Marital status and paternal responsibility may have a significant effect on levels of testosterone and other hormones in men, according to two new studies published this fall by a researcher at the University of Nevada, Las Vegas (UNLV).
The studies, conducted by UNLV anthropology professor Peter Gray, are among the first of their kind conducted outside North America to show that hormone levels differ significantly not only between fathers and non-fathers, but also between single men and men involved in long-term marital relationships. These kinds of novel research on hormones and human partnering represent an exciting new advance in the field and represent one of the frontiers of human biology and behavior.
“As the scientific community begins to understand more about the biology of man, the better able we are to examine other psychological and behavioral outcomes, including the elevated risk of postpartum depression among men and the potential negative effects of testosterone supplementation on paternal investment and care,” says Gray.
Gray and his colleagues sought to expand the body of research - most of which was done in North America - by looking at others regions around the world for a cross-cultural perspective. Over the past three years, Gray conducted studies in East Africa and Jamaica.
In the east African study, published in the October issue of the journal “Current Anthropology,” Gray and fellow researchers, Ben Campbell of the University of Wisconsin, Milwaukee, and Peter Ellison of Harvard University, examined the effect of marital status on testosterone. They conducted their research among the Ariaal pastoralists in Northern Kenya, comparing testosterone levels between single men, men married to one wife, and men married to multiple wives. The team examined saliva samples from 205 men over 20 years of age.
The results showed that, similar to North American men, monogamously married Ariaal men had significantly lower morning and afternoon testosterone levels compared to their single counterparts of similar age (20-39). Surprisingly, older polygynous Ariaal men had lower testosterone levels than their monogamous counterparts. These latter findings suggest that, among older men, the decrease in testosterone doesn’t stop with one wife and that social status and wealth - rather than testosterone-related behaviors - may better determine whether a man had more than one wife.
The second study, published in the November issue of the journal “Hormones and Behavior,” was conducted in Jamaica with Maureen Samms-Vaughan of the University of the West Indies and UNLV graduate student Jeff Parkin. In this study, Gray and his team examined the effect of human fatherhood on the hormones testosterone, prolactin, oxytocin, cortisol and vasopressin.
Hormone concentrations were analyzed from 43 Jamaican men aged 18-40 who fell into one of three relationship groups:
- biological fathers engaged in visiting relationships
- biological fathers living with their youngest child
The results showed that testosterone levels were significantly lower in visiting Jamaican fathers than in single Jamaican men. This suggests that the correlation between testosterone and fatherhood, first observed in Canada, may apply more broadly.
It was also found that prolactin levels of single men declined significantly compared with flat levels of visiting fathers who participated in a 20 minute session with their children. These changes in prolactin levels suggest that the stimulation of dads interacting with kids may elevate prolactin levels. Among the fathers, vasopressin levels were significantly and negatively correlated with the age of a man’s youngest child.
The research was funded, in part, through support from the Wenner-Gren Foundation and the Yale Center for Human and Primate Reproductive Ecology, respectively.
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