Rationally Speaking is a blog maintained by Prof. Massimo Pigliucci, a philosopher at the City University of New York. The blog reflects the Enlightenment figure Marquis de Condorcet's idea of what a public intellectual (yes, we know, that's such a bad word) ought to be: someone who devotes himself to "the tracking down of prejudices in the hiding places where priests, the schools, the government, and all long-established institutions had gathered and protected them." You're welcome. Please notice that the contents of this blog can be reprinted under the standard Creative Commons license.

## Thursday, August 16, 2007

### Promiscuity 101

A recent article in the New York Times has brought to the fore a question I'm sure has been bugging many readers of this blog: if men are supposed to be promiscuous and women are supposed to be shy, who, exactly, are the men being promiscuous with?

First, the facts, such as they appear to be: the results of survey after survey are remarkably consistent in indicating that men have more sexual partners, on average, than women. According to a recent study conducted in Britain, the figures for the median are 12.7 and 6.5 respectively (interestingly, the corresponding numbers in the United States are 7 and 4, what's up with that?).

But, argues math professor at the University of California at Berkeley David Gale, this cannot logically be. He even provided the Times with a mathematical proof that should settle the matter definitively :

“By way of dramatization, we change the context slightly and will prove what will be called the High School Prom Theorem. We suppose that on the day after the prom, each girl is asked to give the number of boys she danced with. These numbers are then added up giving a number G. The same information is then obtained from the boys, giving a number B.

Theorem: G=B

Proof: Both G and B are equal to C, the number of couples who danced together at the prom. Q.E.D.”

Well, not so fast. As a smart (female) friend of mine quickly pointed out, there is a huge hole in this proof: it assumes that people “dance” only with one person at a time, and that dancing is balanced throughout the evening, so that if a girl doesn't dance there will be a corresponding boy who doesn't either.

But one wonders in what kind of world professor Gale lives. Biologists have produced plenty of evidence that many animal species, including mammals and particularly primates, easily violate both assumptions. I remember an old Italian joke appropriate to the situation in question: “Every man has, on average, seven women in his life. If I catch that son of a bitch who's got fourteen...”

Of course, Gale has a legitimate point when he cautions social scientists against accepting self-reported figures at face value: critics of self-report surveys point out that the surveys themselves may reinforce the stereotype of promiscuous men and chaste women, which then influences the way respondents answer the question, which reinforces the stereotype, and so on in an increasingly vicious circle. Although difficult, however, it is possible to come up with independent means of checking the reliability of self-reports. One would have to conduct DNA tests in random samples of the population using hospital birth records, comparing genomic markers of newborns with those of the (alleged) fathers. The relatively hard science of molecular biology could then come to the aid of the relatively soft one of sociology. We might finally be able to see whether Woody Allen was right when he said “Sex without love is a meaningless experience, but as far as meaningless experiences go its pretty damn good.”

1. I recall a report of an unpublished study that showed, just on A-B-O blood types, that a startlingly high percentage of children could not have been the offspring of the reported father.

To put a rather cynical viewpoint on it, women could (and sometimes do) marry for resources, and mate for good genes.

2. "One would have to conduct DNA tests in random samples of the population using hospital birth records, comparing genomic markers of newborns with those of the (alleged) fathers."

In line with John's comment, the unspoken premise of the above extract is that all promiscuity results in live births, which is obviously not the case.

3. T "In line with John's comment, the unspoken premise of the above extract is that all promiscuity results in live births, which is obviously not the case."

But what does science actually say? I think some men claim to care what science says, but they don't really care at all.

More and more we are going to realize that the "real world" is not so much what happens between people. The real world(in terms of our continued existence) is what happens between viruses and or bacteria. When people choose to be promiscuous, live births could be the very least of the worries, all the while it is viruses that are exchanging the truly critical(to the rest of your life kinda) information.

A friend of mine worked as a supervisor in the dept at UNM where the vaccine for the HPV (and HIV) was developed. But according to my obgyn that particular vaccine for HPV is not to be thought of as a "cure" as it is being purported to be. It actually only addresses about four strains of HPV, and there are a lot more "out there" than four. As a matter of fact, he also said that over 60% of men and women are already carrying some form of HPV. I think that medical science is really beginning to understand that it is this type of virus which often leaves the door wide open for cancers in the reproductive organs.

Is that what we all wanted and asked for?

Well, yeah, sort of.

Prophylactic and birth control promotions are at least partially to blame for the rise in these types of deadly diseases in women, and even to a certain extent in men. Women should NOT be at all fooled by the propaganda on this vaccine. Babies most definitely are not the only price that women will pay when not opting to protect themselves.

ever the realist..

cal

4. T "In line with John's comment, the unspoken premise of the above extract is that all promiscuity results in live births, which is obviously not the case."

