Forbidden Fertility

Human conscious minds seem unaware of many important functions of human behaviors. Humans don’t know how they breathe, digest food, or stand without falling. But conscious attention is expensive, and there seems little to be gained from conscious minds managing such processes. Also, large system changes would be required to add control and sensory neurons in order to enable such conscious management.

However, humans also seem unaware of other important behaviors where more can be gained from conscious management, and where brains already seem to have something close to the required control and sensory connections. People don’t seem to know why they laugh, why they like the folks they like, or why they go to school or the doctor. Humans are unaware of their constant status moves, and are largely unaware of their overconfidence.

Now some argue that there is also little to be gained by conscious awareness of such things; the unconscious mind manages such things just fine. But if so, the conscious mind begins to look irrelevant; what should we expect the conscious mind to be aware of, if not such things?

One story is that consciousness is the mind’s public relations department, charged with managing our words and the actions we most coordination with our words, in order to present a good face to others. Given this theory, we should be surprised to see conscious minds unaware of things close to the content of their words, and to the actions their words coordinate.

For example, we should be surprised to see people unaware of their overconfidence, status moves, or tendency to mimic others to be liked. People vigorously deny the existence of such things, and are eager to explain suggestive evidence in other ways. Such unawareness seems better explained via motivation – it seems to be in our interest to remain unaware of such things, in order to present a more convincing face to others. Our minds may be designed to prevent conscious awareness of many such things.

One of our most puzzling unawareness is of fertility. In most primate species, female bodies clearly advertize when they are fertile, and males seem quite aware of such clues, which influence male plans and activities in big ways. Human female bodies, in contrast, do not so advertize, and human males and females say they are unaware of but the most obvious clues (e.g., discharges). In fact, the standard theory until recently was that there were no other such clues, that human female fertility is hidden. But in fact we’ve learned that not only are there many strong clues, both men and women are unconsciously quite aware of such clues, which strongly influence their behavior!

For example, a recent study paired random men and women for a few minutes. Even though “neither objective coders nor the participants themselves perceived any changes in the [female] confederate’s overt behavior across the menstrual cycle,” men were four times more likely (63% vs 15%) to mimic the woman when she was fertile:


Fertility is important, seemingly the sort of thing people would want to talk about and integrate with the actions that they coordinate closely with their words. Yet relative to other primates, humans have not only lost their big overt signs of fertility, our verbal selves seem completely unaware of other fertility clues, even as our actions strongly react to them! Why couldn’t men profitably talk about which women around them are fertile, and integrating such knowledge into their verbally coordinated plans? “George may not want to join us Saturday, as his girlfriend should be fertile then.”

Could motivated unawareness explain this?  Might it just look bad for men to attend to female fertility, so very bad that men have completely repressed their fertility knowledge, for fear of showing such attention? But men are usually eager to show their sexual sophistication; why the sudden eagerness to appear naive? What bad feature of a man could correlate so strongly with knowledge of fertility?

One possibility is that women want to keep their fertility info private, to give an advantage to men who are socially close to them, relative to distant men. They would then discourage public conversation on who is fertile when. But in this case close men would want to signal their closness to a woman via their knowledge of her fertility.

Another possibility is that a short term mating focus looks bad. Long term mates should be less concerned to discern fertility, if they expect to consistently mate over the entire fertility cycle. But men and women are both capable of and practice short term mating strategies, and both are often eager to signal their ability and inclination toward such strategies to desirable partners. If “cads” distinguish themselves from “dads” by acting rebellious and aggressive, why wouldn’t cads also distinguish themselves via fertility awareness?

A third possibility is that ancestral woman really disliked male mate guarding. Insecure possessive mates might tend to 1) guard females more, 2) attend more to female fertility to support such guarding, and 3) be less desirable as mates. Women would then avoid men who visibly attended to fertility. This correlation could apply to both short and long term mates; a woman might prefer a long term mate secure about her faithfulness, and a short term mate willing to leave peacefully when she is done with him.

This last theory supports Sex At Dawn‘s story of ancestoral promiscuity. But it also suggests that women now remain averse to men who show extra interest in their fertility cycle, and women just don’t report much aversion of this sort.

OK, I’m somewhat stumped – any other theories to consider?

