Testosterone’s Surprising Link to Men’s ‘Love Hormone’ Oxytocin

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After Testosterone Blast of Hunting, Men’s ‘Love Hormone’ Rises When They Return Home

Testosterone. It fuels the drive of hunters, athletes, traders in the financial markets and other so-called “Alpha males.”

And regardless of their differences, they all tend to have one thing in common: they are all ultra-competitive and possess an almost superhuman drive to succeed.

As a result of this drive, their testosterone levels are off-the-charts, primarily when they are engaged in the high-level competition of their brutally Darwinist fields.

But There is Another Side to This Story

The Chinese call it Yin/Yang.

In Viking times, it was called Fire/Ice.

The ancient Greeks called it “The Golden Mean.”

Regardless of the name, the fundamental concept remains the same today: balance, including mental, physical and emotional aspects, is something that we all need, and strive for, at times unconsciously.

And it is just as relevant today as it was thousands of years ago.

Fascinating New Research

A new study explores the nurturing, familial side of men who pursue primal activities, often to support their families.

It finds that that side, too, is expressed hormonally, when a man brings dinner home to his family (or perhaps money or a trophy).

The results of the study were surprising, and a bit unexpected.

The more a man’s testosterone has risen in his choice of hardcore male activity, the more the “love hormone” oxytocin tends to surge upon coming home, researchers have found.

The researchers also discovered that the longer his workday, the higher his oxytocin levels are when he returns to his family.

Previous studies have shown that oxytocin makes people more cooperative while testosterone has the opposite effect.

That finding, which was one of the first to measure oxytocin release in a naturalistic setting, emerged after anthropologists from University of California, Santa Barbara shadowed male members of an Amerindian tribe in the Amazon Basin of Bolivia as they hunted for food.

To conduct the study, UCSB anthropologist Benjamin C. Trumble joined the hunters as they went out into the jungle and attempted to make a kill to feed their families.

The 31 men studied were members of the Tsimane hunter-gatherer tribe of Bolivia.

Trumble collected salivary samples (spit) from the hunters, first as they departed on their day long, and often solitary hunts; again after their first chance to bag a prey animal; and finally, shortly after they returned home.

The oxytocin was measured in the UCSB Human Biodemography Laboratory.

Published in the Royal Society’s Biology Letters, the resulting findings discovered (much to their surprise) that men whose “day job” drove their testosterone highest also experienced the highest levels of oxytocin when they came home.

The team also found that high testosterone levels while hunting could be attributed to a "winner effect" experienced by men making a kill.

The increased oxytocin could serve as a balance to make the hunters kinder, more generous and more willing to share their bounty.

At first glance, this does indeed seem strange.

Testosterone and oxytocin are antagonistic, said UCSB anthropologist Adrian V. Jaeggi, co-lead author: Though high levels of testosterone are usually associated with aggressive, drive-for-dominance behavior, bursts of oxytocin are linked to sharing, cooperation, trust, and tenderness.

'Our goal was to look at the interaction between different hormones in motivating behavior in a naturalistic context,' said Jaeggi.

'Hunting for subsistence and sharing meat is something people have done for hundreds of thousands of years.'

The needs of the social group may demand that a man who has demonstrated aggression all day find a way to reintegrate with his kin and share his food.

The release of the hormone oxytocin may serve precisely to help in that transition, or to signal that the returned hunter has successfully shifted roles, said Jaeggi.

“Testosterone, whatever the reason for the increase, is liable to make you more asocial, and that might not be a good thing when you’re coming home to your family and community,” Jaeggi said.

“Oxytocin, on the other hand, makes you more empathetic, which would be useful in a social context.”

Restoring Physical Balance as Well as Emotional Balance

Both hormones may play another role for returning hunters: After the physical exertions of the hunt, testosterone and oxytocin also have been shown to assist in rebuilding muscle.

That tonic effect may be purely coincidence, or it may have been the hormonal influence that helped men in early human societies form bonds with their partners and children.

"These men are coming home, they're finished with work for the day, and they're about to eat and share food," Jaeggi continued.

"So the need to be social coincides with the need to regenerate, and it would make sense for the same hormones to facilitate both functions."

Jaeggi said he expected to see a trade-off between the two hormones and was surprised to find the positive relationship between them.

As mentioned earlier, Jaeggi and co-lead author Trumble feel that high testosterone while hunting could be attributed to a 'winner effect' experienced by men making a kill.

It could also be related to the status competition that hunting represents for traditional societies such as the Tsimane.

In either case, the increased oxytocin could serve as a balance to make the hunters kinder, more generous and more willing to share their bounty.

'Almost half a century ago, it was famously documented that successful Kung hunters were jokingly insulted by others to 'cool their hearts' to 'make (them) gentle,' lest pride or boasting disrupt the egalitarian social system common to many foragers,' said senior co-author Michael Gurven.

'Here we observe a potential hormonal analog consistent with the type of leveling behavior seen in hunter-gatherer societies.'

The latest study on oxytocin is a sharp contrast to a plethora of new research on the hormone.