But what does science actually say? I think some men claim to care what science says, but they don't really care at all.

More and more we are going to realize that the "real world" is not so much what happens between people. The real world(in terms of our continued existence) is what happens between viruses and or bacteria. When people choose to be promiscuous, live births could be the very least of the worries, all the while it is viruses that are exchanging the truly critical(to the rest of your life kinda) information.

A friend of mine worked as a supervisor in the dept at UNM where the vaccine for the HPV (and HIV) was developed. But according to my obgyn that particular vaccine for HPV is not to be thought of as a "cure" as it is being purported to be. It actually only addresses about four strains of HPV, and there are a lot more "out there" than four. As a matter of fact, he also said that over 60% of men and women are already carrying some form of HPV. I think that medical science is really beginning to understand that it is this type of virus which often leaves the door wide open for cancers in the reproductive organs.

Is that what we all wanted and asked for?

Well, yeah, sort of.

Prophylactic and birth control promotions are at least partially to blame for the rise in these types of deadly diseases in women, and even to a certain extent in men. Women should NOT be at all fooled by the propaganda on this vaccine. Babies most definitely are not the only price that women will pay when not opting to protect themselves.

ever the realist..

cal

5. Hmmm... I don't think I get the "impossibility" in those numbers at all, so either I'm drooling here (likely) or Dr. Gale is kinda crazy. Well, given he's professor emeritus of math and I am a biologist who can barely count...

But here goes my "reasoning" anyway for you guys to criticize -- maybe it's the same thing Massimo's friend said, just in my verborrhagic style. What is the median? It is the value which is exactly in the middle of all other, i.e. 50% of women have 4 or fewer partners and 50% of women have 4 or more. The median is calculated putting all the number in order and then picking the one in the middle. So, consider the sequence:

1 3 4 5 7 23 98

The median here is 5, because that's the value in the middle (the mean, or average, would be the sum of all those, divided by seven, a.k.a. 20.14)

Where am I going with all this is: the median is as informative as the distribution is relatively uniform, without crazy outliers. So let's (hypothetically) say that 30% of women have 30 partners over their lifetime, while the remaining 70% have the proverbial 4. The median will still be 4, of course. Even if nobody is "dancing" with more than one person at a time. :-)

Where did I go wrong? Did I?

I'd rather be improving my statistics for when those damn survey people show up, actually... :O)

6. Second post (and not a repeat!): the infidelity data John and Thumpalumpacus hinted at. Yes, that sure would be a minimal estimate (given the obvious fact that not all infidelity results in a pregnancy).

An article discussing why women cheat, but the following passage is of special interest:
The first reliable estimate concerning infidelity was made in 1953 by renowned sex researcher Alfred Kinsey, who in his landmark study found that 50 percent of husbands and 26 percent of wives surveyed had cheated by age 40. However, in recent years, women have been catching up to men. A 1997 Ball State University study suggests that young women, those under age 40, are just as likely to commit adultery as men their age. Among older couples, the stereotype of men being more likely to stray holds true.

So, either times'a'changing or women are speaking more the truth or, probably, both.

Another interesting read is this first chapter of a book called "Female Infidelity and Paternal Uncertainty", subtitled "Evolutionary Perspectives on Male Anti-Cuckoldry Tactics"

This is a more standard scholarly thing, with references and all that. They cite the American Association of Blood Banks data that analyzed 280,000 paternity tests (in 1999) and came up with 30% of children fathered by what they call "extra-pair copulations". Gotta love that technical jargon. A poor chap in Texas for example went from having 4 kids to having just one, in the drop of a hat. I mean, test tube.

In spite of this big, impressive 30% number (which could be an underestimate, if you consider also that there are cases where the blood group of the cheated "father" and the biological one will be the same, or not mutually exclusive), they point out that there are estimates of female infidelity ranging from 1% to 30%, with the best estimate at 10%.

Have fun with those texts and numbers, y'all. Just don't get too paranoid, OK? :-)

7. Median is not Mean.

8. "critics of self-report surveys point out that the surveys themselves may reinforce the stereotype of promiscuous men and chaste women, which then influences the way respondents answer the question, which reinforces the stereotype,.."

This I think is an important point. There are cultural pressures for men to exagerate the number of their partners, and for women to minimize the number. And even if the respondent knows that the survey is confidential or anonymous, these cultural pressures may end up influencing what the respondents actually believe about themselves.

