Scientists have long believed that women are more adept at bonding with other women, while men can be more competitive and aggressive with other men. But a new study suggests that the differences may not be as large as that.

The research, published in the journal Neuropsychopharmacology, involved experiments with rats. Rats, it turns out, are a lot like humans in their social lives. They groom each other, sleep together and have even shown empathy by helping distressed rats.

Elizabeth Kirby, a postdoc at Stanford who began the work while a doctoral student at the University of California at Berkeley, studies the effect of stress on the brain. She exposed some male rats to a mild stress — by immobilizing them in a tube for a few hours — and then put them back in a cage with each other.

The change was dramatic. They were less aggressive, hung out closer to each other and shared their water bottle more without any fighting.

Kirby explained in an interview that this is akin to male friendships or bromances in the first year of college that help students deal with stress. "You take a bunch of 18-year-old males and put them in a new place away from home, and they form really strong friendships," she said.

Next, the researchers exposed the rats to a more life-threatening stress — the odor of a predator — and other negative changes. But after those experiences, there was no bonding, and the rats began to stay away from each other.

Kirby said what happened is similar to how a human might react to being in a car wreck and have post-traumatic stress disorder and withdraw from social networks.

She said that the study should give us pause about how we think about stress.

"Stress is not universally bad. Every time we feel stressed, we don't need to be de-stressed and have negative emotions associated," Kirby said. "It can also be beneficial to psychological health."

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