of question!), given the fact that most genes

        Inbreeding by royals/elite + very high fertility is a good practical way to cleanse mutational load, achieving what Dr. Cochran himself described here:

        The approach you & I are proposing is, basically, a type of selection. Except that when we achieve a 99.99…% homozygosity rate for an individual with good health and high-IQ, we, as imperfect species, can basically say that we arrived at a biological uber-mesch. (Obviously, culture will still matter a huge lot, even with “perfect” individuals like that!)

        • Ilya says:

          Need to finish the sentence:

          If we are smart about doing such breeding vis-à-vis a “royal” line (obviously, practicing primogeniture is out of question!), we can halve the typical generation time from typical 30 years to around 15 years (if we use surrogate mothers and create royal siblings’ zygotes in vitro). Given that most human genes (>80%, according to Allen Institute for Brain Science) are expressed in the brain, and pessimizing her figure from 16 to 20 generations, we will need 20*15=300 years to create an “uber-mensch” royal.

          Given that in the current United States of America people think at most in 1 generation timescales, if that!, this will only happen in either Israel or China.

          Happy Independence Day, ya’ll, by the way 😉

        • ursiform says:

          And then the right pathogen comes along …

          • Ilya says:

            @ursiform: Ha! By that time (200+ years), assuming this indeed happens, technology will enable to either:
            1) perform gene drives to disable the spreaders (google CRISPR + mosquito).
            2) reverse engineer the parasite to develop a vaccine.
            3) perform selective CRISPR fixing actual gene targets for the parasites.
            4) etc!

            I ask anyone to come up with any realistic scenario where true heterozygote advantage comes from things that are not legacy adaptations from times immemorial, where lived in low-to-no-tech world full of deadly disease! (Btw, just to preempt, I don’t count recovering from a fixated deleterious mutation as a “true” heterzygote advantage)

            Hopefully, in not too far future (within this century), heterozygosity should be abolished as a relic of archaic past, and we, as species, need to move into the post-industrial era, where all good traits are stably fixated, and bad traits weeded out.

          • melendwyr says:

            I’m afraid determining which traits are truly worth weeding out isn’t nearly as trivial as you imply.

          • Ilya says:

            @melendwyr: Hence the sibling inbreeding scheme w maximized progeny production, a la H.D. King and her Wistar Inst. rats.

            Once you start mapping which traits are possibly deleterious/beneficial via weeding out defective progeny, you get better and better confidence in your data as the genotype becomes more homozygous and the (good) phenotype more stabilized.

            Eventually, after 20 or so gens, you form a 99.99+% confidence about your very special clan. Thereafter, you can go wild, by, one one hand, preventing uncontrolled de novo mutations from ever materializing in your progeny’s gene and, on the other hand, introduce your own, custom mutations (be they your own or borrowed from other species), to run special experiments on genotype-phenotype correspondence and new trait development.

            This is a geneticist’s dream come true, my friend ;-).

          • Ilya says:

            And going back to ursiform’s comment about “then the right pathogen comes along…”:

            Worrying about that, assuming a very advanced-tech based civilization, is the same as modern Europeans living in Papua needing to worry about Papua cannibals by considering whether or not to live in protected in enclosures.

            Small thinking (so common today)!

      • RCB says:

        So I set up a system of repeated brother-sister mating equations and got a different result. The first four inbreeding coefficients are: 1/4, 3/8, 1/2, 19/32. It doesn’t seem right (not pretty numbers), but it is: Crow and Kimura’s pop gen textbook shows the same thing. Note these numbers are not as large as yours: we’d see a drop of 42.75 IQ by the fourth generation, instead of 49.

        A neat result is that, asymptotically, heterozygosity is reduced by about 19% in each successive generation. Already a good approximation by the fourth generation.

  3. Mindfuldrone says:

    You forgot to mention “fear of being branded Islamophobic”. First cousin marriages are a big problem in some Islamic societies

  4. Staffan says:

    I imagine hybrid vigor would be strong for Arabs having inbred severly for a long time, purging harmful alleles. It will be interesting to see if for instance immigrant groups might benefit from this, or if they will persist inbreeding in the West.

