A study from earlier this year reported on the effects of 16 dogs in Japan being given intranasal oxytocin or placebo sprays. Under the influence of oxytocin, dogs socially oriented more toward their human companions and fellow dog companions. Inspired by that experiment, I recently sprayed oxytocin or placebo up the nostrils of fathers watching their children play sports. Then I sprayed oxytocin or placebo up the noses of other fathers waiting for a child to emerge from a painful surgery. Even more, I sprayed oxytocin or placebo up the noses of fathers during a children's reading time at the local library.
OK. So I made part of this story up--the part about my spraying oxytocin or placebo up fathers' noses. There are actually a couple of studies that have done just this, however. The first--from the Netherlands--found that fathers stimulated their children’s exploratory play behavior more when the fathers received oxytocin compared with placebo.
Whether you stick your nose up at the idea of hormones being blown up it, this is an exciting means by which to try gaining new insights into the role of hormones in human fathers. Here, I draw upon a new review paper by Lee Gettler, just published in "Evolutionary Anthropology," for some current thoughts on this endeavor. He discusses data on the hormones testosterone, prolactin, oxytocin and vasopressin, drawing out key concepts in evolutionary history, plasticity, social behavior, and adaptation.
A handful of recent studies on oxytocin and parenting have been published by Ruth Feldman and colleagues in Israel. They have measured oxytocin levels in blood, saliva and urine. They found that "fathers with higher baseline [oxytocin] engaged in greater stimulatory physical play behaviors with their children, while men performing more tactile exploratory play with their infants showed larger short-term (~15 min) [oxytocin] spikes than did other fathers." (p. 4) In longitudinal analysis of fathers' (and mothers') blood oxytocin, men's oxytocin was correlated across time points and with a partner's oxytocin levels, even as men's oxytocin levels also increased in the months after having a baby.
Yet the interpretation of "peripheral" peptide hormone levels (e.g., from blood, saliva or urine) is tricky for several reasons, including that oxytocin in the blood cannot cross the blood-brain barrier to exert effects on the brain. This is a major reason why intranasal peptide sprays have been so exciting--they may be exerting effects directly on the brain.
Even in the dog study (yes, that one was true), dogs given a high dose of intranasal oxytocin subsequently had measurable levels of oxytocin in their blood, suggesting that the administration of oxytocin had central effects that could be measured in the periphery. If this all sounds confusing, it shows how packaged the methods issues are in the research on hormones and fatherhood.
In the past few years, researchers have collected bodily fluids from olive baboons, gibbons and siamangs, measuring testosterone levels in males in these species. Baboon males had lower testosterone levels after forming a "friendship" with a female. "[C]aptive siamang fathers experienced a significant decline in [testosterone] over the course of their offsprings' infancy, coinciding with stark increases in father-offspring interaction." (p. 8) However, in the wild, fecal testosterone levels of male gibbons were higher in male-female pairs than male-male groups or in groups with a dependent infant. These examples suggest that male testosterone levels may be attuned to social variables—particularly a mate and offspring—in captivity and the wild.
Yet these nonhuman primate examples pose several interesting conceptual questions. Are differences in male testosterone levels (e.g. in baboons) reflective of natural selection, yielding a physiological system designed to operate in this way? Or might these differences be physiological 'noise,' plasticity without a previous selective lead-up?
Suppose you were the almighty biological craftsperson. What physiological nuts and bolts might you pull from your physiological toolkit to help serve as mechanisms facilitating human paternal care? Based on research in other animals, including some fish, birds, and mammals, you might draw upon the multifaceted potential of prolactin to help regulate features of direct childcare. This could yield some convergences in the physiological underpinnings of paternal care in different lineages of primates (including the human primate).
By now, you might think, "Hey, this is all some pretty interesting stuff about hormones and fatherhood." There are new questions about methods, data, and concepts to keep a researcher up late at night (or at least up while writing a review paper). But if you are a new father, like Dr. Gettler (congratulations, but without the cigar), you also find out in very personal ways how a baby can tug on a father's physiological strings.
Gettler, L. T. (2014). Applying socioendocrinology to evolutionary models: Fatherhood and physiology. Evolutionary Anthropology, 23, 146-160.
Naber, F., van Ijzendoorn, M. H., Deschamps, P., van Engeland, H., & Bakermans-Kranenburg, M. J. (2010). Intranasal oxytocin increases fathers’ observed responsiveness during play with their children: a double-blind within-subject experiment. Psychoneuroendocrinology, 35, 1583-1586.
Romero, T., Nagesawa, M., Mogi, K., Hasegawa, T., & Kikusui, T. (2014). Oxytocin promotes social bonding in dogs. Proceedings of the National Academy of Sciences, 111, 9085-9090.