Monday, January 19, 2009

Oestradiol makes women hot and hard to keep

ResearchBlogging.orgThe estrogen hormone oestradiol is associated with just about every aspect of female beauty. As well as serving as a growth hormone for female reproductive organs, it's associated with having a symmetrical face, large breasts and a low waist-to-hip ratio. Now, the hormone is credited with one more association: it makes women serial monogamists.

Marilyn Monroe

Her relationships explained
by her body cheimstry?

For those who may not have heard of this term, let me explain. A serial monogamist is a person who has sequential relationships, and who tends not to spend much time alone in between partners. While they make what seems to be a lasting commitment to each person, they tend to be superficial, get bored of their significant others easily, and find a new one every so often.

Well, new research has linked oetradiol levels to this kind of relationship behavior.

University of Texas researchers polled women about their personal and sexual behaviors and compared their responses to their saliva oestradiol levels. They also took pictures of the women for an independent analysis of beauty. They found that while the high-oestradiol women were more attractive than their counterparts (by the women's self opinion and independent judges), they also had significantly lower levels of satisfaction with and commitment to their parters and a greater likelihood of infidelity.

Specifically, the women were more likely to have serious affairs, but not more likely to have brief sexual encounters. So they weren't simply more sexually active - they were picky, too. They preferred long-term commitments but were less satisfied by them. So women with high oestradiol levels are classic serial monogomists. This is strong evidence that physiological mechanisms may be a much larger part of mating behaviors and strategies than previously assumed.

This means that your role models may have less to do with how you act in relationships than you might think, at least if you're a woman. But there's one more thing that makes this study very interesting. A synthetic form of oestradiol, called ethinylestradiol, is a major component of hormonal contraceptives, which many women who aren't married but are in relationships take so they can have all the fun of condom-free sex without the risk of getting pregnant. Now, if women are taking this hormone every day, how much is it affecting their behavior? Are the ingested levels enough to make a difference? Are birth control pills changing modern women's mating strategies? Or, more bluntly, is your girlfriend's birth control making her more likely to cheat on you?

Just some food for thought...

Kristina M. Durante, Norman P. Li (2009). Oestradiol level and opportunistic mating in women Biology Letters, -1 (-1), -1--1 DOI: 10.1098/rsbl.2008.0709


Anonymous said...

Well this explains some things. And if the contrary is true...perhaps being thicker-waisted leads to a longer lasting happier married life?

Bjørn Østman said...

Fascinating. The level of pleiotropy is astounding.

One must be careful with the causal relationships, though. What causes what, here? Are we certain that Oestradiol actual is the causal factor in making women serial monogamists?

It's not that I don't believe it. In fact, I am of the tentative conviction that much of our behavior is (partially) determined by factors we don't control, while the reasons we normally give for our behavior are secondary justifications.

And speaking of... You aren't out to justify this immoral behavior by explaining it, are you now, Christie? There are people out there who might confuse the two. LOL!1!

Christie Lynn said...

Yes, I agree that there must be care in saying correlation is causation... but at least this one is funny.

and LOL... now now, who says that it's immoral to upgrade every once in a while? ;)

Bjørn Østman said...

Upgrading your man is sort of discrimination, ain't it?

John said...

Christie -

Great post. I think this explains about half the women I have dated. And you are quite the writer.

I looked all over your website to find an email address for you...with no luck.

Anyway, I was trying to get a hold of you to see if you were interested in writing for my website - nutritionwonderland.com.

Its a new project and Im lining up amateur scientific-type writers. You totally fit the bill. If you have any interest, surf your way over there and click the 'suggest a story' link to email me.

It would be great to hear from you,

Margaret said...

It is fascinating stuff. I just wanted to pick up on one point you raised:

"Are birth control pills changing modern women's mating strategies?"

Research into the Major Histocompatibility Complex has demonstrated that women tend to be attracted to men with substantially different genes in that region. This helps insure that offspring have a more efficient immune system. During pregnancy, the attraction is reversed. Women tend to prefer intimacy with people with like MHC, probably because their families will be supportive and protective of them during pregnancy and it is preparation for bonding with the offspring.

But when women are on the contraceptive pill, the hormonal effects mimic pregnancy. Thus, when on the pill, you're more likely to be attracted to men with a similar MHC. So if you meet your partner while you're on the pill, then go off the pill when you've decided you want a family, serious trouble can brew. Indeed, there is research supporting the notion that it is at exactly this point that a substantial number of marriages fall apart.

It also raises the issue of those offspring in relationships which started when the woman was on the pill. Is a substantial proportion of the subsequent generation going to have less effective immune systems?

I know one thing. When my daughter gets to the "falling in love" age and wants to use contraception, she won't be using the pill!

Interrobang said...

I have large breasts, no waist indention to speak of (that's something that happens when your ribs sit on your hips; someone forgot to run that part of the build when I was in utero, I guess), and I'm a serial polyamorist. I'd happily settle down with the shifting set of four or five people who were right for me at any given time, but this monogamy thing stinks on ice. I love my boyfriend and I'm not into superficial relationships, but I honestly don't understand how it's possible for one person to meet all of another person's intimate emotional and physical needs. Or maybe I'm so weird it just takes more than one in my case.

I've also been on the Pill since I was 17. Make of that what you will.

Margaret said...

If anyone is interested, here is a paper on MHC and the contraceptive pill: http://journals.royalsociety.org/content/f542428772r96x64/fulltext.pdf

Chad said...

So, are you seriously making an argument that the complex decision-making process of mate selection in women is governed by hormones? Reading the abstract of the paper, I do not think that is what the authors intended. It is also not supported by the wide variability in what is considered attractive across the spectrum of human cultures and time periods. Such an analysis seems both sexist and euro-centric in nature.

