Love at First Sight Might Be Genetic

Love at first sight could be real, at least when it comes to genetics, a new study suggests.

In research done with fruit flies (but which may have implications for humans) scientists found that females are biologically primed to sense which males are more genetically compatible with them, and to make more eggs after mating with good matches than they do with less compatible matches. The findings suggest that females can somehow judge a potential mate upon first meeting and biologically react to boost the chances of producing successful offspring.

The researchers mated female fruit flies with males from the same strain, and from a different strain, and noted differences in reproductive attributes and behavior soon after mating. When females mated with males that were not of the same strain, they seemed to be able to tell that they were more genetically compatible, perhaps because their progeny would be less inbred, and produced more eggs and more offspring.

It appears the females can sense which males are closely related to them — a factor that can lead to genetic defects — and respond better to males that are expected to produce healthier offspring.

"You could call it love at first encounter. That might be the most accurate, because we don’t really know what about this encounter is driving this response," said study co-author Andrew Clark of Cornell University, explaining that it wasn't just sight, but perhaps smell or sound or some other sense that alerted a female her biological match was near.

The scientists discovered that the females seemed to be in a primed state even before meeting the males, with the chemicals and proteins needed for their response already in place, without the need for new genes to be activated, as the researchers expected.

"The idea of priming is that even when the female is in the absence of males, that's her way, her status is this configuration of proteins," Clark told LiveScience. "She's wired for love. That’s who she is. And then the response to different males might be different because of that primed state."

The researchers say that the mating practices of fruit flies and humans are different enough that it's tough to directly extend their findings to humans, though it's possible that human females can also sense which males are genetically best suited to them, and their bodies may respond in ways that boost the chances of mating success.

"In mammals, including humans, the answer seems to be 'yes,' there is some differential pregnancy success deepening on the female's sensing of the male, and as a result of the genetic quality of males," Clark said.

He described a famous T-shirt experiment in humans, in which people tended to prefer the scent of T-shirts belonging to individuals that were a greater genetic mismatch for them, again perhaps the body's way of trying to prevent inbreeding.

"We also saw that males from one fly strain were more successful in garnering progeny with females [of both strains]," said study lead author Mariana Wolfner, professor of developmental biology at Cornell. "One could imagine that sort of thing happening in any species, if a particular male made more sperm, or sperm that were better at reaching or fertilizing eggs, or if he made versions of seminal proteins that better interacted with the physiology of his mate. But I don't know of any direct evidence of this in humans."

The study was detailed in the April 2009 issue of the journal GENETICS.

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