How paternity testing is like international trade

Nonpaternity rate % N
Switzerland 0.83 1607
USA, Michigan, white 1.49 1417
USA, California, white 2.1 6960
USA, Hawaii 2.3 2839
UK, West London 3.7 2596
Paternity Testing Laboratories
UK 16.6 1702
USA, Los Angeles, white 24.9 1393
Sweden 38.7 5018
South Africa, Cape Coloured 40 1156

The results above are from Kermyt Anderson’s How Well Does Paternity Confidence Match Actual Paternity? This is still one of the best surveys of the field, despite being 12 years ago. A more recent paper, Cuckolded Fathers Rare in Human Populations, uses more powerful genetic genealogy methods to come to the same conclusion as Anderson’s survey: extrapair paternity, or nonpaternity events, are rare in Western societies. I don’t think it is limited to Western societies. I suspect that when high throughput sequencing is applied to Chinese clan lineages and Hindu gotras, you will found that nonpaternity events are similar to those in the West.*

On the other hand, in some small-scale societies, the rates are much higher.

I won’t delve into the evolutionary anthropology here. Rather, I want to point to a new paper, Growth of ancestry DNA testing risks huge increase in paternity issues. Ancestry testing is huge. Within the next year, it is almost certain that 10% of the American population when having some sort of high-density genomic testing done.

As the author of the paper pointed out to me on Twitter, 1% of 16 million people is still a lot. Yes, in absolute terms. But we need to look at the other side of the equation.

In Anderson’s original data one of the interesting results is that in most datasets drawn from paternity testing laboratories, where there is a very high suspicion of nonpaternity events, most of the fathers nevertheless were biological fathers! In a nonpaternity testing context, nonpaternity events will be much closer to ~1%. But, I think it is reasonable to suppose that some of the 99% of the fathers who turn out to be biological fathers also have suspicions…which are unfounded.

Like free trade, you tend to see one side of the equation much more than the other. In free trade scenarios, a minority of workers may lose their jobs or have to work under reduced wages, but the vast majority of consumers will get cheaper or better products. The former is much more salient than the latter.

Similarly, the small minority of fathers and families who are going to be “surprised” in a negative way, is balanced out by the likely larger number who have low-grade suspicions, but in fact, are confirmed in their biological relatedness.

Addendum: Needless to say, if you are part of the “cuckold community”, you should probably not getting this sort of testing.

* The necessity of good quality whole-genome sequencing is due to the fact that male relatives are excellent candidates for nonpaternity events. To get a certain estimate one would want to count unique mutations across the pedigree.

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

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).