12 September 2006

Dad's Smell Puts The Kibosh On Inbreeding

by Kate Melville

Researchers from Penn State's Altoona Campus say that pheromone cues from human fathers may delay the onset of sexual maturity in their daughters, as part of an evolutionary strategy to prevent inbreeding. "Biological fathers send out inhibitory chemical signals to their daughters," said researcher Robert Matchock. "In the absence of these signals, girls tend to sexually mature earlier."

In the animal world, chemical cues and their effect on sexual maturity have been recognized for some time and other researchers have noted that if the biological father is removed from rodent families, the daughter rodents tend to mature faster.

The Penn State scientists took this prior research, put it with the recent discovery of a little-known pheromone receptor gene in the human olfactory system that links the role of pheromones to the first occurrence of menstruation; and designed a new study to test for pheromone effects in human sexual maturation.

The new study, published in the American Journal of Human Biology, collected menarche data from nearly 2,000 college students to explore the link between girls' social environment and their sexual maturity. The data included information on factors such as the girls' family size, social environment, and how long the father had been absent.

"Our results indicate that girls without fathers matured approximately three months before girls whose fathers were present," Matchock explained, adding that the data seem to suggest a relationship between the length of the father's absence and the age of menarche - the earlier the absence, the earlier the menarche.

Interestingly, results from the study also suggest that the presence of half and step-brothers was linked to earlier menarche, as was living in an urban environment. The researchers speculate that urban environments provide greater opportunities to get away from parents' inhibitory pheromones, and encounter attracting pheromones from unrelated members of the opposite sex. "It is possible that a stimulating urban environment can negate suppressive cues from parents," mused Matchock.

The researchers say the study is an explanation of how pheromone cues modulate sexual maturity, to enhance mating and prevent inbreeding. "Prevention of inbreeding is so crucial to successfully spread healthy genes that anti-inbreeding strategies such as the use of pheromones seem to be conserved across species," concluded Matchock.

Source: Penn State