According to research appearing in the Proceedings of the National Academy of Sciences, sexual promiscuity by married men--and women--is built into the DNA of socially monogamous species such as humans.
Jennifer Viegas, writing in Discovery News, calls it the "Playboy gene." If dad was a player, then there's a good chance that his sons and daughters are, too. And while this behavior might be traumatic for individual families, the species as a whole benefits from more progeny with greater genetic diversity, Viegas writes. "Other research has concluded that sons of promiscuous fathers are two times more likely to cheat than others," lead author Wolfgang Forstmeier told the news outlet, adding that the same is true for daughters.
How do they know this? By observing zebra finches. They took the "nurture" part out of the equation by placing eggs into the nests of unrelated foster-parent birds. And, of course, it turned out that if the genetic parents showed "extra-pair mating behavior," so did the offspring. They could not have learned it from their natural parents, since they were raised by foster parents. "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, though, that zebra finches are not humans, who may have the "internal desire" to cheat, but are not inclined to act on those feelings.