Paternity certainty is high in most human societies

A new paper in Current Biology reiterates what we know, A Historical-Genetic Reconstruction of Human Extra-Pair Paternity:

Paternity testing using genetic markers has shown that extra-pair paternity (EPP) is common in many pair-bonded species…Here, we use a population-level genetic genealogy approach [6, 8] to reconstruct spatiotemporal patterns in human EPP rates. Using patrilineal genealogies from the Low Countries spanning a period of over 500 years and Y chromosome genotyping of living descendants, our analysis reveals that historical EPP rates, while low overall, were strongly impacted by socioeconomic and demographic factors. Specifically, we observe that estimated EPP rates among married couples varied by more than an order of magnitude, from 0.4% to 5.9%, and peaked among families with a low socioeconomic background living in densely populated cities of the late 19th century. Our results support theoretical predictions that social context can strongly affect the outcomes of sexual conflict in human populations by modulating the incentives and opportunities for engaging in extra-pair relationships [9, 10, 11]. These findings show how contemporary genetic data combined with in-depth genealogies open up a new window on the sexual behavior of our ancestors.

The key thing to note that the 5.9% EPP rate is lower than the urban myth often promoted that 10% of children don’t realize the father raising them is not their biological father. The figure at the top illustrates the differences. You see that EPP is higher in low socioeconomic instances. The authors also found that higher density and urban areas were correlated with EPP.

Basically, prosperous farmers in less dense areas are the least likely to exhibit EPP. I think the Dutch study probably generalizes to most Eurasian societies. In particular, the male-dominated peasant societies that emerged in the last 10,000 years have likely been characterized by low EPP. Of course, there are societies with higher rates in the anthropological literature, but as noted in this paper those are societies characterized by more polyandry.

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5 thoughts on “Paternity certainty is high in most human societies

  1. Possibly addressed in the full paper, I’d be interested to know if they checked out whether mtdna lines were consistent as well.

    Finding surname/genealogical tree non-consistent y-dna *could* be non-paternity, but it also could be reflecting adoption and poor record keeping of adoption, the latter of which we’d expect to see among low SES as well.

    You might also find cases where mt is consistent, but where actually widows or abandoned or never married women have re-married and their children end up with a new father, and the original father is not reflected by genealogical trees due to “hushing up” or just poor record keeping. But again, this isn’t a extra-paternity event as such in the sense of an extra-martial event.

    Basically, is the raw rate just reflecting genetic non-paternity, or specifically genetic non-paternity which they are *certain* is due to extra-martial reproduction?

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  2. Actually, in a previous study by this author (Maarten Larmuseau), he says some of the non-matching Y chromosomes could be due to adoption – in particular, grandparental adoption, whereby if a young girl got pregnant out of wedlock, her mother would pretend that the resulting child was hers (the grandmother’s). That used to happen in Sicily and Ireland, places where an unmarried woman’s pregnancy could bring disgrace to her whole family. Even in less stringent countries, like England, such “grandparental adoption” occurred. There was always some confusion about “oldest mothers” in the Guinness Book of World Records because some of these older mothers were really the grandmothers to the children in question.

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  3. They did check birth records (in civil registries in the last two centuries and in church books earlier), and made sure the birth happened after marriage, and that the child wasn’t disowned later. Perhaps some of these records were hidden adoptions, but at least any such adoption events were well masked. This stringent filtering, potentially, leads to underestimation of the rate.

    On the other hand, the dataset is so thin that it may have been led astray by biases or fluctuations, especially in the older era. There were just 96 non-paternity events, and most of them weren’t dated. Half of the family trees didn’t start until late XIX c. and a quarter – only in the XX c. Once you drill down to specific subcategories – “low density farmers” or “urban poor” – there may hardly be any NP events left in the XIX c. timeframe.

    To draw the nice scatterplot above, they use a logistic regression, using population density and social status, but not year of birth. The hundreds dots look like a lot of data, but in actuality each of these dots comes with a confidence interval which may be as wide as the screen.

    The social class effect seems to be real (if it isn’t augmented by some unexplored confound, like perhaps by the lower-class pedigrees being “younger”), but the order-of-magnitude size of the effect can’t be assured.

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  4. Great paper and it clearly shows that the upper limits for NPE are far lower than the overestimated, actually completely ridiculous exaggeration some feminist oriented extremists wanted to sell. They even tried to convince people the close to 10 percent were present in all societies. Even strict patriarchal ones were expulsion, torture or death were the consequence of such a behaviour – and this was the rule in most higher cultured societies.

    I would add that the cause “social class” is an euphemism for what’s really happening. Because it is obvious that in the lower social classes, to say it blunt, there is an aggregation of negative genetic and social traits less common in the middle and upper classes.
    Its a higher frequency of e.g. psychological disorders, lack of personal control and discipline, inability to plan and think ahead, low intelligence, low education and general lack of knowledge (including birth control) and of course, probably the most important single factor: Substance abuse and absent fathers.
    But to stress it strongly: Only a higher frequency.

    A large portion of the women which gave birth to a “mailman’s child” in a marriage have some kind of deficit. Most certainly not all, because they might have been forced into a horrible relationship and got pregnant in an extraordinary romantic love-relation and so on. But fact is, that is rarely the case, the woman having issues is the norm.

    If looking at and speaking with some of the mothers which were unfaithful, got pregnant, kept the child, gave birth and kept the true father a secret and are not lower level, they are quite often rather sociopathic personalities. But this is the minority, which is present in all classes but doesn’t count too much.

    The majority are uncontrolled, unintelligent, often psychologically affected women, living under bad circumstances and doing some sort of substance abuse. Alcoholism is rampant under such people, so is a lack of educational effort. The children display behavioural problems early on and the most obvious trait of the parents is mental dullness.

    If you cut off significant psychological deviations, low IQ and families affected by substance abuse, I guarantee that even for the lower social classes the rate would drop drastically, very drastically. Its just that most of these people fall into this category of “low social class”, because their character doesn’t align well with middle and higher class demands.

    But the more decent and functional lower class families are almost as unlikely to have a “Kuckuckskind” (“cuckoo-child”). Is that term known in American English? Its the best description of the problem, considering how a cuckoo is behaving.

    I might add that in a lot of such “families” the husband actually knows he is not the biological father. But these couples are often preoccupied with other personal problems so much, that this is not even the biggest problem they are facing. Quite often both are so dull, they don’t care about many things others might take as highly important. Similar to mentally impaired people in general.

    “They did check birth records (in civil registries in the last two centuries and in church books earlier), and made sure the birth happened after marriage, and that the child wasn’t disowned later.”

    Is that true?
    That’s a big problem for the numbers, because more intelligent fathers will usually see or otherwise find out that the child is not theirs. Or more ethical mothers might at some point tell the truth, the husband, but the child in particular. So it might come up.

    This would really distort the result for the middle and upper class to some degree, since they lack stupidity and dullness, while there is every more reason to care for disinheritance. Because in the dysfunctional families at the bottom I described earlier, there is actually little reason or energy to care for the inheritance anyway.

    So how many of the children were disowned would be of great interest.

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  5. Just a question: do you know of any non-paternity studies performed in Asian countries? I suspect the percentage would be low, but I was wondering if there was any backing for that feeling.

    Thank you

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