This study measured oxytocin in circulating blood (not in the brain, where it may do its heaviest lifting) in a natural setting. But many other studies have puffed solutions of oxytocin up the nose to see how and if an increase would affect behavior.

Both methods seem to converge on the conclusion that oxytocin has probably played an influential role in the evolution of humans’ social bonds.

Jaeggi said the finding that a lengthy absence from home was linked to higher oxytocin levels upon return suggested the notion that absence makes the heart grow fonder could be a universal human experience.

“Reconnecting with their families after a day of separation would have been a pervasive challenge for men throughout evolutionary history, and oxytocin could help with that.”

Who are the Tsimane People?

The study was based on Tsimane people, who are an indigenous population of forager-farmers and hunters who live in the lowlands of Bolivia's Amazon basin.

Researchers claim the human hormone system is particularly well adapted to their lifestyle which revolves around small, tight-knit communities.

Though the sample size is 'not enormous,' he and Jaeggi noted, the study 'definitely adds to the current literature in which the interplay between testosterone and oxytocin is often overlooked.'

There's No Place Like Home

So how can the findings among a group of indigenous hunter-gatherers in central Bolivia be applied to modern Western culture?

"I think the 'absence makes the heart grow fonder' effect could potentially be prevalent," said Jaeggi.

"Reconnecting with their families after a day of separation would have been a widespread challenge for men throughout evolutionary history, and oxytocin could help with that."

Other research on oxytocin has shown its value as a means of quantifying the depth of interpersonal relationships.

"Oxytocin levels indicate how much you value another person," said Jaeggi.

"It's a physiological measure of the value of that relationship."

For example, fall in love with someone and your oxytocin level will skyrocket whenever your sweetheart is near, both literally and figuratively.

"Even talking to someone on the phone is enough to cause that oxytocin increase," he continued.

Of course, men are not the sole beneficiaries of oxytocin's benefits.

"Like the biology of most social behaviors, it originated in the mother-infant context, where it facilitates giving birth, nursing, and bonding," Jaeggi explained.

"It is found in all mammals, and it then got used in other contexts in some species."

One finding that surprised the researchers involved the correlation of social variables to oxytocin increase: There was none.

"I would have expected that men who have more children experience a greater increase when they come home because they're about to see their families," said Jaeggi.

"Or the guys who encounter people on the way home and get to show off their hunting skills...none of these things affected the oxytocin change.

The magnitude of the increase didn't differ about these social variables."

Another exciting correlation, Trumble noted, is that the average Tsimane hunt lasts eight and a half hours, roughly equivalent to a workday here.

Though the sample size is "not huge," he and Jaeggi noted, the study "definitely adds to the current literature in which the interplay between testosterone and oxytocin is often overlooked."

More than anything else, the sample size is a function of the cost of the lab assays needed to measure the oxytocin.

"One of our plans is to develop our assay to make it less expensive so we can analyze much larger samples," Jaeggi said.

The Studies Will Continue

Jaeggi and Trumble are careful to point out that an inherent problem in their research has to do with the fact that oxytocin has two distinct release systems: one in the brain and one in the rest of the body.

Therefore, their measure of oxytocin circulating in the blood may not correspond to levels in the brain.

"Some of the social effects of oxytocin might be happening in the brain, and we aren't necessarily capturing that with the saliva sample," Jaeggi explained.

"Of course in this kind of study, all we can do is measure peripheral oxytocin. Measuring oxytocin in the brain would be highly invasive."

According to Trumble, oxytocin studies in the U.S. often make use of nasal sprays to administer the hormone.

"There's a set of tissues right where arteries meet the brain called the blood-brain barrier. Any molecule above a certain size can't pass through it," he explained.

"But there's a weakness in the blood-brain barrier in the nasal canal and allows some transfer to occur. So many experimental studies of oxytocin don't measure oxytocin levels at all, but instead, administer oxytocin and examine before-and-after changes in behavior."

The researchers added, however, that one significant variable adds validity to their work: their ability to study the endogenous levels that are changing naturally rather than from experimental administration.

"With the nasal spray, people are getting colossal concentrations of oxytocin; it can increase their circulating levels to over 100 times the normal physiological levels," Jaeggi said.

"And if there's a change in behavior, it's not the body itself that's producing the changes."

Just as significant, Jaeggi and Trumble noted, is their focus on the interaction of the two hormones.

"Most researchers tend to look at oxytocin or testosterone one at a time," Trumble said.

"But the endocrine system is complex and interconnected, so understanding how changes in testosterone impacts oxytocin and vice-versa is vital."

As running laboratory analysis such as those in this study become more affordable and also become more prevalent in the scientific literature, researchers will be closer to unlocking some of the secrets of the brain and human behavior in ways not previously possible, particularly with the current model of studying one hormone at a time.

"One of the keys to the future of really understanding human behavior is going to be looking at a whole host of hormones together, all at the same time," Trumble said, "and starting to understand those complicated interactions.

Absence, it seems, really does make the heart grow fonder.

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