  5. dearieme says:

    I made acquaintance a few years ago with a woman who had been teaching in a “special needs” school in London, in which she dealt with terribly damaged wee mites, many of them the result of inbreeding. She resigned, in despair at the Pakistani population in particular failing to absorb and act on the damage that inbreeding does.

    I suspect that the detail of the immigration laws amplifies the attraction of inbreeding marriages.

  6. Rick says:

    “They find that the offspring of first cousins suffer an average reduction of 1.2 cm in height and 0.3 sd in g ( ~4.5 IQ points).”

    So, as long as it’s legal to marry a stranger who is 30 cm shorter than you, and 30 IQ points dumber than you, and with a known family history of genetic disease, then why not your cousin?

    It’s not like cousin marriages increase the frequency of low quality alleles in the gene pool. They just shuffle them around and might even purge a few terrible alleles.

    I don’t really see the problem.

    • Fourth doorman of the apocalypse says:

      It’s not like cousin marriages increase the frequency of low quality alleles in the gene pool. They just shuffle them around and might even purge a few terrible alleles.

      Well, there is a cost to having more dumb people in the community. However, it might not outweigh the cost of all those exotic-disease-bearing low-iQ illegal immigrants where a good proportion of the males appear to be rapists as well.

    • RCB says:

      Suppose we forced smart people to marry dumb people. Mean IQ would not drop.

      Now, to be fair, the proportion of the population that could learn calculus would drop, as it takes above-average intelligence to learn calculus (that may sound funny to college-educated STEMers like yourselves, but its true), and outbreeding would reduce variance. So we’d have less capable engineers, for example. But we’d also have less extreme idiots draining public resources, so some good would balance the bad.

      Same goes for any quantitative trait: mean won’t change from negative assortment. (I’m assuming mostly additive effects.)

      Now suppose that we made everyone marry a second-cousin. Suddenly many rare deleterious recessive traits would show up. Mean IQ would drop, without question. (Yes, these alleles would eventually be purged, on a generational timescale.)

      So, at least on a population level, there is a qualitative difference between large scale breeding of this type.

      • jamesd127 says:

        Experiments on guinea pigs and rats suggests it takes many generations before the permanent beneficial effects of the elimination of harmful genes outweigh the temporary harmful effects of inbreeding.

  7. jb says:

    First cousin marriage is in fact currently legal in many American states. This isn’t new either; two of my great-grandparents had a first cousin marriage.

  8. dave chamberlin says:

    This is a very important paper that needs to be heavily circulated in those parts of the world where cousin marriage is still common. For those like the above poster Rick who do not see any problem with lower IQ’s I wish they would read this paper

    Average lower IQ’s = increased human misery. It is a tough world out there and nobody but nobody should be voluntarily choosing that their children should take a 4.5 point hit on their IQ.

    In addition this paper lends validity to a hypothesis advanced by Cochran that common cousin marriage was an important factor in the Muslim world’s decline since their golden age.

    • Rick says:

      This just shows correlations, not causation.

      There is just no way that even frequent cousin marriage could be keeping any countries down. Anytime the chain is broken, the effects are lost. There are no runs of homozygosity in two unrelated people who’s parents were even siblings.

      • gcochran9 says:

        Sure it could, if a big fraction of the population was marrying first cousins. As for your second sentence (two unrelated people who’s parents were even siblings) I have no idea what you’re trying to say. Explain?

        • Peter Lund says:

          Two pairs of otherwise unrelated siblings have a child each. Those two children then have children themselves. Took me a while to parse.

      • I am not debating with you Rick that the negative effects of inbreeding can be easily removed by outbreeding, you are right. But the rate of cousin marriage in parts of the muslim world are staggeringly high. This source states that a whopping 70% of marriages in Pakistan are between first cousins. I don’t know how accurate that number is, it sounds astoundingly high, but it illustrates that first cousin marriage rates are indeed high enough in parts of the world to be keeping countries down. Family trees can become gnarled shrubs as this song suggests.

