the biology of human sex differences

In today’s New England Journal of Medicine, there appears an
article that describes the differences between boys and girls, for those physicians who skipped that lecture. Allow me to quote:

1. Fertility differs considerably between men and women. Men are
fertile from puberty through at least the 9th decade of life, and
some men are fertile into the 10th decade. Although there is some
decrease in fecundity, spermatogenesis is active throughout these years.

2. Women are fertile only for the 12 hours after the monthly
discharge of an egg from the dominant follicle in the ovary.

3. The other main difference between male and female fertility is the
rapacious apoptosis that occurs in ovarian follicles. Of the 3
million to 4 million follicles present at the time of fetal ovarian
differentiation, only a million or so persist at birth; 400,000 to
500,000 at menarche; and none beyond the sixth decade.

Men are fertile almost every minute of the time they spend on earth,
women are fertile 12 hours a month for 35 years, amounting to a grand
total of 30 weeks’ fertility over their entire lives. This fact
explains much of how men and women relate.

My sister Rachel has recently entered single adulthood and often
seeks my counsel on matters dating. I have discovered, while trying
to use my expertise in this area to optimize her love life, that
today’s woman is fucked.

I know this when I hear her describe her latest date, she’s so into
this guy she says, and he seems into her, but she’s not sure. She
describes him to me. Bright, successful, attractive, socially
intuitive, jewish. How much interest should she show? How much
cleavage should she show? How long does she have to wait to have sex
with him? Trying to answer these questions, I sense a sort of
futility to all the attention they’re paid, and it is the feeling of
futility that brings it into focus: Men and women want different
things, everyone knows that, but their discrepant goals are not
fairly distributed. The evolutionary expression of our biology sets
men and women in a Darwinian rivalry that women can not win.

A woman, if she becomes pregnant at every opportunity between
menarche and menopause, can have at most thirty or forty children. A
man can repopulate the world in a week. Is it therefore any wonder–
given that our instinctual purpose is to produce as many offspring
that survive to reproductive age as possible–that men seek variety
and women seek security?

Since women can have so few children, a woman maximizes her
evolutionary potential by assuring that each of her children is
offered the best individual chance of survival; it is thus in her
best interests to find a partner likely to effect an environment
where each child will survive to reproductive age. This instinct
manifests itself in modern society as the desire for a protector and
provider: a big strong rich man.

That man maximizes his evolutionary potential by impregnating as many
women as possible. Since there is essentially no limit to the number
of children physiology permits him to father, it is in his best
interest not to maximize survival of any one of his children but to
maximize his number of children. This instinct manifests itself in
modern society as the desire to fuck every woman on the planet.

These goals intersect at every encounter between a man and a woman.
While women channel their energies into finding and retaining a big
strong rich man, men are busy disseminating inseminating. The result
is that once a couple has sex, the man becomes more and more
valuable to the woman, while the woman becomes less and less valuable
to the man.

That sense of dread I have when Rachel describes this guy–I now know
exactly why she’s headed for a broken heart.

Related commentary from 2000 and 2004.

9 thoughts on “the biology of human sex differences

  1. Eric Carlisle

    Reub, certainly there are great examples of animal species where the males spend there lives trying to fuck every female on the planet; the elephant seal comes to mind as one such example. I believe the human male is a bit different though. In the vast majority of human cultures, men seem to run around for a few years trying to impregnate any willing and able body, but ultimately they find one or two women with whom to procreate, and commit the remainder of their fertile life with them. I would argue, based on this observation, that the nature of man is NOT to spend his time fucking every woman on the planet, but taking an active role in child-rearing in order to assure his children survive to contribute to the next generation. Since there are individual and cultural variances along this line of commitment, women are naturally discriminating and unbelievably good at weeding out the “players.” If your sister hasn’t learned this talent yet, I suspect she will very soon. Eric

  2. hugh

    The reproductive habits of mammals are divided into two main categories, K & r:

    “In order to maximize fitness in a predictable environment, it pays to invest resources in long-term development and long life (K selection); in a risky environment, it is better to produce as much offspring as quickly as possible (r selection).”
    http://pespmc1.vub.ac.be/RKSELECT.html

    Women pine after manly fuckers (say, Tommy Lee, Mick Jagger, Wilt Chamberlin) perhaps because manly fuckers have the sorts of genes that appeal to their r-selection instincts (which would be one reproductive option); as well as good fathers (who will provide good K-selection possibilities).

