Researchers have taken a healthy stride towards understanding the evolutionary role of the nice guy.

A recent study of water striders—insects found skimming the surfaces of ponds and streams around the world—showed that while aggressive males enjoy greater reproductive success as individuals, more gentlemanly striders gain an unexpected advantage in the bigger picture.

The problem for aggressive males is that female water striders quickly tire of their harassment and skate away to regions inhabited by more laid back individuals. “The key result is that this really affects the success of the males,” says Stuart Wigby, an evolutionary biologist at Oxford. With more females around, the laid back males have a greater shot at reproducing.

“Nice guys don’t always finish last,” says Omar Eldakar, the study’s principle investigator.

Prior to this research, it was unclear how non-aggressive males fit into evolutionary competition. But Eldakar recognized a link between this problem and “the tragedy of the commons,” a trend that normally applies to overexploitation of natural resources. “If there are individuals that are sharing a common resource, then selection is going to favor a short term exploitative strategy,” he explains. “Eventually the resource is destroyed.”

In the Grand Banks cod fishery, for instance, a fishing vessel did well for itself by catching all the fish it could, but in time this behavior caused a collapse in cod populations, devastating the entire industry.

In water strider reproduction, the shared resource is females, and competition between aggressive males can result in overexploitation. Eldakar established this link in a paper published earlier this year. In a lab at Binghamton University, he measured the aggressiveness of 144 male aquarius remigis based on the number of times they lunged at, jumped on, or otherwise tried to mate with their fellow water striders.

He then put his striders into four separate pools, six females and six males to a pool, with zero, two, four and six of the most aggressive males respectively in the four groups. The remaining males in each pool were selected from among the mellower individuals of the study.

In the mixed pools of aggressive and non-aggressive males, Eldakar saw that the pushier individuals were three and seven times more successful in mating. But as the proportion of aggressive males in a pool increased, total copulation plummeted—the pool with all aggressive males experienced less than a third of the number of matings that took place in the tank with only two pushy striders. The reason for this lay in the females.

When they are harassed, female water striders become less fit for reproduction. They waste precious energy confronting their suitors, struggling to throw the males off their backs. If they can’t, they’ll have to lug them around for as long as twelve hours. “Once they’ve been pounced on a few times,” says John Pepper, a co-author on Eldakar’s most recent study, “they decide this is not a good place for them to be.”

Since water striders sense much of their environment through ripples in surface tension, the females in these tests would leave the water’s surface to escape male detection, even though this meant they couldn’t hunt or feed. In the rowdy pool of aggressive males, they spent only thirty-six percent of their time on the water’s surface, compared to ninety percent in the calmer pool of non-aggressives.

To test how this tragedy of the commons might affect a real population of dynamic groups, Eldakar set up a similar experiment, but this time he allowed the water striders to move freely between pools, as they might on a natural stream.

The result, reported in the November 6 issue of Science, was that females and non-aggressive males avoided the pushy males, lending a reproductive advantage to the gentler individuals that clustered together. “[This] shows that differences in reproductive success between groups really do impact evolutionary outcomes,” says Pepper.

Eldakar points out that his research contradicts naive notions of survival of the fittest, at least when fittest means biggest, strongest, fiercest, or most brutal. “Evolution isn’t such a bad thing,” he says. It can explain everything from cooperation in honey bees to human morality.