Why is paternal investment so rare in the animal world? Why do some human fathers choose the caring route, while others don’t? Biological anthropologist Richard Bribiescas, author of How Men Age: What Evolution Reveals About Male Health and Mortality, reveals how many of the physical and behavioral changes that we negatively associate with male aging may have actually facilitated the emergence of positive traits. These traits, including how we parent, have been crucial to our success as a species. We caught up with Richard for a special Father’s Day Q&A.
Many in the animal kingdom aren’t noted for being the best fathers. What’s the evolutionary significance?
Chimps aren’t very good fathers. They just aren’t. They don’t care for their offspring, provide food, or offer any assistance to moms. Don’t get me wrong, chimpanzees are noble creatures who merit our stewardship as well as the common courtesy of not destroying their forests. They’re just not the fatherly type. In fairness to our great ape cousins, most males in the natural world won’t be earning waffles in bed. With a few exceptions such as certain South American monkeys 1, most mammalian males are unlikely to earn a “World’s Best Dad” coffee mug on Father’s Day. Men however can be terrific dads with paternal care being one of the hallmarks of our species. Human males often invest significant amounts of time and resources in their offspring. This is true in modern industrialized societies as well as hunter/gatherer groups. Pass the butter and maple syrup.
Why is paternal investment so rare in the animal world? There are several evolutionary reasons but one especially salient explanation is that caring for offspring requires knowing who your offspring are. This is known as paternal uncertainty and is evident in all species that have internal fertilization. In humans, estimates of paternal misidentification when asking individuals to identify their fathers and then testing that assumption genetically ranges from one to around ten percent, depending on the study and population 2. Conservatively that means for every hundred readers, at least one of you was fathered by a man who is not the recipient of your Father’s Day card. But don’t freak out. This simply means that women are just as likely as men to evolve a range of reproductive strategies. Plus the odds are still in your favor of being correct so there’s no need to forward the mail.
A recent finding that illustrates the evolutionary significance of paternal investment is the capacity for men to display different reproductive states. This has long been observed in women since non-pregnant, pregnant, and lactating states are readily visible with numerous associated hormone changes. In men, different reproductive states are less obvious but evident when you look at reproductive hormones such as testosterone. Anthropologists Peter Gray and Lee Gettler have demonstrated this in numerous cross-cultural studies that show testosterone declines in response to fatherhood 3,4. This is more evident when men are in paired relationships with women.
Then what about male/male relationships and gay fathers?
Good question. We’ll get to that in a bit. So what is the significance of lower testosterone in association with fatherhood? It is still unclear but declines in testosterone may have behavioral, immunological, or metabolic effects that promote paternal investment. Stay tuned.
But fathering children is not the same as being fatherly. Again, hormones provide a spiffy way of getting at this subtle but important point. Anthropologist Martin Muller and colleagues looked at testosterone levels in association with fatherhood in two African societies, the Datoga who are cattle herding people in which the men do not commonly engage in childcare and the Hadza, an adjacent population of hunter/gatherers in which the men regularly hold and care for their children. Testosterone levels were not significantly different between the two populations even when looking at paternal status. But when Muller and colleagues looked at within group testosterone levels in association with having their children close by, interesting differences emerged. When their children were around, Hadza men were much more engaged with them compared to Datoga men who do not pay much attention to their children. Among the Hadza testosterone levels were significantly lower when children were in their household compared to when they were not around. The presence or absence of children among the Datoga had no influence on testosterone levels 5. This suggests that paternal engagement is important to any changes in testosterone. Caring and engagement makes a difference.
What does it mean to be a good father?
While human males are unique in their potential to be doting fathers, they also exhibit a much broader spectrum of paternal behaviors compared to other primates and mammals. Men can be extremely caring to simply providing food to being infanticidal. As a boy growing up in the Watts area of south central Los Angeles in the ‘60’s and 70’s, my friends and I listened to a lot of The Temptations. Among their hits was “Papa Was a Rolling Stone”, a song that tells the story of children asking their mother about their estranged, wandering father. “Papa was never much on thinkin’, spent much of his time chasing women and drinkin’…” Why some men choose the caring route while others do not is unclear. Evolutionary theory suggests that in environments with lots of hazards and a low probability of living a long life, caring for offspring may take a backseat to more risky reproductive strategies such as seeking out additional mates in lieu of investing in family. This is true of both men and women 6. Since humans have evolved the ability to thrive in a broad range of ecological and social settings, it makes sense that behavioral biology of fatherhood would be broad and malleable7,8.
Let’s go back to the question of gay dads. There is no reason to assume that caring for children should be limited to straight men but adding the variable of sexual orientation is an interesting question given the range of variability in reproductive behavior in humans. Researchers examined brain scans of gay men in association with interactions with their children. They found that areas of the brain that are commonly activated in mothers and heterosexual fathers in response to children were also evident in gay fathers suggesting that the neurobiological mechanisms associated with childcare transcend gender or sexual orientation 9. Compared to other mammals and certainly other great apes, humans seem to be biologically predisposed to care for children. Do gay fathers exhibit the same hormonal changes as heterosexual dads? We don’t know yet although Yale anthropology Ph.D. candidate Erin Burke, Dr. Pasquale Patrizio of Yale Medical School and I are hot on the trail of this question 10. There are many ways to be a dad and we’re only beginning to understand that fatherhood is as varied as the colors and patterns on a homemade necktie.
Richard G. Bribiescas is professor of anthropology and ecology and evolutionary biology at Yale University, where he also serves as deputy provost for faculty development and diversity. He is the author of Men: Evolutionary and Life History. He lives in Hamden, Connecticut.
References and Endnotes
1 Fernandez-Duque, E., Valeggia, C. R. & Mendoza, S. P. The biology of paternal care in human and nonhuman primates. Annual Review of Anthropology 38, 115–130, doi:10.1146/annurev-anthro-091908-164334 (2009).
2 Anderson, K. G. How well does paternity confidence match actual paternity? Evidence from worldwide nonpaternity rates. Curr Anthropol 47, 513-520, doi:Doi 10.1086/504167 (2006).
3 Gray, P. B. & Anderson, K. G. Fatherhood : evolution and human paternal behavior. (Harvard University Press, 2010).
4 Gettler, L. T., McDade, T. W., Feranil, A. B. & Kuzawa, C. W. Longitudinal evidence that fatherhood decreases testosterone in human males. Proc Natl Acad Sci U S A 108, 16194-16199, doi:10.1073/pnas.1105403108 (2011).
5 Muller, M. N., Marlow, F. W., Bugumba, R. & Ellison, P. T. Testosterone and paternal care in East African foragers and pastoralists. Proceedings of the Royal Society, Biological Sciences 276, 347-354 (2009).
6 Quinlan, R. J. Human parental effort and environmental risk. Proc Biol Sci 274, 121-125, doi:10.1098/rspb.2006.3690 (2007).
7 Bribiescas, R. G. Men: Evolutionary and Life History. (Harvard University Press, 2006).
8 Bribiescas, R. G. How Men Age: What Evolution Reveals about Male Health and Mortality. (Princeton University Press, 2016).
9 Abraham, E. et al. Father’s brain is sensitive to childcare experiences. Proc Natl Acad Sci U S A 111, 9792-9797, doi:10.1073/pnas.1402569111 (2014).
10 Burke, E. E. & Bribiescas, R. G. Hormones and behavior in same-sex male parents: implications for the evolution of paternal care in humans. Am J Phys Anthropol 159, 105 (2016).