        • jamesd127 says:

          In the you tube video, the relationships are step, and inlaw not blood, hence though forbidden by the old testament, do not in fact produce inbreeding – though could well produce the family tensions the singer complains about. Current law, and to a lesser extent current custom, usually only forbids biological inbreeding, relations with actual kin, not step kin and in laws.

          • The 2nd link given is just funny/goofy with no real point besides that. The 1st link explains an extremely common form of marriage in the muslim world is a marriage between uncle and niece, typically a man marrying his brother’s daughter. Not only is this as bad as a first cousin marriage, but the negative genetic consequences are worsened yet further by an elderly man begetting children. Inbreeding has negative genetic consequences for one generation but a culture which encourages elderly men to become fathers accumulates increased mutational load for as long as it exists. There is a potential triple whammy going on in the Muslim world since it’s golden age. We have 1) inbreeding 2) increased mutational load and 3) influx of sub saharan genes that hitchhiked along with genes that had superior disease resistance.

            Unproven? yep. Highly highly controversial? absolutely. Probable? yes but better keep those thoughts to yourself unless your are hiding behind an alias on one of a few select blogs 🙂

  9. Anonymous says:

    “Some retards (British papers) have been spinning this as saying that there are big benefits to mixed-race marriage.”

    Retarded like a fox. Which story do you think is going to get more clicks?

  10. There is the obvious reason of touting mixed-race marriage for political popularity. As to the science, I think there is general misunderstanding of threshold phenomenon. If marrying someone from the next town is good mixing, then marrying someone from another continent must be better still, they think. It’s not a crazy theory. But when you look into it and see how little mixing fills the “enough difference” glass, that should be the end of it.

    The negative effects of inbreeding might get tricky in heavily stratified societies that have only a few elites at the top. Marrying your first cousin might give your progeny an average loss of 0.3sd IQ points. But marrying one of the drones or worker bees might be worse.

    • dearieme says:

      “in heavily stratified societies that have only a few elites at the top”: surely such a society typically has only one elite at the top?

  11. Aggh. Should be “phenomena.”

  12. RCB says:

    There’s a great section on inbreeding in the recent Evolutionary Genetics book by the Charlesworths. A lot of it is aimed at detecting whether the effect is due to rare deleterious recessives or to heterozygosity reduction. The main test is to see how much fitness (or any quant trait) is reduced in the inbred relative to the pop mean. I think the intuitive argument goes like this: If inbreeding effects result mostly from reducing heterozygosity, then the drop in fitness is relatively small, as compared to expression of rare recessives. That’s because segregation ensures that a lot of outbred people will be enduring the bad effects of homozygosity already (think sickle cell). Inbreeding just increases the number of homozygous loci. If it’s rare deleterious recessives, then outbred folks will suffer very little (the square root of a small number is very small), but inbreds will potentially suffer a lot. This can be made quantitative.

    Something like that. Anyhow, the result I remember from the book is that rare deleterious recessives are found to be more important in most studies. Will have to check on that.

  13. RCB says:

    But what I really find interesting about inbreeding is that all its bad effects can be removed in one generation of outbreeding. You can marry the most inbred hillbilly in the Appalachians (excuse the stereotype; not sure if its true); as long as you’re not from around there, your kids will be fine. That’s counterintuitive

  14. bispora says:

    It seems ashkenazim know the trick how to balance the harmful effect of inbreeding while maintain the fitness gain

    • ohwilleke says:

      Ashkenazim populations are without exception admixed with neighboring populations, although the period of time during which that was common is often lost to history or memory.

      Also, to the extent that Ashkenazim were an exceptionally fit population compared to the locals that they encountered in the diaspora whom they could marry given their low social status despite the downsides of inbreeding depression, and also needed to maintain community cohesion without employing formal legal means that were not available to them, cousin marriage may have been the best choice available to produce fit children, and to bind the community together so that it could continue to exist with family ties that strengthened ethnic ties.

      Also, suppose that you are a young woman in an Ashkenazim community in a small village in the diaspora and there are only three eligible males available to marry, because your non-Jewish neighbors wouldn’t marry you even if local religious laws didn’t forbid it. Because the community is small, two of them are cousins, and one of them, who is not a cousin, is a widower who beat his previous wife and showed her no respect. Wouldn’t you want cousin marriage to be legal?

