The sex gap

By Razib Khan | April 22, 2013 4:14 am

I was recently reading Sexual Behavior in the United States: Results from a National Probability Sample of Men and Women Ages 14–94. At N ~ 6,000 it’s a large sample of American sexual behavior around 2010. There was one descriptive result which I thought was interesting, though not surprising. Before the age of 25 it seems that women are more likely to have sex in a given year than an equivalent age man. After the age of 25 this starts to reverse, and men are more likely to be having sexual intercourse in a given year. The dynamics underlying this phenomenon seem to be easily subject to various speculations, so I’ll leave that to readers. Rather, I offer the graph (data drawn from the paper linked above):


Comments (10)

  1. Georg Schoen


    on this were a lot more productive, if we knew the “true”

    figures along with the figures they got by interrogation. :=)

  2. JonFrum

    Divide the population into two groups – those waiting to become sexual, and those who have become sexually active. Statistically, the line would sit right about where this graph peaks. That is, if people are ever going to become sexual, it’s going to happen by their mid-20s.

    In those two age groups, you have different selection going on. In the early years, females can select the best deal for themselves, which is often an older male. Thus, for any yearly age cohort, sexual activity will be biased towards younger female/older male (although the difference will generally be small – one or two years).

    Once you reach the age where males catch up to females, and both sexes are fully sexually active, that bias goes away – males have equal opportunity to females. That explains the first half of the graph.

    The second half of the graph I take to me more complicated. Speculation warning: First, marriage locks in an older male-younger female equality of sexual behavior. If I”m five years older than my wife and we are monogamous, then our intercourse numbers will be equal. Second, I suspect that female interest in sex goes down faster than that of males. Third, given the opportunity, men of increasing age would keep having sex with 25 year olds for as long as they live. As a practical matter, this expresses itself in an ‘as young as possible’ bias that in practice is more like 5-10 years.

    My story – sticking to it.

    • razibkhan

      my model is similar. i put this post up because it seems to quantify what i’ve heard of/seen anecdotally. e.g., i have attractive (young looking) female friends in their mid-30s who are shocked all of a sudden how difficult it is to date because now they’re competing with women 10 years younger. to make things work they have to move up themselves to 45 year olds, and they’re not always willing to do so….

      the converse is that to some extent immature and broke 20 year old males compete for the same women with 25 and 30 year olds who have jobs and are more seasoned.

      • marcel proust

        Perhaps the women in their mid-30s should be dating the 20 year old men. My impression is that they make cheap dates (pizza anyone), and if the women are primarily interested in sex or showing off their vitality (which often seems to be the case when men date much younger women) it seems like a match made in heaven (especially if the women are more focused on quantity than quality of sex).

    • Great story. I would also assume that women, once they hit menopause, it affects their actual sex drives/hormones. This could play a role in why women fall off in the graph as they get older as they are less likely to continue to have sex due to the lack of hormones or lack of interest. They have already raised children and utilized the work of that uterus to its fullest extent so why bother if pleasure is minimal with increased age?

  3. chris_T_T

    I’m guessing at least some of the decline among females after 25 is related to children and single motherhood in particular. Single parents don’t have a lot of time for relations and a higher proportion are women.

  4. heressomeinfo

    I wonder if this includes gay sex. How much does that throw off the ratio? Gay sex counts twice for each gender remember.

  5. Street Anthropologist

    Mmmmm… Interesting! I can understand the sudden drop from 25-29. Maybe those women settled down and were preoccupied with child-rearing and household stuff and the men continued having sex maybe outside of marriage because their wives were busy and became homely).

    The most interesting, I think, is the rise among women aged 16-29. Is this related to the rise of sex addiction among women?

  6. Simple, older guys go after younger women. Younger women are easier to convince since they are eager to experience sex and are awed by money, looks and a ‘slick’ line. Older women want sex period, but with 25 year old men who have the endurance to satisfy their needs.

    But since men are always looking for younger women, the curve will always look the same.

  7. devdas5z

    I also wonder if the spike in men’s sexual activity relative to women indicates the point at which affairs become more common. When you get to the later years and most men and women are likely married, one would expect that monogamy would result in something close to a meeting of the lines, but instead men are finding more opportunities for sex.


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About Razib Khan

I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. In relation to nationality I'm a American Northwesterner, in politics I'm a reactionary, and as for religion I have none (I'm an atheist). If you want to know more, see the links at


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