More quote on fertility:

Subtle cues of fertility prime mating motivation in men, thus facilitating psychological and behavioral processes associated with the pursuit of a sexual partner. … Men exposed to the scent of a woman near peak levels of fertility displayed increased accessibility to sexual concepts. … In a face-to-face interaction, high levels of female fertility were associated with a greater tendency for men to make risky decisions and to behaviorally mimic a female partner. …

During the few days when conception risk is highest, for example, women report increases in sexual self-stimulation, overall sexual desire, and number of sexual fantasies. Women also report greater interest in activities associated with finding and attracting new romantic partners, such as attending social gatherings and wearing more sexually provocative clothing. During peak fertility, women show a particular preference for men displaying indicators of good genes …

Men tend to rate certain characteristics of women (e.g., their scent, their voice, their face) as most attractive during periods of peak fertility.  … Women report heightened mate-guarding behaviors (e.g., possessiveness and monopolization of the women’s time) by their male romantic partners during periods of peak fertility. … Female dancers received greater tips from men when near ovulation. …

Women, unlike the females of many other species, do not exhibit highly overt physical indicators of fertility, such as the sexual swellings that appear on the hindquarters of other primate females. Consequently, for quite some time, scientists presumed that women’s ovulation was concealed. However, an emerging body of evidence suggests otherwise. … Men subjectively evaluate the odors of women close to ovulation as more pleasant-smelling. … Shifts in women’s facial skin tone, vocal pitch, body symmetry, and waist-to-hip ratio have all been linked with shifting fertility levels.  …

The extent to which a woman’s fertility status elicits a man’s mating behavior may depend on the man’s orientation toward short-term versus long-term mating, whether the people are already committed to a long-term relationship, or the availability of other potential partners in the community. …

Neither participants nor objective coders noticed differences in the confederate’s behavior as a function of her fertility status, and participants rated her level of flirtation as quite low. … We suspect that men are not consciously aware of the degree to which their attraction is influenced by subtle fertility cues such as scent. (more)

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  • ShardPhoenix

    The idea that consciousness is *primarily* for deception doesn’t make sense to me – if that was true, humans would soon evolve to ignore (or at least strongly distrust) anything that seemed to come from another consciousness. Of course deception does seem to be one of it’s effects, but to be credible it must be honest much more often than not.

  • Marcus

    Another possibility is that intellectual understanding of the costs of families required the advertising to go underground. Actually seems to stand up pretty well as an idea against those other more complicated theories.

    • “Another possibility is that intellectual understanding of the costs of families required the advertising to go underground.”

      This is a more elegant explanation than the others. Hanson responded, “Marcus, it seems much simpler to just add a preference for kids.”

      Is Hanson saying that overcoming the effect of intellectual understanding could be more straightforwardly countered by evolving a preference for kids, rather than underground advertising? The problem with that reasoning is that conflicting conscious preferences are costly in themselves.

    • I’m also with Marcus…

      On the one hand we have an instinct which lead us to compete against other individuals (to acquire assets, success etc) – so as to advertise fitness to females. On the other, we have an instinct to raise kids. But that’s time consuming and costly – and it’s hard to achieve great things while doing it. So presumably (and it seems intuitively right) – the achievement instinct shuts down once a male is ensconced in a reliable relationship.

      But the two don’t cohere particularly well. Kids tend to get in the way of building castles in the sky. And a man that consciously believed that he wanted kids would probably also reason that he wasn’t that interested in achieving great things. Such a man would be less motivated to achieve such greatness and would therefore appear as less of a catch if that instinct took over before a female had been acquired.

      So how could you solve this problem? How could you be maximally motivated to achieve great things so as to advertise fitness to females, and yet not cock block yourself from mating out of unchecked ambition? Hide the fact that all you really want to do is get laid. Hide the fact that you are tuning yourself to the women around you. That way you can retain the belief in your own ambition (your desire for grand castles), and yet still navigate yourself toward raising children.

      Kinda explains male mid-life crises… they get duped by their primal behaviours into raising kids and once that’s done they realise their ambition component has been left unsatisfied.

  • David

    I’m inclined to think that the conscious mind is best at dealing with a small number of strong signals. Processing a large number of weak (relative to noise) signals – eg detecting subtle cues of fertility – seems to be a strength of the unconscious, or intuition, or ‘gut feeling.’

    Maybe the conscious (verbal?) mind is the ‘spherical cow’ module of the brain, taking a small set of strong pieces of evidence and constructing a resultant worldview. The unconscious is responsible for the statistical task of aggregating a large body of weak evidence. But if the unconscious is relatively confident of its conclusion (as the strength of the mimicry curve would suggest), why can’t it feed this information to the conscious mind – ‘hey, she’s fertile’?

