One of the peculiarities of human historical genetics is that people can simultaneously accept the existence of aggressive polygynous males such as Genghis Khan, and promiscuous females who give rise to the idea that 1 out of 10 children have an incorrect assigned paternity. I’ve mentioned the cuckoldry myth before. It is a common evolutionary myth; I’ve heard many biologists quote the 1 out of 10 number, and have often made myself obnoxious by pointing to the contradictory literature in this area. This isn’t to say that cuckoldry doesn’t exist. There’s certainly an evolutionary reason so many males engage in “mate guarding.” But you don’t need a high frequency of a trait to allow it to be selectively constrained. If it’s deleterious, then it will be driven down in frequency rather quickly. Whenever you get outbreaks of males who are sanguine about providing resources for offspring who are not their biological issue, natural selection will kick in and guarantee that this generous spirit toward their cheating partners and the delinquent cads does not persist.
The way that modern genetics adds value to this area is that one can compare Y chromosomal lineages to surnames. The logic is simple. If you have a constant frequency of misattributed paternity per generation over time the correlation between a surname and a Y chromosomal lineage will weaken. In addition, because the interlopers are likely to be different from each other you’ll have a pattern with (for example) ~50% of the male individuals of a given surname may carry one haplotype, while the other ~50% are distributed across hundreds of other haplotypes (one can imagine twists on the scenario, for example an early interloper might result in a secondary highly frequent haplotype).
So here’s an new study to bury this tired old urban myth, Low historical rates of cuckoldry in a Western European human population traced by Y-chromosome and genealogical data:
Overall, our results provide the first large-scale, unbiased genetic study of historical EPP rates in a human Western European population, with two independent estimation methods giving largely concordant results. Using the most direct estimation method, based on pairs of males that had a GCA in the last few centuries, we estimated the average EPP rate at 0.91% per generation (95% CI: lower bound 0.41% and upper bound 1.75%). This method took advantage of the hypervariability and mutability of Y-STR haplotypes, and the high phylogenetic resolution of the used Y-SNP haplogroups, which allowed paternally unrelated males to be easily recognized as such . In addition, using a second method that was based on the population genetic traces of a past immigration event which happened at the end of the sixteenth century, we estimated the EPP rate at around 2%. Although this estimate had a broader CI (upper 95% confidence limit = 8%), the actual estimate was close to the first one.
Both of our methods therefore estimated a substantially lower historical EPP rate for Flanders than the 8–30% per generation suggested by previous studies based on behavioural data on rates of EPCs in Western Europe and given the absence of reliable contraceptive methods [30–33]….
It’s open access, so read the whole thing if you aren’t convinced.
The authors are clear that this is from a sample in Flanders, but I do not find that this population should be that exceptional across the Eurasian Ecumene. In other words, I’ll be willing to put down money that Indian gotras and Chinese patrlineal clans will exhibit the same pattern of cuckoldry frequency. Additionally, the authors note that this pattern of high paternity confidence is paired with male investment in offspring. That seems relatively typical among many members of our species, though the extent seems to vary by population and environmental condition.