Not about everything

December 11, 2008

Promiscuity of males and females

Filed under: biology,mystery — takaita @ 20:49
Tags: , , , ,

Sometimes a magazine makes about poll with a question involving the promiscuity of its readers.  Such a poll is of course only meant to write an interesting headline for one of the issues of the magazine. And an interesting headline is of course that there are differences between the promiscuity of the two human sexes.

Differences in promiscuity between males and females are however non-existent, at least when it comes to heterosexual partners. That is because the amount of males and females on this world are about the same. In every heterosexual contact, both a male and a female are involved.  To make the math a bit easier, let’s simply divide humanity in two pools: one of females, and one of males. With every heterosexual contact, each pool gets a point. There is no other way, because a heterosexual contact always involves both a male and a female.

After a certain period of time, the average number of heterosexual contacts per individual can be calculated by dividing the total number of points of a pool by the number of individuals in that pool. The math is easy. Both pools have the same amount of points and both pools have the same amount of individuals. Ergo: the average male has just as many heterosexual contacts (and partners) as the average female.

The really interesting thing is why polls sometimes show otherwise. The first thing that comes to my mind is that for magazines it does not make an interesting headline if males and females are just as promiscuous.  Magazines might “interpret” the poll results  just to make an interesting headline.

Other things might play a role. Maybe some very promiscuous individual are excluded from the polls, for example  prostitutes. If males count their contacts with prostitutes, but the prostitutes do not participate in the poll, then the poll would say that males are more promiscuous than females.  Also other non-representative samples are thinkable. Maybe the readers of the magazine (=respondents to the poll) do not form a representative sample of the population.

Another source of bias can be in the minds of people. Maybe women remember more of their sexual partners. Males don’t count those they have forgotten about, maybe they were not important enough to remember. Such a thing would result in females giving a higher amount of sexual partners than males. Or maybe it is the other way around. Another thing might be that males count something to be sex, which females do not count to be sex. How far do you go before you call it sex?

Anyway: if polls show a difference between the promiscuity of males and females, then the conclusion that males or females (whatever the outcome was) are more promiscuous is false. The really interesting question is why such a difference is reported.


  1. don’t you think that if the MEDIAN for one one sex was very different than for the other, it would have meaningful implications vis-a-vis their respective promiscuity?

    Comment by kevin — December 11, 2008 @ 21:50 | Reply

  2. You’re using the mean as the average and what you say about the mean is clearly correct. However, it is the least illuminating of the averages. Suppose you had ten men and ten women. Each pairs up uniquely with one of the others. Then one of the women sleeps with all the other men as well. The mean says the women and the men both average 1.9 partners. The median and mode both say the women average 1 partner and the men 2. In this example the typical male is more promiscuous than the typical female and this is the information the polls are looking for.

    Comment by j — December 11, 2008 @ 22:08 | Reply

  3. Unfortunately it’s not that simple. Statistically, it is a well known fact that the average can be a very misleading figure, which can hide an awful lot of information about the distribution of e.g. sexual activity within the group.

    For instance, let’s say the definition of “promiscuous” is having more than 20 sexual partners. A few individuals can have a high volume of sexual activity as long as they are “compensated” by many individuals having an only slightly underpar volume, but there is no need for the opposite gender follow the same pattern. It then becomes possible for only one gender to have promiscuous individuals.

    You also incorrectly equate sexual activity with promiscuity. A monogamous couple is not promiscuous no matter how often they have sex. A person can be considered promiscuous without actually having that much sex, as long as they change partner every time. Consider a situation of ten men and ten women. If only one man has sex, but each time with a different woman, then yes the average is equal across both groups but clearly only that one male is promiscuous.

    With those basic principles established, it should then be easy to understand how it is mathematically possible for one gender to be, say, twice as likely to be promiscuous as the other. Add in various other factors e.g. variations of male/female ratios across geographies, different ages for starting sexual behaviour or getting married, different tendencies to cheat, etc, and it becomes clear that maths alone will not give you a clear answer to whether differences in promiscuity exist. From an evolutionary stand point, having a baby is far more costly to the female in terms of time. A male has reason to be promiscuous to spread his genes widely; a female has reason to be promiscuous to get the best genes, a separate matter to having a partner to raise the child with.

    So to really understand – you’re going to have to do polls. The really interesting question is how to conduct them.

    Comment by Jon — December 11, 2008 @ 22:11 | Reply

  4. @j

    > “In this example the typical male is more promiscuous than the typical female and this is the information the polls are looking for.”

    * In your example there is one very promiscuous male and the other males are less promiscuous than the females. Who is your typical male?


    > “You also incorrectly equate sexual activity with promiscuity”

    * My story is the same for counting sexual contacts and counting sexual partners. I thought about stating that explicitly, but it seemed so obvious that I decided that this needed no further explanation. I am sorry that you did not understand this.

    > “With those basic principles established, it should then be easy to understand how it is mathematically possible for one gender to be, say, twice as likely to be promiscuous as the other.”

    Let’s make an example. Thousand males, thousands females, an average number of sexual partners of 10 and someone is called “promiscuous” when the number of sexual partners is 20 or higher.

    Furthermore: to make it twice as likely to find a promiscuous male as to find a promiscuous female we need some chances that are interesting. Let’s say 40% for a male and 20% for a female – because “twice as likely” as in 1% and 2% is not interesting.

    400 males have 20 or more sexual partners, 200 females have 20 or more sexual partners.

    Because the average number of sexual partners is 10, it leaves 600 males with (10,000 – 8,000 =) maximally 2,000 sexual partners, when evenly divided among them, that is 3.333. For females it will be on average 7,5 sexual partners on average for the non-promiscuous individuals.

    The magazine goes polling this population and finds results as above. 40% of the males report 20 sexual partners, 20% of the females report 20 sexual partners. The rest of the males (60%) report on average 3.333 sexual partners and the rest of the females (80%) report on average 7.5 sexual partners.

    Now what would the magazine write as headline? “Males are twice as likely to be promiscuous” or “The median female has has twice as many sexual partners as the median male”. Both are true in this situation.

    My point: a “slightly underpar volume” for the majority does not result in a striking twice as bigger chance for one gender to be promiscuous. Of course you can pick 10% vs. 20% or even 1% vs. 2% to get this factor two, and the average numbers for the rest will be closer to the overall average. But then again, the smaller you pick those percentages, the less striking it is.

    Comment by takaita — December 12, 2008 @ 07:59 | Reply

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