      I suspect that an important part of the calculus made in the Muslim world at the time that cousin marriage was widely adopted as a cultural practice was that the fitness enhancement that came from having a clan of people tightly bound to be loyal to you from tight family ties created by cousin marriage (in a society with rampant corruption and a weak state) outweighed the acknowledged downsides of inbreeding depression. It is a group fitness v. individual fitness trade off.

      • Fourth doorman of the apocalypse says:

        Because the community is small, two of them are cousins, and one of them, who is not a cousin, is a widower who beat his previous wife and showed her no respect.

        Are you telling us that it was common?

        • ohwilleke says:

          I’m telling you that it choices like that happen in small communities. And, yes, the language in bold was very common in almost every culture for almost all of history.

  15. Whyvert says:

    @James Thompson “The 4.5 IQ points for first cousins is interesting, and shows how lots of ROH could explain very severe drops in intelligence with repeated cousin marriage”

    Is it reasonable to say that 2 generations of cousin marriage would bring drop 9 IQ points (on average), and so on?

    • RCB says:

      Good question. You could assume that the penalty is proportional to the increase in homozygosity. Pop. Geneticists have worked out the rates of approach to homozygosity for various inbreeding systems. Combine those two and you’d get the answer. In any case, the penalty would have to eventually level off as homozygosity reached 1. Perhaps quite quickly under high inbreeding. So wouldn’t drop by a full 4.5 points every time.

    • Mohd Fareed and Mohammad Afzal. Estimating the Inbreeding Depression on Cognitive Behavior: A Population Based Study of Child Cohort. Published: October 14, 2014. DOI: 10.1371/journal.pone.0109585. It is only one paper, but a very interesting one. It suggests an even higher rate. Here are my comments:

  16. ohwilleke says:

    The reason to support first cousin marriage is that the inbreeding depression downside while real, is not so insurmountable that the children of first cousins who are bound and determined to be wed (or married for cultural reasons whether they wanted to or not, perhaps someplace where it was legal and even mandated and now have children together as a result) are better off with married parents in a household that is legitimate, than being raised without a parent who genuinely loves them and their other parent, despite state objections. Policy makers can reasonably decide that leaving this suboptimal choice open does less harm than banning this choice, given that the downsides, while real, are not overwhelmingly catastrophic as they are in inbreeding circumstances that are banned by incest laws that are nearly universal. Law making is about drawing lines even when there is no absolutely clear boundary.

    As the original post notes, inbreeding depression produces fewer downsides than marrying someone who is not inbred, but is shorter and significantly less intelligent. If you and your cousin are both tall and smart relative to the other choices in your particular marriage market, inbreeding depression may still lead you to conclude that cousin marriage will produce smarter, taller children than the alternative. We assume that the choice of non-inbred spouses is effectively infinite, but that is sometimes not the case for a particular person in a particular place.

    To take another example, in places with adequate police protection, owning a handgun is statistically a horrible decision. But, given that the law provides no means to compel police to protect you if they choose not to (even for improper reasons), legalizing gun ownership provides a private backstop to the failure to the police to do their job for people who are in that situation and face genuine serious risks of an armed attack. Policy makers are particularly likely to allow people to make bad choices when the choice that is bad for most people is the best available choice for a few people.

    Part of living in a society where free choice plays a central role is tolerating the fact that some people are inevitably going to make bad choices when given the freedom to do so. For the same reason, tobacco smoking is legal, even though it is surely much worse for you and your children than cousin marriage, because the social downsides of trying to restrict this freedom using the criminal justice system would be worse.

    Is it so hard to recognize that there are categories of behavior that should be discouraged without being banned?

    For example, polygamy has that status in most Muslim societies where it is legal. Islam simultaneously allows men to have up to four wives as a matter of religious law, and simultaneously discourages men from having multiple wives as a matter of religious wisdom and doctrine, mostly through warnings about the difficulties involved in treating each of multiple wives equally.

