Hormone study (oxytocin) finds monkeys in long term relationship look strangely human

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tamarinsMonkeys in enduring relationships show a surprising correspondence in their levels of oxytocin, a key behavioral hormone,
according to research published online June 28 in the journal Hormones and Behavior.

While measuring oxytocin in the urine of 14 pairs of cotton-top tamarins,Charles Snowdon, a University of Wisconsin-Madison professor of psychology, observed a wide range of hormone levels.

But he also saw a striking correspondence among the couples: When one mate had a high level of oxytocin, so did the other, and vice versa. Furthermore, partners with a high level of oxytocin performed correspondingly more cuddling, grooming and sex, while those with low levels of oxytocin spent less time on these relationship-building activities.

The hormone oxytocin was originally studied for its role during childbirth, when it helps cement the mother-child emotional attachment. More recently, it has been linked to many other attachments. "Only in the past 20 years have we started to think more broadly about oxytocin's social function in forming and maintaining long-term relationships," says Snowdon.

In monogamous mammal species, he says, "We see that oxytocin in parts of the brain in females leads to pair-bonding." An oxytocin nasal spray makes people more willing to trust strangers.

Oxytocin rises after orgasm, massage and petting. "All this together suggests that oxytocin would play some role in creating strong pair bonds in these cotton-top tamarins, who are socially monogamous," says Snowdon, "and that the amount of cuddling, grooming, stroking and sex might be related directly to the oxytocin level."

In the new study, Snowdon, Toni Ziegler, a scientist at the Wisconsin National Primate Research Center, and their collaborators measured urine samples for oxytocin and recorded behavioral activity three times a week for three weeks, and then noticed the surprising correspondence between both members of the pairs.

Predictably, the study showed that high oxytocin among females was associated with more cuddling and stroking, and that among males, the major element was the amount of sex.

Snowdon may have been the first to respond "Isn't that familiar!" to this part of the results: It doesn't take a high-tech lab to notice that women and men have different emotional and physical needs, and the monkeys seem to echo this need.

But he noticed something else: The high-oxytocin monkeys seem to know how to soothe their partners. In previous studies, after monkey pairs were mildly disturbed either by removing one animal for a half hour or by introducing the scent of another female, both partners increased cuddling and sex as though to mend the relationship.

tamarin monkeysIn the current study, the partners seem to know what the other partner needed. "Males in a high-oxytocin relationship were more likely to initiate cuddling, and females were more likely to initiate sex," Snowdon says. "These males were initiating the behavior that the female needed for high oxytocin, and the females with high oxytocin were initiating the behavior that male partner needed for high oxytocin."

Snowdon says this "monkey version of 'kiss and make up' suggests that sex and affiliative behavior may play an important role in maintaining a relationship."

Stroking, sex and cuddling are critical parts of what it means to be a cotton-top tamarin, and to be human, Snowdon says. "Here we have a nonhuman primate model that has to solve the same problems that we do: to stay together and maintain a monogamous relationship, to rear children, and oxytocin may be a mechanism they use to maintain the relationship.

Therapeutically, I'd suggest this would have relevance to human couples."

July 12, 2010
by David Tenenbaum

Original article

Karezza combines both sex and cuddling (the two behaviors observed here) very effectively. It would be nice to know how often tamarin-monkey sex results in orgasm. Some primates only ejaculate in about half of encounters.


a problem of effect magnitude?

Similar research (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2034242/) in rats has been included in at least one science article (http://www.reuniting.info/science/oxytocin_health_bonding), so the post-orgasmic oxytocin elevation has support from at least two species and is probably widespread. But is it not the case that the conclusions Snowdon draws from his primate work contradict our basic operating assumption, namely that orgasm does not promote bonding?

One quote from this summary is most perplexing, particularly because the monkeys in this study were only socially monogamous, which is ostensibly not the goal of the type of human monogamy that was mentioned later in the article:

Predictably, the study showed that high oxytocin among females was associated with more cuddling and stroking, and that among males, the major element was the amount of sex. ...and... These males were initiating the behavior that the female needed for high oxytocin, and the females with high oxytocin were initiating the behavior that male partner needed for high oxytocin.

Oxytocin released during non-orgasmic bonding behaviors is likely to strengthen the pair bond, but what about the oxytocin released after orgasm? Is there some competition occurring between neurochemical pathways? Both oxytocin and dopamine surge during/directly after orgasm, so is it the case that the satiety and ultimately the dissatisfaction induced by the dopamine spike and crash is more consequential than the oxytocin elevation? Is it possible that the study somehow confounded the effects of non-sexual bonding behaviors and sex?

Without a concurrent study of dopamine, and in the absence of novel partners (apparently the monkeys were not given the opportunity to actually copulate with the females whose scent was introduced as a 'mild disturbance'), this study seems to fail to address the dopamine-based mechanism for dissatisfaction and novelty-seeking. From a single-datum (i.e. personal) perspective, ++oxytocin post-orgasm does not contribute to harmony in my relationship, and this appears to be the experience of many others. I am skeptical about the 'therapeutic relevance' of this particular oxytocin study because it fails to account for dopaminergic effects. In short, if orgasm-induced oxytocin boosters really contributed to pair bonding, then episodes of high-frequency sex should improve a relationship, but the reality is precisely in opposition.

