From the article:
To test this hypothesis, the researchers had 54 female volunteers ingest a liquid solution several hours before participating in an investing game – some volunteers received a placebo solution, while others received a solution with added testosterone.
In the investing game, participants were given €20 (about $27 USD) and were instructed that they could keep the amount they wanted and invest whatever remained with a trustee (another participant). The invested portion would be tripled and split by the trustee, who would keep whatever portion she wanted and return the rest to the investor.
If participants were completely trusting, they could invest all €20 and hope that the trustee would split the final €60 equally. If they wanted to play it safe, they could keep the €20 for themselves.
Each participant took turns playing both investor and trustee. When they were the trustee, they were always given €60, indicating that the investor had entrusted them with the task of splitting up the whole sum.
As investors, participants who received testosterone were, on average, stingier – they placed less trust in the trustee and kept more of their initial money. Participants who received the placebo, on the other hand, were more trusting investors, choosing to invest about €3.20 more than those who received testosterone.
Just as the researchers predicted, testosterone seemed to promote antisocial behavior in response to a potential threat – in this case, a threat to financial resources.
But the opposite effect emerged when participants played the role of trustee. In this case, participants given testosterone chose to give more money back to the investor than participants who had been given a placebo. The results suggest that the trustees felt a responsibility to repay the trust that the investor ostensibly placed in them.
“While we expected the decrease in trust found in the first scenario, the increase in reciprocity was surprisingly strong and robust,” Boksem notes. “Testosterone had a more pronounced effect on prosocial behavior than on antisocial behavior.”