    Perhaps one could extend from analysis to action – the conscious mind handles a small number of ‘ strong’ actions – such as saying, ‘you look fertile, wanna shag?’ (This rarely works.) The unconscious handles large numbers of individually ‘weak’ actions, ie body language, laughter, other social cues. So the unconscious input module detecting fertility, routs directly to the unconscious output module trying to socialize. All it send to the conscious mind is, ‘hey, she seems nice, keep talking.’ This presumably ties back to the ‘expense’ of conscious attention.

    • JAMayes

      Whoops, that was supposed to be a reply.

      But if the unconscious is relatively confident of its conclusion (as the strength of the mimicry curve would suggest), why can’t it feed this information to the conscious mind – ‘hey, she’s fertile’?

      Doesn’t it though? The mimicry may be unconscious, but I’ll bet men consciously “feel” more attraction to fertile women. That would be consistent with the study showing that strippers make more tips when they’re ovulating. The unconscious is sending the signal to the conscious, it’s just not using the word.

  • JAMayes

    But if the unconscious is relatively confident of its conclusion (as the strength of the mimicry curve would suggest), why can’t it feed this information to the conscious mind – ‘hey, she’s fertile’?

    Doesn’t it though? The mimicry may be unconscious, but I’ll bet men consciously “feel” more attraction to fertile women. That would be consistent with the study showing that strippers make more tips when they’re ovulating. The unconscious is sending the signal to the conscious, it’s just not using the word.

  • Doug

    Seems possibly tied to the fact that the first thing almost all civilizations are concerned about are 1) enforcing sexual monogamy and 2) closely tracking the calendar.

    Those making large investments in agriculture need to be jealous mate guards against nomadic cavemen badboys, and Stonehenge allows them to be aware of their females’ fertility cycles without making them look like neolithic creeps.

  • Pablo Stafforini

    Robin, human sexuality as a whole is unmediated by conscious reflection. Our ability to respond to signs of ovulation seems no different from our ability to respond to other signs of fertility, such as facial symmetry or a certain waist-to-hip ratio. These other signs are also unavailable to consciousness (we don’t feel attracted to women who exhibit such other signs because we take them to be markers of fertility; we just feel an urge to mate with them, and act accordingly). As far as I can see, the results you cite raise no special puzzle.

  • Pablo Stafforini

    (Minor correction: facial symmetry is a sign of genetic quality, not [as far as I know] a sign of fertility.)

  • Shard, the hypothesis was “to present a good face to others”, not to deceive.
    Marcus, it seems much simpler to just add a preference for kids.
    David, the unconscious could collect weak signals into a total clue given to the conscious mind. This happens all the time.
    JAMayes, if the clue were about a monthly cycle rather than a momentary feeling, we could plan ahead over the next month or so.
    Doug, be interesting to see evidence on farmers tracking tracking monthly cycles.
    Pablo, it is harder to see the use of consciously knowing exactly why a woman looks sexy. It is easier to see the practical value of tracking monthly cycles.

    • JAMayes

      Intuitively, I don’t see why that sort of planning have been particularly useful to male hunter gatherers. Would the tribe have given a male member the day off from hunting because his mate was fertile? It’s not like mating is a full day event.

      • Hunting trips can often take several days or longer.

    • JAMayes

      To me, that cuts the other way. Would a successful tribe allow males to skip out on multi-day hunting trips just because their mates will be fertile during the period? Making sure the tribe procures sufficient food would seem more important to genetic survival than catching one of a particular female’s numerous fertile periods.

  • Khoth

    These days, conscious knowledge of fertility is mostly used to avoid having children rather than to assist it. Perhaps this isn’t a new trend.

  • Dave

    These types of studies and many others sited here are like studies supporting mental telepathy. They never go anywhere over time,say for example over a several year period.So a body of knowledge never accumulates.So the jury is always out.
    No countervailing,confirmatory or clarifying studies are produced but in medical studies of ,say the efficacy of a drug or treatment it takes years to sort things out and there often negative studies. Only counter intuitive stuff is discussed because it is so amazing. I could never tell if my wife was fertile even getting really up close.So you are saying guys in a room or in a strip joint can tell,unconsciously? If there is an effect, how do you know that the ques are not based on the way the woman acts rather than subliminal stuff? I suspect publication bias.

  • OhioStater

    I’ll propose a simple answer: the women with open fertility didn’t mate with high quality men and their offspring died off.

    Women with quiet fertility mated with the best men and their offspring thrived.

    • Doug S.