    Tobacco is legal, but has to bear warning labels, has highly regulated sales to adults only, and is heavily taxed with funds used in part to discourage people from using tobacco.

    • Rick says:

      “children… are better off with married parents in a household that is legitimate, than being raised without a parent who genuinely loves them and their other parent”

      Is this true? I have heard thousands of arguments on this blog with evidence to the contrary.

      I think the standard response is that nature/genetics determines 75% and the rest is some random unknown factors.

      So, I would assume that based on the obviously unbiased nature of the commentary here, that this claim is total BS.

      Parents who love each other doesn’t matter. It’s only if they were cousins that matters in the long run.

      • ohwilleke says:

        Children raised by single parents in the U.S. and most other places, are disprortionately in or near poverty.

        The frequency of abuse or neglect of children in a household with a birth parent and an unrelated (to them) adult, on average, is much higher than a child raised by genetic relatives, particularly for preschool age children where abuse and neglect rates generally are the highest. This probably doesn’t hold true in cases of adoption, however, where there is considerable pre-screening of prospective parents.

        • jamesd127 says:

          In a step family, you have one parent who loves you, and one “parent” who wants to kill you.

          In an adoptive family, both parents treat you like a pet, rather than a real child. Not clear which is better.

        • Rick says:

          But how does this have any effect on anything besides the happiness of a child?

          Most of the comments I have seen here would suggest that it is the genetics that result in a continuation of the poverty and abuse and neglect cycles, not growing up in a poor, abusive, or neglectful environment.

          Cousin marriages cause a genetic situation. Unloving parents cause an environment that seems to make little difference in life outcomes.

          Or am I wrong about this? I am just basing this on what I have read here.

        • jamesd127 says:

          Within the range of normal intact families, environment does not make a lot of difference. On the other hand there is a significant likelihood that a step parent will do something like grabbing the kid by its feet and whirling it through the air to bang its head on the bedpost, in which case environment will make a significant difference.

          • Rick says:

            “there is a significant likelihood that a step parent will do something like grabbing the kid by its feet and whirling it through the air to bang its head on the bedpost”

            I would love to see the data that suggest that ‘significant likelihood’.

            This is completely untrue. You might as well rule out any families with more than one child. Older siblings are significantly more likely to damage their younger siblings than step parents are.

            • jamesd127 says:

              I would love to see the data that suggest that ‘significant likelihood’.

              Obviously no such data can be collected, since it would contradict the ideology that the destruction of marriage is a good thing, and taking children away from their fathers is a good thing.

              Personal observation suggests a high level of near homicidal violence by boyfriends against their girlfriend’s children, though you would doubtless argue that this is far too small a sample, inadequate, reflects economic stresses, inadequate child support payments, a society that is insufficiently supportive of single motherhood, etc.

              However, in the ancestral environment, and indeed in the present environment, it is in ones genetic interest to kill one’s step children. A step child is a greater competitor for one’s wife’s or husband’s resources than someone else sleeping with one’s wife or husband, and it comes as no surprise that people wish to kill such competitors, and, given the opportunity, frequently do so.

              Evolutionary psychology predicts the same response to a stepchild, as to a man sleeping with one’s wife.

          • Cloudswrest says:

            Although I understand Woody Allen loved his stepchildren.

          • JayMan says:


            “Within the range of normal intact families, environment does not make a lot of difference. On the other hand there is a significant likelihood that a step parent will do something like grabbing the kid by its feet and whirling it through the air to bang its head on the bedpost”

            You must have a meaning of “significant likelihood” that is completely different from mine.

  17. TWS says:

    How much did bringing in slave concubines from Europe and Africa help to ameliorate this for the Islamic societies? Were the concubines too few to make a difference in the gene pool? This mostly ended some decades ago are the same societies that practiced the slavery the same ones with the cousin marriage problems? There’s a Jewish group that allows uncle/niece marriages wouldn’t that have the same effect?

    • jamesd127 says:

      Uncle niece marriages were legal in Australia last time I heard. There is a lot of it beyond the black stump – and considerably worse beyond the black stump. However, they are socially forbidden, even beyond the black stump.