Isn't it just as easy to assume that 'hot' women have a wide variety of mates choices available to them, that they tend to pick mates of high social value (because they can), are more likely to stick to those choices because of their value, but are less satisfied with their choices because society tells them that they are 'hot' enough to do better? The same thing happens when you buy a new car... no matter how happy you are with it, the next year's model always looks better. This seems like a much simpler explanation.

Chad said...

And to add a comment about being on the pill... if you are a woman on the pill and have no children, married or not, you have much more flexibility in your relationship. Break-ups are relatively easy, and divorces are primarily about stuff. Once a couple decides to have children, the relationship stresses can be incredible. It isn't all Ozzie and Harriet out there. Core problems in relationships become magnified as the thought of being permanently tied by a human bond becomes pervasive. So, wouldn't that be a more rational explanation for marriage failure after the pill than a hormonal spike?

Christie Lynn said...

Well... I wouldn't say "governed", per se, just that hormones may have a larger role than we think. And clearly this study was far from conclusive and all-encompassing in its results.

However, it is still interesting that these women had significant differences in attitude and behavior. You could look further into this: do women that we consider 'hot' but are skinny and small breasted (and have lower oestradiol levels) have the same attitudes? If it's just that they're 'hot' enough to always do better, you would expect no difference between the groups. It would be interesting to probe into variation within attractive women and see if their oestradiol levels still correlate with their satisfaction and likelihood of cheating. Again, this study is hardly comprehensive, and can't answer that kind of question. And as far as marriage failure after the pill, what you propose is definitely possible, but again, I would be interested in seeing the data. Are high-oestradiol women who have kids still more likely to leave? It's possible - and the study (and what we know of celebrity marriages) would suggest that they are. So again, I'd like to see a comparison of women that are attractive and have differing levels of oestradiol, to see if there's any differences in behavior. I think that would be the real 'tell' of whether this hormone can alter behavior.

To suggest that hormones have nothing to do with mating strategies, I think, is silly (not that you are saying that). Of course they do. The question is really to what extent. And of course, this brings in hormonal treatments like birth control. Isn't it at least possible that the hormonal birth controls have an effect on a woman's behavior? I would also like to see someone look into these kind of attitudes and behaviors before and after women go on the pill, for example. There's a lot more to look into, but I think the study itself is still very interesting and raises a lot of questions.

Margaret said...

Chad: "So, wouldn't that be a more rational explanation for marriage failure after the pill than a hormonal spike?"

The effect is found not only when children are produced, but when the woman simply changes her form of contraception, so no, that wouldn't be a more rational explanation.

No one is suggesting that MHC is the only influence on mate choice. Obviously, there is a vast range of other factors. And if you read the paper I posted, it's not talking about a "hormonal spike", but the effect of pheromones that are governed by the genetic makeup of an individuals MHC. The evolutionary pressure leading to the development of such sexual strategies should be obvious.

If you did a little more reading in the field of the biology of human sexuality, you'd find that across cultures, there is in fact an extraordinary similarity in what people find attractive, that exists in addition to regional and cultural factors. Clear skin, for example, which indicates a low parasitic load (and thus cam reflects a greater genetic ability to withstand parasitism). Facial symmetry, which shows an in-utero ability to compensate for various uterine pressures. These correlate with genetic fitness, and the genetic fitness of a mate is paramount in evolutionary terms.

Female facial symmetry even increases during ovulation (caused by the swelling of fleshy regions of the ears, nose and cheeks), a form of dishonest sexual cue. Female behaviour changes dramatically during ovulation, with women tending to wear closer fitting clothes, preferring the company of multiple men, and being more attracted to "masculine" men. When a man's sexual partner is ovulating, he is more likely to "mate guard", even if he is completely unaware she's ovulating. If he returns after an absence during which she might have had extra-pair copulation, he produces more sperm to overwhelm any other sperm present in her genital tract. These are unconscious responses to social circumstances and hormonal and pheromonal signals.

While I give due recognition to social and cultural variation within our species, the fact remains that we are animals that have evolved our sexuality over millions of years, and as such, profoundly influenced by our biology and what is ultimately the role of any living creature: to replicate its DNA.

(If you are interested, I can post a reference list of peer-reviewed papers supporting my assertions.)

Anonymous said...

Hi everyone, having had ever so often to contemplate my normality, maturity and capacity for emotional deepness and having hurt quite my share of ex-boyfriends deeply in the past, I can only say to everyone in here that it is NOT funny AT ALL over time!!!
But a relief to finally find some sort of explanation, especially since the "psychological" profile is me in a nutshell, relationshipwise..

Anonymous said...

Hi, just wondering, I was put on the pill at 11 ys, and only stopped about 3 years ago, after 18 years with pills. After wich I hooked up with a man I knew when I was on the pill, whom I find exactly as attractive now as before..
Plus, what explains the cheating men..?
Plus, maybe the oestradiol-production of "hotter" women is triggered by the extra attention they get from the men around them - it could easily be a two-way mechanism. I mean, there might be other women on this forum who has experienced what flirting with a guy who feels "right" does to you - must be hormones brewing??

Christie Lynn said...

Anonymous on Jan 23rd:
The effects of birth control pills on this sort of thing are complex, and certainly not covered in this particular study. I was just pointing out that we pump our bodies full of hormone mimics without understanding the effects of the hormones in the first place - which is dangerous territory.

As for men, that's a whole other problem - spreading their seed and all. There's some good books that go in depth about the male drive to cheat... but safe to say it's them and their damned billions of sperm that make them prone to it.

As for oestradiol release socially, that's entirely possible - as far as I know no one has looked at that closely. Sounds like an interesting project/paper :)

Anonymous said...

Oestradiol is related to teh fertility cycle