If dad was a playboy, there's a good chance that his sons and daughters will also be promiscuous, suggests a new study that identified a genetic link to such behavior.
Moral objections aside, promiscuity can benefit a species because it often results in more progeny with greater genetic diversity. There are clear risks, such as having a higher chance of acquiring a sexually transmitted disease, but the genetic predisposition to play the field appears to be locked into the DNA of socially monogamous species, including humans.
"Other research has concluded that sons of promiscuous fathers are two times more likely to cheat than others," lead author Wolfgang Forstmeier told Discovery News, adding that daughters of such fathers and mothers would also be more likely to cheat.
Forstmeier, a researcher in the Department of Behavioural Ecology and Evolutionary Genetics at the Max Planck Institute for Ornithology, and his colleagues wondered about the genetic connection after conducting studies, such as behavioral surveys, on humans.
For this paper, published in the latest Proceedings of the National Academy of Sciences, they decided to investigate the phenomenon among zebra finches, which are also socially monogamous.
"That means a male and a female will hang out together as a couple; they will build nests together and share other forms of bonding," Forstmeier said. "They may also, however, engage in extra-pair mating behavior."
In other words, like humans do from time to time, they may cheat on their primary mates.
For the study, the scientists studied the behavior of 1,554 zebra finches from five consecutive generations. During one experiment, the researchers analyzed the DNA of some adult bird parents.
The scientists then took the eggs of those parents and placed them in the nests of other individuals. Fostering of unrelated offspring occurs naturally among these birds, but only about 15 percent of the time.
The scientists next analyzed the DNA of the offspring, comparing each young bird's genetic profile with that of the adults. The genetic analysis not only indicated birth family connections, but there was also a strong noticeable genetic correlation between both male and female measurements of extra-pair mating behavior.
The birds could not have learned this behavior from their randy parents, since foster parents raised them. They must have inherited a tendency for it.
"The study provides a good explanation for what we see in humans," Forstmeier said. "Statistics have shown that promiscuous parents are more likely to sire sons and daughters with a greater tendency to cheat."
He is quick to add, however, that promiscuity is a complex trait involving many other factors.
"Even if a person has such an internal desire, the outcome may depend on that individual's attractiveness," he explained. "Also, differences in extroversion exist, meaning that some people may be more inclined or not to act on their feelings."
Personal experiences, education, and other more environmental influences could also help to shape the person.
It remains unclear precisely how genes may predispose an individual to play the field, but hormones must be involved. Interestingly enough, testosterone, primarily thought of as a male hormone, appears to help drive the female sexual libido, so that connection could be key.
For years, researchers have wondered why females would cheat on their mates, given that there appears to be no direct benefit, but it could be that they retain the genes in order to pass them down to their sons, or just harbor them because the trait is positively selected for in males. DNA associated with large body size and risk-taking may persist in genomes for similar reasons, Forstmeier said.
David Westneat, a University of Kentucky biologist, told Discovery News that he thinks "this is an excellent and thorough study producing some thought-provoking results. The authors did an excellent job with their methods and with appropriately interpreting their results."
"Applying this result to humans is both thought-provoking and dangerous," Westneat continued, adding that "there are many reasons to think that human behavior is influenced by many other factors. But, he concluded, the new "study does make one consider the possibility with more seriousness than before."