Speaking of which. What was the name of that pro basketball player who claimed that he had relations with some ridiculous number of women? Doing the math it worked out to him having to have sex with 3-4 different women per day for 30 years or something like that.

So I rest my case! Men with just a fraction of the bravado and imagination of that basketball player would consistently skew the mean!

And Cal, how exactly is your comment really related to what we are discussing here? Only tangentially is it relevant. As usual you attempt to derail the discussion.

9. Simple explanation: men exaggerate, women understate.

10. @The Ridger, fdc:
Yeah, she is. She won't share.
---
Cal, you can feel guilty about recreational sex if you like, but leave the rest of us alone.

11. Following up with my last comment.
It was Wilt Chamberlain who claimed to have had 20,000 different sex partners throughout his life. (now thats a sports stat!).
http://en.wikipedia.org/wiki/Wilt_Chamberlain

He lived to the age of 63. Assuming that he began his sexual adventures at the age of 15, and continued until he neared death, he had 48 years of sexual activity, requiring him to have relations with 416 women per year, or on average 1.18 women per day. Busy man!

http://espn.go.com/nba/news/1999/1012/110836.html

Apparently Wilt had actually done the math and wrote about it in his auto-biography! And it would seem he actually believed it to be true as suggested by the espn article!

12. Oops correction. Wilt Chamberlain made the claim in 1991, which would give him 40 years of sexual activity, 500 women per year, and 1.42 women per day. I am sure you all are as facinated about this as I am! LOL

13. I think that women and men are definitely socialized in different ways. As the only female in a brood of 5 children, I was definitely constrained sexually--not even allowed to date until just before graduating from highschool. My brothers were freer in their social relations.

Standards of socialization for men and woman, however, are changing. In the past, women were socialized to 'act' shy, especially in response to sexual overtures from men. Sexual aggressiveness in females was considered a faux pas, unfeminine, even b--chy. Its all rather medieval, these social contracts and assumptions.

Now, more women project the same aggressiveness that men have laid claim to for years. I don't have any great edicts to levy against promiscuity. Yet, as a result of the tearing down of constraints, the leveling of high standards (sometimes impossible to maintain), consequences will arise--pregnancies, dieseases, single-parent households, and so forth.

This blog gives a biological edge to the topic, but maybe the social construction of modern society is at the crux of the issue. One can analyze the 'promiscuity' issue with respect to social constraints, various prejudices, stereotypes, religion, and more. A promiscuity explosion may be the result of the medieval code of threading one's animal desires through too rigid an iron grid of moral behavior? Sounds like a set up for a severe neurosis; and, possibly, more promiscuous behavior in the future.

14. sheldon, kimpat,

The topic is promiscuity. (& the science of) And just so you know, it always hurts women the most. so if you think it an effort to derail, that is your problem. In essence, you just don't care about what science really says unless it supports your interests

Not particularly respectable in my estimation.

Of course...
It is great to be loved. And it is especially good to be loved unconditionally even if a person makes an occasional errors along the way. BUT IT IS NOT good to be (so-called) loved by a partner who lets one get away with murder. The HIV rate in Africa proves that this is a lesson that certainly can be learned too late. Love should exist for helping people to have long and healthy lives, not sending them to an early grave.

And do i feel guilt about suggesting any of that? NOT ON YOUR LIFE

cal

15. Cal,
The topic may be "promiscuity", but not neccessarily the moral and health consequences of "promiscuity".

The topic is more specifically the alleged discrepancy between men and women's reported number of sex partners over the course of a lifetime.

I don't think anybody here would disagree that there are negative consequences to irresponsible sexual behaviour. But that is not the topic.

Many would however disagree with your idea of what contsitutes irresponsible sexual behaviour. Anything outside of one partner and marriage, I presume?

You want to derail the discussion by interjecting your religious right wing-nut opinions about HPV virus/vaccine, and birth control methods. This is off topic.

"And just so you know, it always hurts women the most. so if you think it an effort to derail, that is your problem. In essence, you just don't care about what science really says unless it supports your interests. Not particularly respectable in my estimation."

What are your talking about? You also seem to want to suggest and portray women as only victims of any sexual encounter outside of one partner and marriage. That is not the case.

Just so you know, since you are implying something, I have no "interests" in the matter. I have had zero promiscuity since meeting my spouse 8 years ago. Before that, I was serially monogamous, with only a few casual encounters in between. None of those women were passive victims of my sexual aggressions, but willing participants and beneficients.

