“In low narcissists, testosterone was linked to less prosocial behavior,” Ziemiańska told PsyPost. But “in high narcissists, testosterone was linked to more prosocial choices.”

“Altogether, the pattern of results was a bit counterintuitive,” she said. “The two different factors i.e. psychological trait narcissism and the level of hormone testosterone influenced social behavior in a rather unexpected fashion. As mentioned before, popular beliefs are that high testosterone levels, as well as high narcissism, are linked to competitive, antisocial behavior (even explicit aggression).”

“This is why we were surprised to discover that, contrary to these popular beliefs, endogenous testosterone was associated with lower generosity among less narcissistic — thus more trustful, less cynical, more habitually generous, and less selfish — men,” Ziemiańska explained.

The findings might also have some practical implications.

“One (perhaps somewhat funny) takeaway message from our study would be: if you are choosing a date, beware of highly narcissistic men who are simultaneously low on baseline testosterone – in our studies, they were the least generous (and most selfish) in their decisions,” Czarna added. “They shared the least resources with others. So, when going on a date with one of them – prepare to pick up the bill. Meanwhile, men who were low on both narcissism and testosterone were highly generous.”