Perhaps I am failing to understand a key point; if so, I would be grateful if someone could point out my mistake.

How long does Oxytocin last?

It would seem to me that the release of Oxytocin probably drops off rather dramatically after orgasm, particularly as the Coolidge effect kicks in. I found that engaging in additional bonding behaviors after an orgasm really helped counter the Coolidge effect. By keeping the oxytocin pumping, it seemed to help lessen the post orgasmic drop off, but it was still noticeable, nonetheless.

Unfortunately, I have no scientific information to back this half-baked theory. I wonder if there has been any studies on how long oxytocin lasts in the blood stream once it is introduced. The effects of dopamine seem to last quite awhile, a lot longer than I ever realized. However, the effects of oxytocin seem much shorter lived. That's why I need to go home and get a hug from my honey. I need my daily fix! Smile

The oxytocin

drops off within half an hour in men and women. But I'll ask Gary to to respond to this because he had questions about the research, too. Still it was fun to see someone talking about the power of bonding behaviors...even if they aren't yet looking at the effects of the longer orgasm cycle.

As Gary once said, "If orgasm bonded couples, every john would be in love with his hooker." So clearly there's more to the picture. Also remember that not all primates orgasm during every sexual encounter. They use sex without orgasm as a bonding behavior, too. Something this scientist probably hasn't given a lot of thought to. Wink

Got a nice note back from the researcher

It looks like we share several common interests. I was fascinated by why our monkeys have sex so often and throughout their ovulatory cycles even though we have found that males and females can detect when ovulation occurs. We started noticing that with minor perturbations in relationships- adding the smell of a novel female, even short 30 min separations led to increased affiliative and sexual behavior so the likely link to oxytocin soon became obvious.

What i think is interesting that a monogamous monkey with no cultural norms about what "should" be the appropriate behavior shows close similarities to what you have been writing about for human couples suggesting that these may be universally important in maintaining monogamous relationships.

If anyone is interested in the full study, PM me. Otherwise we may post more about it when we've had a chance to digest it.

And a bit of our further exchange

I wrote:

I have a peculiar question, which I couldn't figure out from your PDF because I wasn't sure what a "successful mount" means (actual copulation, or both copulation and ejaculation). So here's the question: Do you know roughly how often tamarin males ejaculate when they mount? (I assume no equivalent information about females is available.) I was curious to see that for macaque's it's about half the time, and that bonobos also frequently engage in sexual behavior without ejaculation (or obvious female climax).

Could it be that the act of copulation is the key to bonding for male primates, and that this is true irrespective of climax? And that some primates are best served (in maintaining social ties) by using copulation frequently, and ejaculation less frequently?

From his reply:

Because these monkeys are rather small - little more than a pound - and we housed them in large cages, it was very difficult to tell whether complete copulations with ejaculations occurred. I'm almost positive they did not occur on every mount, but I can't make even an educated guess on what the proportion might be since tamarins don't show anything like an orgasmic response. So 'successful' simply means the female did not turn the male away (which they may often do).

Although there is some research in humans showing that oxytocin rises at orgasm, I agree with you that the physical contact of making love (without necessarily resulting in orgasm) would be important and that orgasm is simply a nice and fun add-on when it happens.

What the monkeys do is mount at least once a day in our observations, and in the early stages of relationship formation, they may be mounting several times an hour.

I suspect that the more frequent rates of touching and sex we engage in during courtship (compared with being old married couples) may also be part of a learning mechanism-- I associate the sight, smell, voice of my partner with the physical and hormonal sensations, and then in the future her voice, her picture or her smell can help substitute for the tactile feelings, and let me maintain the relationship with less physicality (though physical contact will still be important to sustain and maybe more importantly to repair our relationship).

Here are some excerpts from the full study

*sigh* It's so easy for this type of research to fuel the current myth that "sex is good for you and good for your relationship" MUST ACTUALLY MEAN "orgasm is what is good for you" (and even, in the case of males, that a partner is optional).

And yet, from a karezza perspective, it seems evident that what this study really shows is that comforting touch that includes some sexual arousal, keeps both mates contented and bonded. Also note that when sexual activity was pulled out of the stats, the pairs still showed high oxytocin correlation. Demonstrating the power of bonding behaviors, independent of sex. (Mind you...I like sex! Just saying... Wink )

Notice that mere erections seemed to be as effective (at producing oxytocin) as copulations in the case of male oxytocin levels. (And remember that the researcher said he doubts all copulations involve ejaculation.) And yet, the summaries of the research just say "sexual activity," which a mainstream reader would probably equate with "orgasm." Or at least which a mainstream reader would think meant, "Oh...I can pick any old sexual activity, so I'll take sexual activity with orgasm thank you very much!" Yet, for all we know, too much orgasmic sex would make tamarins cranky too. Wink

Also notice that when the researchers took out the sexual behaviors (from the stats), the non-sexual bonding behaviors alone showed the same correlation. (Not that I don't like sex, mind you. Just saying...)

