The majority of human studies show that testosterone enhances aggressive behavior. Kelly and Thompson wondered whether testosterone might, in a stepping stone with the potential to increase aggression toward intruders, also often reduce social behaviors.
However, they also theorized that it might do something more radical, actually enhancing positive social response in contexts where pro-social action is appropriate.
To test this question, they conducted experiments on Mongolian gerbils, rodents that form strong pair bonds and raise their pups together. Although males can become aggressive during mating and defending their territory, they also exhibit cuddling behavior after the female becomes pregnant and they display protective behavior towards their offspring. .
In one experiment, a male gerbil was introduced to a female gerbil. After they form a pair bond and the female becomes pregnant, the male displays the usual cuddling behaviors towards his mates.
Testosterone makes you a lovely partner
The researchers then injected testosterone into the male subjects. They hope that a rapid rise in a man’s testosterone levels will dampen his cuddling behaviors if testosterone in general acts as an antisocial molecule.
Instead, they were surprised that a male gerbil was even more cuddly and friendly with his mates. In a follow-up test a week later, they conducted a check on the resident intruders.
The females were removed from the cage so that each male gerbil had previously been injected with testosterone alone in its home cage. An unidentified male was then brought into the cage.
Usually, a male will chase another male that has entered his cage or try to avoid it. Instead, resident males that have been previously injected with testosterone are more intruder-friendly.
However, friendly behavior abruptly changed when the male subjects were initially injected with another dose of testosterone. They then began exhibiting the usual chase and/or avoidance behaviors to the intruder.
The researchers hypothesized that because male subjects experienced an increase in testosterone when they were with their partner, it not only rapidly increased positive social responses to them, but also provide opportunities for men to act more socially in the future, even when the context changes and they involve another man.
However, a second injection of testosterone soon followed, causing them to switch their behavior to become more aggressive, befitting the context of a male intruder. It seems that testosterone enhances contextual behavior.
Testosterone finely regulates behavior
Laboratory experiments, in a sense, slow down what males can experience almost simultaneously in the wild. In their natural habitat, mating with a mate increases testosterone, which enables them to act affectionately in the moment and in the near future when cohabiting, even as testosterone levels drop. .
If an opponent steps into its den, the gerbil will likely experience another surge of testosterone immediately that helps to adjust its behavior so it can fend off the opponent and protect its pups. Then, testosterone seems to help animals swing rapidly between social and antisocial responses as the social world changes.
The current study also looked at how testosterone and oxytocin interact biologically. The results showed that the male subjects injected with testosterone had more oxytocin activity in their brains during their interactions with their sexual partners than the men who did not receive the injection.
Taken together, the study results suggest that one of the reasons for this overlap may be that they can work together to promote pro-social behaviour.
Instead of just turning an “on” or “off” button to regulate behavior, hormones seem to play a more nuanced role. It’s like a complicated panel where one dial may need to move up a bit while another moves down.
Human behaviors are much more complex than those of the Mongolian gerbil, but the researchers hope that their findings provide the basis for additional studies of other species, including humans.