      • Peter Lund says:

        Uncle/niece and aunt/nephew marriages are legal in Denmark as well, although I’ve never ever heard of a single case.

        (“Of course you are not allowed to shag your sister ’cause that would be icky but go ahead and shag her daughter instead!”)

      • Fourth doorman of the apocalypse says:

        There is a lot of it beyond the black stump – and considerably worse beyond the black stump.

        Hmmm, please give us more of the salacious details. I lived there for 40+ years from birth and grew up in a working class family but didn’t see any of it so it would be fun to find out about it now.

      • TWS says:

        Ugh! But I did have that one cute cousin. ;>). I had a coworker that admitted to shagging her first cousin and my wife had two of her cousins marry. They were unable to bring any of their pregnancies to fruition. All were stillborn.

        On a nearby rez there are two double cousins that have had two children together. Their oldest was a very ‘slow’ girl and the youngest was a boy with ridiculous physical strength from a young age (although it runs in the father’s family, well I guess both families). The boy’s a teenager and built like strongman competitor. He does little but play video games and occasionally lift the back ends of cars or heavy boulders to impress the other kids.

  18. Bob says:

    Is there anything to Steve Sailer’s idea that 3rd cousin marriages are a Darwinian sweet spot?

  19. Charles S. Brown says:

    Einstein married his first cousin. One of his sons was an accomplished engineer, another spent his last years in a Swiss asylum with an apparent schizophrenic disorder.

    • Just saying says:

      Einstein was actually married to a Serb of non-Jewish origins before marrying his cousin. The Serb was the mother these two. The schizophrenic son probably just got an unfortunate mix of alleles so not quite an inbreeding/outbreeding issue.

      • dearieme says:

        WKPD on his second wife: “Albert and Elsa were first cousins through their mothers and second cousins through their fathers.”

        On the other hand, there may have been something wrong with his daughter by his first wife, though what isn’t clear. There has been dark speculation about what happened to the girl, but without a shred of evidence that I’ve ever seen. WKPD again:

        Lieserl Einstein … was the first child of Mileva Marić and Albert Einstein. “Lieserl” was born in January 1902, a year before her parents married, in Novi Sad, Vojvodina, present day Serbia, and was cared for by her mother for a short time while Einstein worked in Switzerland before Marić joined him there without the child. “Lieserl’s” existence was unknown to biographers until 1986, when a batch of letters between Albert and Mileva were discovered by Hans Albert Einstein’s daughter Evelyn.

        The last time “Lieserl” was mentioned in their extant correspondence was in Einstein’s letter of 19 September 1903 (letter 54), in which he showed concern for her suffering from scarlet fever. His asking “as what is the child registered? [Adding] we must take precautions that problems don’t arise for her later” may indicate the intention to give the child up for adoption.

        As neither the full name, nor the fate of the child are known, so far several theories about her life and death have been put forward: Michele Zackheim, in her book on “Lieserl”, Einstein’s Daughter, states that “Lieserl” was mentally challenged at birth, and that she lived with her mother’s family and probably died of scarlet fever in September 1903.

        • Charles S. Brown says:

          Both of you are correct, I was wrong about the mother of the children. Of course, all of this is just anecdotal bullshit that may have no scientific significance anyway.

          • dearieme says:

            If out of Einstein’s three children, one was a mental defective, and a second a madman, do we draw any lessons? I wouldn’t, especially as I know little about his first wife.

        • Anonymous says:

          Tim Powers made an interesting book out of Lisearl.

  20. HL says:

    Polar bears can breed with brown bears to produce fertile grizzly–polar bear hybrids,[19][26] rather than indicating that they have only recently diverged, the new evidence suggests more frequent mating has continued over a longer period of time, and thus the two bears remain genetically similar.[25] However, because neither species can survive long in the other’s ecological niche, and because they have different morphology, metabolism, social and feeding behaviors, and other phenotypic characteristics, the two bears are generally classified as separate species.[27]

  21. Reblogged this on Philosophies of a Disenchanted Scholar and commented:

    I read in another study that 3rd cousins are the sweet spot for variance and to avoid outbreeding depression too. Think it was this one

  22. Greying Wanderer says:

    First cousin marriage was very common historically (h/t hbdchick) so I imagine the way it worked was have twelve kids and 2-3 will be healthy and survive.

