Testosterone is widely thought to increase sexual desire and aggression in men — but a new study shows it has a cozy side, too.
In experiments, researchers injected male gerbils with testosterone to see how they would behave towards their partners.
The injections encouraged cuddling and “friendly behaviors” and prepared them for “positive social interactions,” they found.
Testosterone affects the activity of oxytocin — the so-called “cuddle” or “love” hormone associated with social bonding, the researchers say, although they don’t know how.
Testosterone affects the activity of oxytocin — the so-called “cuddle” or “bonding” hormone associated with social bonding (file photo)
WHAT IS TESTOSTERONE?
Testosterone is the male sex hormone and is mainly produced in the testicles, but also in the adrenal glands, which are located near the kidneys.
It causes the voice to deepen, body hair to grow, and genitals to enlarge during puberty.
Not only does it affect sex drive and sperm production, but it also plays a role in the development of strong bones and muscles and how the body distributes fat.
Women also produce small amounts of the hormone in the ovaries and adrenal glands, and it affects their fertility, bones, and muscles.
In women, relatively small amounts of testosterone are released into the bloodstream by the ovaries and adrenal glands.
Testosterone and other androgens “play important roles in healthy female sexual function, particularly in stimulating sexual interest and maintaining desire,” according to a study published last year.
“Testosterone initiates sexual activity and increases sexual desire and behavior,” it says.
“In addition, testosterone is essential for modulating clitoral and vaginal physiology to facilitate genital lubrication, sensation, and engorgement.”
The new study was conducted by researchers at Emory University in Atlanta, Georgia, led by Aubrey Kelly, an assistant professor of psychology, and her husband, Richmond Thompson, a neuroscientist.
“We believe we have shown for the first time that testosterone can directly promote non-sexual, prosocial behavior in the same individual as well as aggression,” she said.
“This is surprising because we normally think of testosterone as an increase in sexual behavior and aggression.
“But we have shown that it can have more nuanced effects depending on the social context.”
The study, published in Proceedings of the Royal Society B, involved experiments on Mongolian gerbils (Meriones unguiculatus).
Used in scientific experiments since the 19th century, these small rodents form long-lasting pair bonds and raise their young together.
Males can become aggressive during mating and territorial defence, but they also exhibit cuddling behaviors after a female has become pregnant and they show protective behaviors towards their pups.
In one experiment, a male gerbil was introduced to a female gerbil. After forming a pair and the female became pregnant, the males showed the usual cuddling with their partners.
The researchers then gave the male subjects a testosterone injection, thinking the boost would decrease his snuggling behavior.
“Instead, we were surprised that a male gerbil became even more cuddly and prosocial with his mate,” Kelly said.
“He became such a great partner.”
In a follow-up experiment, the researchers removed the females from the cages, leaving each male gerbil that had previously received a testosterone injection was alone.
An unidentified man was then introduced into the cage – inviting the possibility of the two rivals beginning a fight.
“Typically, a male would chase or try to avoid another male that came into his cage,” Kelly said.
“Instead, the resident males, who had previously been injected with testosterone, were friendlier to the intruder.”
Mongolian gerbils (Meriones unguiculatus, pictured) have been used in scientific experiments since the 19th century
MEN WITH HIGH TESTOSTERONE ‘ARE MORE SELFISH’
High testosterone levels can make men less generous and more likely to engage in selfish behaviors, a study found.
Psychologists from China and Switzerland measured men’s brain activity while solving a task of choosing between generous and selfish options.
Men who were given supplemental testosterone three hours before completing the task tended to choose the more selfish options, they found.
Testosterone also dampened activity in a region of the brain known to be involved with regard to other people’s well-being.
However, the friendly demeanor changed abruptly when the original male subjects were given another testosterone injection.
Due to the extra injection, the male began chasing or completely avoiding the rival male invader.
“It was like they suddenly woke up and realized that they weren’t supposed to be friendly in this context,” Kelly said.
Kelly said that testosterone “enhances context-appropriate behavior” and may play a role in “enhancing the tendency to be cuddly and protective or aggressive.”
In the wild, testosterone also appears to help animals switch rapidly between prosocial and antisocial responses, depending on the context.
The researchers found that men who received testosterone injections showed more oxytocin activity in their brain during interactions with a partner than men who did not receive the injections.
Testosterone likely affects the activity of oxytocin, but researchers don’t know exactly how.
“We know that oxytocin and testosterone systems overlap in the brain, but we don’t really understand why,” Kelly said.
“Taken together, our results suggest that one of the reasons for this overlap might be that they can work together to promote prosocial behavior.”
The obvious limitation of the study is that gerbils were used instead of humans, so the results should be extrapolated to other animals with caution.
Human behavior is far more complex than that of gerbils, but the results could provide a basis for studies in other species, including humans.
“Our hormones are the same, and the parts of the brain they affect are even the same,” Thompson said.
3D representation of a testosterone molecule. Testosterone is the male sex hormone and is mainly produced in the testicles, but also in the adrenal glands, which are located near the kidneys
Previous studies have linked the presence of testosterone to various social or psychological behaviors in men.
Last year, researchers at the University of Bristol found that testosterone does not drive success in life, contradicting previous beliefs.
The Bristol experts suggested that high testosterone levels may be a result of success rather than the other way around, which may explain previous studies linking high testosterone levels to successful living.
Another 2021 study found that high testosterone levels can make men less generous and more likely to engage in selfish behaviors.