Paternity certainty is high in most human societies

Posted on November 15, 2019November 15, 2019 by Razib Khan

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.

Napoleon Chagnon, R.I.P.

Posted on October 2, 2019October 25, 2019 by Razib Khan

Napoleon Chagnon has died. It is unfortunate that Chagnon is known to many for the fact that he became involved in a controversy triggered by the activism of a polemical journalist. It will surprise none of the readers of this weblog I agree with Alice Dreger’s take on the whole issue.

If you want to familiarize yourself with Chagnon, I would recommend Noble Savages: My Life Among Two Dangerous Tribes — the Yanomamo and the Anthropologists. It was written at the end of Chagnon’s life, so it summarizes his research and overall views.

I will be frank and state that I am much more skeptical of the generality of some of Chagnon’s inferences using an evolutionary psychological framework than I was 20 years ago. If Chagnon’s critics had focused more on the science everyone would have benefited. As it is, they went the easy route with political food fights.

Chagnon asked the right questions, even if I now judge that he came to some wrong answers. Such is science.

The cuckoldry rate in complex agricultural societies is probably ~1%

Posted on September 24, 2017September 24, 2017 by Razib Khan

One of the most interesting and strange things I’ve ever posted about has to do with extra-pair paternity rates. Basically, the rate of cuckoldry.

I first got interested in the topic because people kept bringing up the chestnut that 10% of children have misattributed biological paternity. That is, their biological father is different than the father who raises them. This is a “fact” I’ve encountered from many biologists and the public. But like the “fact” that you use only 10% of your brain, this seems more an infectious meme than a true fact.

The problem with ascertaining paternity is to get a representative sample. And, to get deep time depth you need good genealogical records. With genetic analysis new methods also came to the fore: analyzing the distribution of Y chromosomes within a lineage.

As far back as the middle 2000s Anderson had published How Well Does Paternity Confidence Match Actual Paternity?, which surveyed the literature and found that the rate of misattributed paternity was closer to a few percent than 10%. Later work found results closer to ~1% in places like Western Europe.

A new paper out of the Netherlands confirms this figure. This turns out to be the same proportion as in Flanders, just to the south. The authors wanted to compare the results with Flanders because it is an adjacent area with the same ethnicity (Dutch), but which went through industrialization much more quickly. Therefore it was a test of hypotheses about urbanization and extra-pair paternity.

How generalizable are these results? It seems entirely likely that the 1% figure applies across the Eurasian oikoumene (genotyping and surname analysis in China has found a similar number). And yet if extra-pair paternity is so low why are there so many cultural strictures on mate guarding in these societies?

Much of the above paper discusses the evolutionary psychological mechanisms which evolved to combat cuckoldry and the arms race with occurred as females sought “higher quality” sperm donors. In short, if paternity uncertainty is so minimal then presumably this is not a major recent evolutionary pressure.

The curious thing about these results, which are replicated in numerous studies, is the denial they elicit. There is an online “cuckold community” which does not appreciate that their fetish is not as common as the old 10% number implies (I know about this community due to referrals from message boards). Then there are “men’s rights” activists, who simply can’t believe that women exhibit such fidelity. Finally, there are the sorts who wish to tear down bourgeois sexual norms, and valorize a past which did not exist.

But the ultimate question has to do with human nature and modal behaviors in the past and across different societies. These results establish that low misattributed paternity societies can exist at equilibrium and that they are rather common. They do not establish this was the “environment of evolutionary adaptedness.” We simply don’t know enough about this topic, but, I do think there needs to be an appropriate synthesis between the evolutionary psychological outlook exemplified by The Blank Slate and the cognitively informed behavioral ecology found in The Secret of Our Success.

My own suspicion is that human cultures and behavioral scripts exhibit discrete modalities, but we’re mildly flexible. An economistic “modes of production” analysis would probably smoke out differences. More precisely I think the more economic independence that women in a society have the more likely paternity certainty is going to be a major issue because many men will reduce their investment to any given offspring. Although such economic independence is often conceived of as a modern development in gender relations, there are actually societies where women have been the dominant primary producers, because of a less intensive, more extensive, sort of agriculture (ergo, less premium on physical strength).