    Irish Travelers are like that – they have a massive child mortality rate but because they have 10-12 kids the survivors are (more or less) physically healthy.

    “The birth rate of Irish Travellers has decreased since the 1990s, but they still have one of the highest birth rates in Europe. The birth rate for the Traveller community for the year 2005 was 33.32 per 1,000, possibly the highest birth rate recorded for any community in Europe.

    Some 10% of Traveller children die before their second birthday, compared to just 1% of the general population. In Ireland, 2.6% of all deaths in the total population were for people aged under 25, versus 32% for the Travellers.”

    I imagine this is how it worked in most places (including Europe before the big change in marriage practise) – lots of dead kids and a few healthy ones to produce the next generation.

    I assume the consequences of all this would be quite negative for the women.

    • Greying Wanderer says:

      So the situation with muslims now might be the unhealthy ones survive (cos medicine) and the parents don’t have enough in total anymore to produce 2-3 healthy one (maybe partly due the cost of providing for the surviving unhealthy ones).

      Seems to me making inbreeding work at all requires lots of dead kids and making inbreeding work to your advantage without the disadvantages would require a culling well.

      (before embryo testing that is)

  23. j says:

    Inbreeding depression stabilizes after a pair of generations, so a cousin-marrying population is sustainable on the long term. Say Israeli Beduins. In contrast, a strongly outbreeding population, say Ashkenazi with Ethiopian, will suffer from outbreeding depression that will increase through future generations. Somebody tell me I am wrong and/or to stop mentioning the issue.

  24. Bob says:

    What would be the ideal Fst value for mating? A dating service which paired couples by ideal value could be useful and popular. and 23AndMe and other similar services are popular, so I think there’d be lots of demand for this sort of thing.

  25. spare armadillo says:

    I had an Egyptian friend during my college daze who was really, really smart. He got a Ph.D. in EE from one of the highest rated departments in the country and has done very well since in the awl bidniss.

    He told me his parents were “double cousins”, so something like dad’s dad was a brother of mom’s dad, and dad’s mom was a sister of mom’s mom. He had 3 brothers, one of whom also got a Ph.D. in EE with the other 2 being MDs.

    My friend married an East Asian woman, so no inbreeding depression for his kids.

    • j says:

      Have you heard of outbreeding depression? When the genetic distance is so large that mixed progeny suffers from all kind of issues. But in case of European with East Asian there is no effect, not bad nor good, since we are very close.

      • spare armadillo says:

        “Have you heard of outbreeding depression?”
        Yes, I had heard of it. It was mentioned on this blog some time ago.

        But I think the remarkable thing about my friend is that he and his brothers were all very intelligent in spite of the inbreeding.

      • Bob says:

        Are Ashkenazim and Europeans closer to East Asians than to Ethiopians? I’m not sure if that’s true. I think they may be intermediate or closer to Ethiopians because of Ethiopians’ Semitic ancestry.

        Ahskenazim outbreeding with Ethiopians would result in lower IQ offspring, because Ethiopian IQ is lower. Lower IQ is certainly an issue, although I’m not sure if that by itself would be the result of outbreeding depression, since Ethiopians have lower IQs. I think you’d have to look at other indicators.

      • Rick says:

        Indeed, all humans are VERY close as compared to the variation in most other ape species.

        • jamesd127 says:

          “Indeed, all humans are VERY close as compared to the variation in most other ape species.”

          This is a PC fact and therefore should be regarded with extreme suspicion, much like hockey stick.

 indicates that differences between human races, though smaller than the difference between humans and chimps, is comparable to the difference between human chimps.

          Which is obvious just by looking.

          • Rick says:

            That is hilarious. Good one.

            • jamesd127 says:

              In “The Root of the Phylogenetic Tree of Human Populations” by Masatoshi Nei and Naoko Takezaki, Institute of Molecular Evolutionary Genetics:

              Table 1 shows that the genetic distance between a Pygmy and a Chinese is greater than the genetic distance between a pygmy in and chimpanzee, which you should have guessed just by looking at them.