It was touching that each gender seemed to know which behaviors would repair the relationship best. To mend fences, the females solicited sexual activity, and the males snuggled up.

Here are some of the excerpts I found interesting:

We classified behavior into two broad
categories, mutual behaviors that involved both members of the pair
(and were thus scored for the pair rather than the individual, except
grooming, see below), and individual behaviors. Mutual affiliative
behaviors were huddling (animals in body contact with tails curled,
duration and frequency recorded), proximity (within a tamarin arm's
reach, duration recorded) and grooming (identity of groomer, duration,
and frequency of bouts recorded). Mutual sexual behaviors included
solicitations by both sexes and all mounts by males whether successful
or not. Individual behaviors included female solicitations (vertical
stretch directed toward mate with body rubbing on substrate),
erections (by males), headshaking and tongue flicking, investigation
(sniffing or licking of genitals of mate), initiation of proximity,
grooming by one individual, female scent marks, male investigation
of scent marks (within 5 s of female marking).

...Pair oxytocin levels correlated significantly with
affiliative behavior (RS = 0.783, n = 14, P b 0.01; Fig. 3). When sexual
behavior was removed as a variable using only the rank order based
on huddling and grooming frequency and duration the correlation
with pair oxytocin rank was still highly significant (RS = 0.72, n = 14,
P b 0.02). ...

In contrast to previous research on rodents (polygynous rats
and monogamous prairie voles) where sexually naïve females had
increased levels of oxytocin compared to sexually naïve males
(Kramer et al., 2004) we found no sex differences in oxytocin levels
[in tamarins, who share parenting duties].

... However, our data suggest
that oxytocin levels are stimulated by different behavioral variables for each sex.

An unexpected result was the 10-fold variation in oxytocin levels
across individuals. [However, variations in a vasopressin gene have been found in male voles and male humans. Vasopressin is a cousin to oxytocin, and can induce protectiveness toward a mate.]

We also found corresponding variation
in measures of affiliative behavior across pairs. Our results suggest
that variation in affiliative and sexual behavior may have a significant
effect on hormones or vice versa. This variation in hormones and
behavior within species has clear implications for understanding
human behavioral variation in affiliation and pair bonding.

We also found a significant correlation between oxytocin levels in
both males and females within tamarin pairs that suggests that
complementary behavioral interactions may be responsible for the
shared oxytocin levels. Some studies have shown that sexual activities
as well as gentle stroking and touching can elicit increased oxytocin
levels in humans (Uvnäs-Moberg, 1998; Krüger et al., 2003; Light
et al., 2005). Our multiple regression analyses identified two pair
behavioral components (sexual behavior and frequency of affiliative
contact) that explained 60% of the variance in the mean oxytocin
levels within pairs. In addition three individual behaviors, male sex,
male initiation of huddling and female solicitation, explained nearly
83% of the variance in pair oxytocin levels.

... Our results suggest that
chronic levels of oxytocin may be maintained through high levels of
affiliative and sexual behavior.

...Regression analyses showed that variation in oxytocin levels was best
explained by different variables in each sex. For males, frequency of
pair sexual behavior explained 45% of the variance and male erections
explained 43% of the variance. For females the best model excluded
sexual behavior but showed that 40% of the variance in female
oxytocin could be explained by the frequency and duration of contact
behavior and grooming. These results based on pair behaviors suggest
males and females have complementary behavioral strategies with
female oxytocin levels being influenced by amount of proximity and
contact they receive whereas male levels are affected by amount of
sexual activity. It is interesting that analyses of individual behaviors
suggest that mates may be responsive to each other's needs. Male
initiation of huddles with females and female solicitation of sex were
both important variables in explaining variation in both pair and
female oxytocin levels. A good relationship between pair-mates may
be one where each sex can respond to the behavioral needs of its mate.

... Pairbonds can also be formed without extensive sexual behavior. In tamarins
sexual behavior may be important in pair formation as we have
observed high rates of sexual behavior in newly formed pairs (Savage
et al., 1988). However, tamarins also engage in high rates of
nonconceptive sex not only over the female ovarian cycle but during
pregnancy as well. We have reported (Snowdon and Ziegler, 2007)
that rates of nonconceptive sex and female solicitation increase after
minor threats to the relationship (brief separations, and olfactory
stimuli from novel reproductive females) suggesting that nonconcep-
tive sex may be important in restoring or maintaining a relationship.

...We suggest that the amount and quality of close contact
and nonconceptive sex may also play an important role in predicting
the quality and duration of human heterosexual relationships. The
demonstration that both sexes of tamarins have equal levels of
oxytocin within a pair, but that these levels are influenced by different
behaviors for each sex and that each sex engages in behavior that
complements the needs of the mate suggest ways in which human
relationships might be improved.

Again, bonobos and macaque monkeys often engage in sexual activity without climax, so it seems like some primates really understand the karezza principle, even if few humans do. Wink

those monkeys

I just have to say that those monkeys are so cute.
AND... that I love all these studies done on the relationship between oxytocin and bonding between partners.


they're adorable.

The research is exciting, because it's so consistent with what we've been learning about bonding behaviors.