Who's the dad?
Most mornings while I drive to work, I pass a nearby Walgreen’s. I was last in there to get allergy medicine. But not too far from those shelves where the Benadryl is stocked there is a DNA-based paternity testing kit. In between sneezes and taking pills, I can also collect a sample, obtain another from a putative child, and then send these in to find out in two days if my DNA is consistent with being the child’s father. That’s the latest in ways (apart from comparing phenotypic traits or using educated guesswork) to discern whether one is a likely genetic father to a child.
If you are an Azara’s owl monkey father, you might find these technical steps a waste of time. Rather than collect biological samples for genetic analyses, you’d let human researchers do the work for you. You’d also learn that if you were in a socially monogamous relationship in which an offspring had been born, you were in fact the genetic father. These are conclusions from a new study on wild pair-living owl monkeys from the Gran Chaco in Argentina. In work by Maren Huck, Eduardo Fernandez-Duque, Paul Babb, and Theodore Schurr, samples from 128 individual owl monkeys, representing 30 group-living or floating males, along with mates and offspring, were obtained. The genetic analyses failed to identify any cases of non-paternity. In other words, the behavioral observations of social monogamy among owl monkeys map on to genetic monogamy. That’s news (and bad news to any company that would seek to sell paternity testing kits to owl monkeys).
As data have accumulated in recent decades from wild birds and to a lesser degree mammals, scholars learned that a variable fraction of offspring in socially monogamous species were fathered by extra-pair mates. While about 90 percent of bird species are socially monogamous, a 2002 review showed that about 90 percent of those species exhibit extra-pair paternity, with an average of about 11 percent of chicks fathered by extra-pair mates. Among primates, researchers observed socially monogamous gibbons sometimes “cheating” on partners with extra-pair mates, and genetic data confirmed the occasional extra-pair paternity case; the same has been true among several species of socially monogamous lemurs. This new study on owl monkeys thus represents the first species of primate in which true genetic monogamy has been documented in the wild and with a sizable sample.
Another contribution of this new study is a comparative analysis of 15 species of socially monogamous mammals, investigating degree of extra-pair paternity in relation to pair-bond quality (intense/dispersed) and male care (intense or not). Intense male care was associated with less extra-pair paternity, but pair-bond quality was not. As the paper notes, it is an open question whether to see higher likelihood of paternity causing more intensive paternal care, or more intensive paternal care increasing the likelihood of paternity. That said, these owl monkeys join the ranks of a select few species of both socially and genetically monogamous mammals including Kirk’s dik dik and the California mouse.
What about humans? The fact a would-be father can purchase a paternity-testing kit, or be told that the child looks like him, suggests that extra-pair paternity is part of many men’s concerns. Many medical textbooks suggest that about 10 percent of men who think they are the genetic father are not in fact the father. In arguably the most synthetic analysis of human non-paternity, Kermyt Anderson collected data from dozens of studies, yielding 67 estimates of genetic non-paternity. For “high paternity confidence” samples (samples in which a father likely assumed he was the dad), about 2 percent of fathers had children sired by other men. For men with “low paternity confidence” (such as men using commercially available testing kits), approximately 30 percent of offspring were fathered by other men. The upshot is that giving a single human statistic masks the variation across samples and individuals in extra-pair paternity, but that for men who think they are a child’s genetic father the chance is very likely that they are.
In summary, this new study contributes to a richer view of a father’s fidelity. Owl monkeys represent the poster child of genetic monogamy among primates, and the study also links intense male care with lower rates of extra-pair paternity across socially monogamous mammals. That’s plenty for human fathers to contemplate as well.
Anderson, K.G. (2006). How well does paternity confidence match actual nonpaternity? Results from worldwide nonpaternity rates. Current Anthropology, 48, 511-518.
Gray, P. B. & Anderson, K. G. (2010). Fatherhood: Evolution and human paternal behavior. Cambridge: Harvard University Press.
Griffith, S.C., Owens, I.P.F., & Thurman, K.A. (2002). Extra pair paternity in birds: a review of interspecific variation and adaptive function. Molecular Ecology, 11, 2195-2212.
Huck, M., Fernandez-Duque, E., Babb, P., & Schurr, T. (2014). Correlates of genetic monogamy in socially monogamous mammals: insights from Azara’s owl monkeys. Proceedings of the Royal Society of London B, 281, 20140195.