              He has four different measures of genetic distance. The results for the other three are less shocking, but they are shocking enough. Every table has some wonderfully racist hate fact.

              It is the paper that just goes on giving.

              I particularly love the super racist figure 5, though it is an outlier, and the other figures are more likely to reflect reality. But the other figures are racist enough. As he incautiously observes “The rate of evolution may vary from population to population” – in other words, some populations are less evolved than others. Probably not by as much as figure 5 would indicate though.

          • Rick says:

            1996 was a long time ago. Try reading a paper with some actual data on the subject. Perhaps

            • jamesd127 says:

              “1996 was a long time ago. Try reading a paper with some actual data on the subject. Perhaps

              Which paper piously avoids measuring the distance between human populations by the same measure as the distance between humans and related species.

              Which curious silence tells us that if they were to make such measurements, the results would be as horrifying as the measurements made by Masatoshi Nei and Naoko Takezaki,

          • gcochran9 says:

            Untrue. No more of this.

  26. Patrick Boyle says:

    No mention by a commenter so far of the Habsburgs or Don Carlos – about whom Verdi wrote his wonderful opera. Nor any mention of any of the consanguinity problems of the Windsors or the other crowned heads of Europe – many of whom were married to their cousins or descended from such unions

    There are at least two Sherlock Holmes films based on the premise that the heir to the throne was Jack the Ripper – the grandchildren of Victoria were so notorious. Another one of them was the stammerer George the Sixth who seemed to also have a genetic malady. I’m the only one who seems to suspect that this too was another sign of consanguinity (Victoria married her cousin I believe). It probably only shows that my Irish heritage is only too ready to suspect the English. .

    • Ilya says:

      Actually, some speculate that many of the lethal mutations manifested by inbreeding depression were somewhat overcome by the Hapsburgs via purging selection, over about 150 years or so:

      Again, speculative, but interesting and somewhat plausible (given that it doesn’t disagree with H D King’s verifiable, strong results), but I don’t know Ceballos’s paper’s details to either agree or disagree.

    • dearieme says:

      It’s not even clear there was a Jack the Ripper. Once you’re into the era of the popular press, anyone can copy-cat a well publicised murder. For evidence, see almost any American mass murders such as the recent one in the church.

  27. Pingback: This Week in Reaction (2015/07/05) | The Reactivity Place

  28. George says:

    Man, this blog is such a testament to racist loserdom. This blogger really seems to have a knack for taking a really interesting, active area of research like heterosis and turning it in to ye olde whinge about IQ, interracial marriage, etc…

    • Erik says:

      World: “race race race race race”

      Blog: “technological collapse, adaptation natural selection, population spread, and the world is wrong about race”

      World: “Why do you keep whinging about race? You must be a racist loser.”

    • Fourth doorman of the apocalypse says:

      Are you suggesting that vaccinations cause homosexuality?

      That would certainly give the anti-vaxxers some interesting ammunition although Let Us Pray It Does Not Become Widely Known

  29. Ilya says:

    @Everyone: sorry, it’s possibly cheating, but does anyone have access to ?

    It looks like it could be a pertinent, interesting paper. I’d appreciate if someone forwards it to me… or at least summarizes the findings ;-).

  30. Pingback: linkfest – 07/12/15 | hbd chick

  31. Mark F. says:

    “Naturally, enlightened opinion increasingly supports legalization of first-cousin marriage, due to its usual ignorance, perversity, and nihilism.” But first-cousin marriage is only illegal in some states in the United States, no place else. It’s legal in California, and is not a political issue, maybe because the number of such marriages is small.

  32. Pingback: Inbreeding | John Drake

  33. Steph says:

    Articles like this get on my nerves, so let’s put this into practice. According to this children of first cousin marriages are shorter and have lower IQ’s. Well my Grandfather was the product of a 1st cousin marriage, he was 6 foot tall with a Genius IQ and taught mathematics and technical drawings for Engineering. Explain this??/

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