Testosterone administration decreases generosity in the ultimatum game

Abstract

How do human beings decide when to be selfish or selfless? In this study, we gave testosterone to 25 men to establish its impact on prosocial behaviors in a double-blind within-subjects design. We also confirmed participants' testosterone levels before and after treatment through blood draws. Using the Ultimatum Game from behavioral economics, we find that men with artificially raised T, compared to themselves on placebo, were 27% less generous towards strangers with money they controlled (95% CI placebo: (1.70, 2.72); 95% CI T: (.98, 2.30)). This effect scales with a man's level of total-, free-, and dihydro-testosterone (DHT). Men in the lowest decile of DHT were 560% more generous than men in the highest decile of DHT. We also found that men with elevated testosterone were more likely to use their own money punish those who were ungenerous toward them. Our results continue to hold after controlling for altruism. We conclude that elevated testosterone causes men to behave antisocially.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1. In the Ultimatum Game, Decision-Maker 1 (DM1) is endowed with $10 and DM2 has no endowment.

DM1 proposes a split of his endowment to DM2 that DM2 can either accept or reject. Accepted proposals are paid to both DMs while rejected proposals cause both DMs to receive nothing. All participants made proposals as DM1s and as DM2s were asked to state their minimum acceptable proposal to elicit their punishment thresholds. After making decisions as DM1 and DM2, the roles were randomized to determine earnings. Both DMs were fully and identically instructed in this task. The subgame perfect equilibrium is for DM1 to offer $1 and for DM2 to accept this.

Figure 2. Values of total T, free T, and DHT before and after Androgel® treatment; all differences p

The blue bar is basal T and the blue plus the red bar is the post-treatment T value (and SE bars). T in every treated subject was higher than baseline. The highest level of total T after treatment was 10.32 pg/ml or a 170% change from baseline; the smallest change in total T was 0.31 pg/ml or a 7% change.

Figure 3. Generosity (UG offer - UG punishment threshold) by participants on placebo was $2.15 compared to $1.57 when the same individuals were given Androgel®, a 27% reduction (p = .035; bars in graph are SEs).

More participants on Androgel® relative to placebo showed negative generosity by setting a punishment threshold above than their own offer to DM2 (9.6% vs. 2.9%).

Figure 4. Scale effect of T on generosity.

T levels and generosity for those on placebo are shown in blue, generosity for those on Androgel® are shown in red. (A) The reduction of generosity for those on Androgel® positively scales with levels of total T, free T and DHT; the relationship for DHT is shown (r = −0.3063, p = 0.0001). Men in the lowest decile of DHT had average generosity of $3.65 compared to generosity of $0.55 for men in the highest decile of DHT (85% lower). (B) The punishment threshold also scales with a man's level of total T, free T and DHT; the relationship for DHT is shown (r = 0.2284, p = 0.0011). Men in the lowest decile of DHT had average punishment threshold of $2.15 compared to a punishment threshold of $4.00 for men in the top decile of DHT (86% higher).