Most human studies suggest that testosterone increases aggressive behavior. Kelly and Thompson thought that perhaps testosterone may have been in lockstep with being able to increase aggression toward intruders, usually also reducing prosocial behavior.
However, he also hypothesized that it may do something more radical, actually increase positive social responses in contexts in which acting socially is appropriate.
To test this question, they conducted experiments on Mongolian gerbils, rodents that form permanent pair bonds and raise their pups together. While males can be aggressive during mating and defending their territory, they also display cuddling behavior after the female becomes pregnant, and they display protective behavior towards their pups.
In one experiment, a male gerbil was introduced to a female gerbil. When they formed a pair bond and the female became pregnant, the males displayed normal cuddling behavior towards their partners.
Testosterone makes you a loving partner
The researchers then gave male subjects an injection of testosterone. They hoped that if testosterone normally acts as an antisocial molecule, the resulting rapid increase in a male’s testosterone level would reduce his cuddling behavior.
Instead, they were surprised that a male gerbil became even more paranoid and prosocial with his mate. In a follow-up experiment a week later, they performed a resident-intruder test.
Females were removed from the cages so that each male gerbil that had previously received a testosterone injection was alone in its home cage. Then an unknown male was introduced into the cage.
Normally, a male chases another male who comes into his cage or tries to escape from him. Instead, resident males who had previously been injected with testosterone were more friendly towards the intruder.
The friendly behavior suddenly changed, however, when the original male subjects were given another injection of testosterone. They then began to display normal stalking and/or avoidance behavior with the intruder.
The researchers believe that because male subjects experienced an increase in testosterone while they were with their partners, this not only led to a rapid increase in positive social responses towards them but also caused men to become more socially inclined in the future. motivated to act, even if the context has changed and they were in the presence of another man.
However, the second testosterone injection caused them to rapidly change their behavior, as is appropriate in the context of a male intruder. It appears that testosterone enhances context-appropriate behavior.
Testosterone controls behavior in a delicate way
Laboratory experiments have, in a sense, slowed the experience of males almost simultaneously in the wild. In their natural habitat, mating with a partner increases testosterone, which prompts them to act cuddly in the moment and near future while being with their partner, even when testosterone levels drop.
If a rival enters his burrow the gerbil will experience another surge of testosterone which will immediately help him adjust his behavior so that he can deter the rival and protect his pups. Testosterone then appears to help animals rapidly pivot between prosocial and antisocial responses as the social world changes.
The current study also looked at how testosterone and oxytocin interact biologically. The results showed that male subjects who received injections of testosterone demonstrated greater oxytocin activity in their brains during interactions with a partner than men who did not receive injections.
Taken together, the study results suggest that one of the reasons for this overlap may be that they may work together to promote prosocial behavior.
Rather than simply flipping an “on” or “off” button to modulate behavior, hormones play a more subtle role. It’s like a complicated dashboard where one dial may need to move up a bit while the other down.
Human behaviors are far more complex than those of Mongolian gerbils, but the researchers hope their findings provide a basis for complementary studies on other species, including humans.