    And lots of women dump guys who are happy to be good fathers – perhaps because their genes don’t rate high enough to warrant wasting good ovaries on. and women often fuck jerks, or pretty idiots, just cause they want to get laid, particularly by “unsuitable” mates.

    point being, there is a balance for women as much as there is for men. it’s not all women with broken hearts out there, and lothario men.

  3. reuben

    thanks hugh for another newlywed perspective.

    interesting article, makes a lot of sense on an interspecies level but I’m talking about an intraspecies phenomenon here.

    also, you have slipped into an instance fallacy, which is to say that you can not refute a generalization with an instance. If I say black people have darker skin than white people, to show me a very dark white guy who is darker than the very light black guy standing next to him is not a valid refutation. of course there are women who seek variety (though many fewer, in my view, than the number who claim to be into caj sex) and men who seek security, but this does not address the issue.

    that men seek variety and women seek security I took as a given. if you don’t buy that, your experience as a single guy, if you can remember that far back, was very different than mine. the question I’m trying to answer why .

  4. hugh

    i don’t think it’s an instance to say women pine after sexy/unfatherly men, i think that’s a generalization. the curious thing is that they often project fatherly aspirations on clearly unsuitable men…interesting.

    but i’m not refuting, just pointing out that men do not *only* want to fuck every woman, and women do not want to make fathers of *every* man. tho that;s a general tendency, sure.

    but i would say both (subconsciously) want to optimize their genetic catch for whatever period of time necessary, often well beyond the first lay… the more prized the genes, the more intense the luvy-dove feeling. true for men as much as women. tho perhaps on a different time frame. and then there’s a balance between sexy genes and mating material, which do not necessarily coincide.

    by the way we are both going to feminist hell for this discussion, tho i’m hedging my bets better.

  5. Scout

    Rather than discussing whether Reuben can handle the idea of his sister sleeping with some random guy – which obviously he cannot…
    We should be discussing why violence against women continues to remain so manifest in all societies and on all levels.. From the simple jeer/catcall/abuse in the street, to violence in the home, discrimination, segregation, rape…
    There is something deeply wrong with a society in which the abuse, rape and murder of women are daily events.

  6. Jill J

    While it is true men can produce sperm well into their 100 year or beyond, their DNA breaks down and this DNA breakdown shows up in their sperm hence they are more likely to produce children with disorders. If they can produce children, which requires an erection and the ability to get that erection into a woman who is fertile not a mean feat for an old fart. By the way have you ever look at really old penis and testicles and the varicose veins, the sagging and the general lack of tone? Semi-Erect is still not erect to me. Men and women might not be the same, but old age sucks for everyone. Jill

  7. blogmonkey

    first time caller here.

    it seems futile to post a ‘I wholeheartedly agree’, but I will.

    I am happy that the ‘trap’ i am caught in at the moment, the biological pressure to dispense affections or ‘fuck the world’, is not brought on by megalomania nor perversion. having said that, as natural as these urges are, they are distracting, frustrating and extremely uncomfortable, to the point of utter despair.

    i would urge the ladies not to roll their eyes thinking that this is a problem that men enjoy, but an uncontrollable aspect of their nature that, unfortunately, plays against our western culture, media and progressive thought.

    we are meant to feel guilty for these leanings, which is unfair. it needs to be discussed and understood by the opposite sex, dealt with just as we have dealt with and accept their pms, obsession with toilet seats and the need to have their minds read and their insecurities coddled.

    to often, the harsh realities of masculine nature are met with critizism and the cocked brow of detractors who believe ‘we do it because we want to’, not because of nature’s decree. i’m all for greater understanding of the sexes, so long as it doesn’t mean the emasculation of men and ‘having fun’ at their biological tendencies.

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