Eau de Daddy Means Later Periods

Your dad is a man whose babies you do not want to bear. It is gross, criminal in many countries, and would be genetically ruinous for your consanguineous offspring.

What’s more, this ancient evolutionary no-no seems to have startling modern day implications for female maturation. A study of 2,000 US college girls published in the American Journal of Human Biology in July 2006 shows that daughters who grow up without their fathers tend to have their first period earlier than those who blossom under their dad’s wing. Robert Matchock, who led the retrospective survey at Pennsylvania State University Altoona, believes there is a mechanism at play here that helps prevent inbreeding.

The psychologist saw an intriguing connection between his results and previous research on human pheromones - odors used in animal communication, often to attract mates. “Biologically related males send out inhibitory pheromone signals, whilst unrelated men release stimulatory ones,” says Matchock. In other words, daddy chemically says: Don’t ripen too fast, bunny; whilst strangers exude: Bring it on!

Hence, the earlier the father leaves, the earlier his daughters reach menarche—the proper term for a girl’s first period. In this study, the presence of other non-related males, such as a half-brother or adoptive father, is also associated with an earlier sexual maturation. Besides, Matchock’s idea would explain why city chicks in his sample have an earlier menarche than country girls. “They have more opportunities to be away from their fathers and to be exposed to other stimulatory male effects,” he explains.

The phenomenon is well known and has been interpreted differently in the past. For instance, Jay Belsky’s “psychosocial acceleration theory” from 1991 posits that girls who sense high levels of family stress (such as family conflict, divorce, and father absence) mature early as a reproductive strategy. Studies on families who have experienced traumatic events do suggest that stress can hasten maturation time. But European studies of girls from war-torn countries such as Croatia also suggest that stress can delay maturity. Matchock believes it makes more sense to delay sexual maturation until a safer time, when life is more conducive to reproduction. And the stress induced by an absent father could easily be confounded through Matchock’s inbreeding avoidance mechanism.

His theory, of course, is contentious, with all the suggestive overtones for step-fathers and brothers. Matchock is therefore looking to establish a consistent link between his observations and actual physiological mechanisms. He is now planning further research with direct measures of pheromones. Despite previous studies demonstrating the effects of human pheromones, such as the regulatory effect of male armpit sweat on women’s menstrual cycle, “pheromone theories in humans no doubt receive harsh criticism,” Matchock admits. However well accepted in other mammals, the notion of chemical sexual signals is often mocked in humans. “Charlatans selling pheromone perfumes as attraction potions and the like discredited it,” he deplores.