16. Cal, Having read numerous articles about the HPV vaccine, I have not seen one that said it was a "cure", but rather a preventative measure. And isn't efficacy against four strains better than none, especially if the individual is going to be sexually active regardless of the existence of a vaccine or not.

And how can prophalaxis and promotions birth control, be at blame for the spead of disease among women (or men for that matter). Sounds like the Gospel according to George W. Bush. And look where that dogma as gotten us in other areas that he has spewed on about for the past seven years.

17. Oops correction. Wilt Chamberlain made the claim in 1991, which would give him 40 years of sexual activity, 500 women per year, and 1.42 women per day. I am sure you all are as facinated about this as I am! LOL

Did not Brigitte Bardot claim about a partner a day? I find that more fascinating than Wilt the Stilt. Heh heh.

Then there's David Bowie's wife, Angie (of the Rolling Stones song) who more realistically claimed 90-odd lovers.

18. Dennis,
It doesn't matter what you have read. You see, Cal has a friend who worked in a biology lab, so she clearly knows what she is talking about. Besides, if you give those girls that vaccine, then they will figure that with the reduced chances of cervical cancer they can equalize their number of lifetime sex partners to that of men. That would just be awful! You know, women enjoying a varied sex life free from the worries of that cancer! Civilization would collapse!

19. Very interesting post!! Here's something I put together about ten years ago, which seems germane to this topic:

Consider a village of 9 absolutely faithful couples. They've each had exactly 1.0 partners. Now, another couple moves in. He looks like Tom Cruise and seduces the other 9 guys' wives. (hey - it's just a thought experiment!) Now, considering all 10 guys, their total # of partners is 9x1 + 1x10, or 19, for an average of 1.9 partners each. Every woman has now had 2 partners except Mr. Cool's poor wife, who's had only one. This comes out to 9x2 + 1x1, or 19, giving a women's average of 1.9 as well - still the same as the men. Thus it seems that in any CLOSED group, following ANY kind of behavior always gives EXACTLY the same average number of partners for men as for women.

Mathematically, this is because, while the average for, say, men, is defined as the total # of their partners divided by the # of men (M), it is also equal to the # of unique pairings Np (e.g. Bob+Alice) that has ever happened, divided by the # of men. Assuming that a unique pairing involves one man and one woman, this means the "Np" used to calculate the men's average is the SAME "Np" used to calculate the women's average, so if there are the same number of men as women in the group, then their average numbers of partners MUST be identical. (Note that a threesome & up can be treated as two or more serial 'unique pairings', leading to the same result.) Further, if there are, say, more women than men in the group, then the ratio of the two gender averages must be the same as the ratio of the populations. If there are more women, then the men will average more partners, thusly:

Women's average X = Np / W
Men's average Y = Np / M
Ratio of men's average to women's average = Y/X or (Np/M) / (Np/W) or just W/M.
Therefore, surveys indicating that men have nearly twice as many partners as women do are mathematically proven to be impossible in a closed population.

Now of course no sizable real population is sexually closed, so how does this change things? First, realize there is indeed ONE very large closed population, namely planet Earth, and the above equation MUST hold for that. Within that, it can be proven with a little more math that although there can exist a non-closed subgroup where men do indeed have twice as many partners as women, this forces the existence of another non-closed subgroup wherein women have twice as many as men, to keep the global average at W/M as above. (obviously, this reasoning holds only for heterosexual activities)

-KWFco

20. I wonder how many female prostitutes figure in the questionnaires used in these surveys? One such prostitute could equal the lifetime sexual history of several men in a single evening.

21. The inscriptons on the adjacent tombstones of Alaska frontier hero Frank Reese and a lady of the night known only as Annie K.

"FRANK REESE
HE GAVE HIS LIFE FOR THE HONOR OF THIS TOWN.

ANNIE K.
SHE GAVE HER HONOR FOR THE LIFE OF THIS TOWN."

22. "None of those women were passive victims of my sexual aggressions, but willing participants and beneficients. "

Or, in my case, donors.

23. Massimo, you got the Woody Allen quote slightly wrong.

The actual quote is "Sex without love is an empty experience, but as empty experiences go, it's one of the best."

24. Hi Massimo,

Couple of quick notes -- Gale claims that he was / is well aware that medians are not means, but that since the survey data was given with percentages who answered that they had a # of partners within a particular range, you can generate a high and low bound mean from the data -- so "j" is right of course, but there was more data available than just the median. And given those survey results, the mean number of sexual partners had to be different.

Now of course, the proof sucks -- but as "KWFco" notes, it *would* be correct if:
1) it was specified that the total number of boys and the total number of girls at the dance are equal
and
2) B and G are not the total number of dances, but are generated by dividing the total number of dances by the number of boys and girls.

