98 human, male, japanese, Kyushu U students aged 20-30 took either (double-blind random assignment) minocycline pills or lactose pills for four days.
Then, during/after the interview on effects/side-effects of the pills, the interviewer “gave” them 1300 JPY and showed them a picture of a young female (of otherwise identical demographic). The male subject decided how much of the 1300 yen to “bet” by giving her, after rating how attractive she seemed and rating how trustworthy she seemed, and then if she cooperated they received 150% of this amount + 650 JPY¹, or nothing if she defected (and the woman kept what they gave her multiplied by three).² This exercise was repeated seven times, so one Game for each of the 8 pictures for each male participant.
Overall, mitocycline subjects seem to have given less money in general (at the mean), and lactose subjects seem to have given much larger fractions of 1300 JPY at the mean when they rated females more attractive—meaning that the effect is not only explained by a larger amount of males giving all the money, and may indicate that less males kept all the money.
The raw data is not available as far as I’ve found, so there’s not much to go on to verify the statistical analysis.
1: Basic math should render it obvious that if the man gives less than 217 JPY, the woman will almost certainly defect, since cooperating otherwise would leave her with less money than she started with. See point 2 below for the logic of how the game worked.
2: As the game was explained to the male participants: Each of the two players start with 1300 yen, and the man chooses how much (or nothing) to give to the woman—this amount he gives is tripled, and then the woman decides whether to keep the new total (3 the gift + 1300) or split it 50-50 (and keep 1.5 the gift + 650). It is not specified, but I believe the men were led to believe that the woman would take her decision after learning how much they (the man) decided to share with her.
TL;DR of the paper:
98 human, male, japanese, Kyushu U students aged 20-30 took either (double-blind random assignment) minocycline pills or lactose pills for four days.
Then, during/after the interview on effects/side-effects of the pills, the interviewer “gave” them 1300 JPY and showed them a picture of a young female (of otherwise identical demographic). The male subject decided how much of the 1300 yen to “bet” by giving her, after rating how attractive she seemed and rating how trustworthy she seemed, and then if she cooperated they received 150% of this amount + 650 JPY¹, or nothing if she defected (and the woman kept what they gave her multiplied by three).² This exercise was repeated seven times, so one Game for each of the 8 pictures for each male participant.
Overall, mitocycline subjects seem to have given less money in general (at the mean), and lactose subjects seem to have given much larger fractions of 1300 JPY at the mean when they rated females more attractive—meaning that the effect is not only explained by a larger amount of males giving all the money, and may indicate that less males kept all the money.
The raw data is not available as far as I’ve found, so there’s not much to go on to verify the statistical analysis.
1: Basic math should render it obvious that if the man gives less than 217 JPY, the woman will almost certainly defect, since cooperating otherwise would leave her with less money than she started with. See point 2 below for the logic of how the game worked.
2: As the game was explained to the male participants: Each of the two players start with 1300 yen, and the man chooses how much (or nothing) to give to the woman—this amount he gives is tripled, and then the woman decides whether to keep the new total (3 the gift + 1300) or split it 50-50 (and keep 1.5 the gift + 650). It is not specified, but I believe the men were led to believe that the woman would take her decision after learning how much they (the man) decided to share with her.
I wish we’d stop using lactose as a placebo.