So it doesn't matter whether 1 boy dances with all 6 girls and the other 5 boys just sit there, or vice-versa. In either case, the average (mean) number of dance partners remains the same for both sexes. Nor does it matter if they dance in groups, etc -- again, the average will stay the same.

So for mean number of sexual partners, the same should be true -- as it must be in all organisms with roughly equal sex ratios (in organisms with unequal sex ratios, the average number of sexual partners in the sexes must vary by the skewing of the ratio). It doesn't matter if one bull elephant seal has sex with dozens of females and other males have sex with almost none, whereas the females are all equally choosy and all have sex with the same smallish number of males -- the averages must be the same, if the number of males and females is the same.

Re: the survey data. Gale recognized as well that what the surveys might, in principle, be missing is the rare very promiscuous woman (prostitutes are the usual suspects here, as Suffenus suggests). But Gale suggests that this is unlikely for a number of reasons (mainly that it is hard to get the numbers to work out in a way that makes sense of the survey data).

So the most likely explanation remains that men "round up" and women "round down" in the surveys (possibly not even deliberately), or count differently -- perhaps, pace Clinton, women have a higher standard for what it takes for someone to count as a sexual partner ;)

What other species show is not that the average number of sexual partners can be different for males and females, but rather that you can't move so quickly from the fact of equal average number of partners to views about the *preferred* number of partners. Male elephant seals ;) no doubt prefer to have lots and lots of mates, it's just that most of them are disappointed in that preference. Female elephant seals may prefer rather fewer mates, and manage to work with that preference. The males and females end up with the same *average* number of mates, but do so in different ways and through the expression of very different preferences.

And again, this points out that paternity doesn't matter to this argument, either. It wouldn't matter if one man was the father of every child born in a particular year -- the average of number of matings resulting in a conception would still be the same for both men and women, if the number of men and women were equal!

best,

jk

25. One more note, re: KWFco note re: closed populations. If you *really* want to defend the different numbers, I think you might be able to by appealing to the (in my view pretty sloppy, but whatever) research suggesting that older men have more sex with younger women than older women do with younger men. The basic idea would be that the population isn't closed, as women are removed from the partnering population sooner than are men, and the population size keeps expanding so ever more young women are added continuously. So the idea here would be to imagine that each woman has sex with e.g., people in her own age group at a 1-1 ratio, but with older men at say a 1:2 ratio, because there are so many more young women than old men, because the population is expanding (that is, if say there are 2 young women for every old man, and every old man has sex with one young woman, only 1/2 of the young women will have had sex with an old man, etc.).

This, I think, probably doesn't really account for the survey data, but if you like that kind of thing, could be made to work...

26. Jonathan,

good points, and thanks for the post. However: the mean and the median are the same only if the distribution is normal (well, and for other unlikely distributions, like a symmetrical bimodal). It would be interesting to see whether that is indeed the case.

Also, I wonder if the relevant statistic here isn't the mode (the most frequent value), rather than the simple arithmetic mean (the average) or the median (the middle of the distribution).

As the joke goes, if I got two chicken and you none, on average we both had a chicken each... :)

27. Means and medians, again.

Massimo, you note that the mean and the median are only the same if the distribution is normal, and that it probably isn't for # of sexual partners. That's right, and Gale (claims that he) knows that.

What Gale got from the original survey data were the percentages of respondents claiming to have had a number of partners within a particular range, e.g., % claiming between 0-1 partners, % claiming between 2-4 partners, between 5-8, etc. So if you know that 20% of the male population (say) claims to have between 9-12 partners, you can estimate the range of possible means first by assuming 9, then by assuming 12, and similarly for all the ranges. That is what Gale did. Of course, you don't get *the same* difference between sexes as you do for the median -- rather, you get a *range* of possible differences, and the minimum difference between the means is about 40% (again, according to Gale).

If what you are interested in is, for example, parenthood over human evolution, than the historical modes would be more useful, yes. If what you are interested in are tendencies or preferences, than none of these is particularly useful, and what you need are data on preferences. If you are interested in how reliable survey data is, means would be best here ;)

jk

28. Problem with your Prom analysis. You're assuming the sample size = the population size.

Fact is, there are a few women out there who sleep with a LOT of guys. If these women are missed in the study, it will skew the average of all women's sexual partners down. And honestly, these are not the type of women who participate in those types of studies.

This is why you have differing numbers.

29. No, I don't think it's that simple. The authors of these kinds of surveys are aware of that problem, but it would take an unlikely high number of "outliers" to significantly skew the results.