      And high unemployment is caused by too many people being out of work…

      • OhioStater

        Technically it is. If I’m out of work, I can’t buy goods or services from your firm, and then you lose your job. I can’t wait for the day when robots do all of the work.

      • That’s positive feedback for you.

  • agnostic discusses his awareness of female fertility cues all the time.

  • In a classic OB post, The cognitive architecture of bias, Jason Weeden laid out the public relations theory of consciousness.

  • ShardPhoenix

    Robin: Selective publication/omission of one’s traits is fairly comparable to overt lying, so the same objection holds.

  • ShardPhoenix

    “Marcus, it seems much simpler to just add a preference for kids.”

    Also, I don’t see that this is necessarily true. I don’t know that selection is likely to directly genetically encode a preference for some so complicated, rather than indirectly (which already happens).

    In fact, simply turning off pre-existing abilities seems far evolutionarily simpler than building entire new ones from scratch.

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  • erik

    robin says he’s stumped about hidden fertility, but there are many published theories of it.

    something like a combination of the three possibilities he mentions is pretty well accepted: continual female receptivity to non-reproductive sex promotes pair bonding and encourages men to stick around for the meat-for-sex trade even once the kid is born and the woman is lactationally amenorrheic. keep in mind that pre-modern-era women almost never ovulate, they are almost always pregnant or amenorrheic; if the male is prevented from knowing when the small window of opportunity occurs for a subsequent conception, he is encouraged to commit for the long term.

    this is a big enough improvement in the kids’ survival probability to overcome an improvement in male fitness from losing interest in temporarily infertile women. moreover, hidden fertility makes the male more secure against cuckoldry, and he would be more likely to choose cooperative relationships with men more oblivious to fertility.

    robin is skeptical because 1) “close men would want to signal their closness to a woman via their knowledge of her fertility”, 2) sometimes both genders advertise a desire for short term mating, and 3) women don’t report aversion to male interest in their cycle.

    but, 1) women select AGAINST awareness, so it is in a male’s interest to not signal awareness, 2) why should we take advertisements for desire of short-term mating at face value?, 3) why should the aversion be conscious? many of our attractions/aversions are not. moreover, if male awareness practically never occurs, ongoing maintenance of an aversion to it would fail.

    interestingly, it is thought that humans lost most of their olfactory receptors due to women selecting mates that couldn’t discern fertility.

    off-topic: i’d like to see a post addressing whether modern society humans are post-evolutionary, to the extent that heritable phenotype has almost no relation to expected number of offspring. also, what are the evolutionary advantages of programmed senescence and menopause? starting points for this one:

  • erik

    come to think of it, are women not typically averse to the intense physical inspection that males tend to enjoy?

  • Jim Ancona

    WRT our lack of conscious self-awareness of many things, I’m reminded of a line I heard when I was in the enterprise software business, “Don’t tell the salesmen too much, they’re much more effective when they don’t know they’re lying.”

    If the conscious mind is the salesman, then lack of awareness probably makes deception more effective.

    A similar argument might apply to men’s lack of conscious awareness of female fertility. If you believe in “selfish genes,” then it’s always in male genes’ interest to impregnate a female, as opposed to the female case, where long gestation and child rearing time argues for quality over quantity. Given that, from the genes’ perspective, all the conscious mind can do is screw things up, by deciding that it doesn’t want to get this particular female pregnant at this time. So the genes make sure the conscious mind doesn’t have the information available.

  • Is the system in equilibrium? If relatively concealed ovulation and unconscious knowledge are the current states of an “arms race” between men and women, it could be argued that men have not kept up with changes in women. The ability to consciously know might evolve over the longer-term, assuming women don’t in turn improve their concealment.

  • mjgeddes

    The function of consciousness is to integrate the behaviour of conflicting sub-agents and form a coherent unified representation of our goals via narrative. ‘Presenting a good face’ (public relations) has got nothing to do with it (or at best, it’s only secondary usage).

    As to Bayes, that’s just the mechanics of intelligence, it doesn’t even scratch the surface of the true core of intelligence. It’s been decades since the Bayesian revolution but do you see a whole group of Bayesian statisticians suddenly winning Nobel prizes and making great scientific breakthroughs everywhere? Of course not.

    Sorry, you ‘Less Wrongers’ , Sing Insters and FHIers really have proved useless. I’m having to solve the whole Singularity-thing single-handedly at this point.

  • Khoth and Jim, it would be bizzare if anti-fertility preferences had persisted a million years.

    erik, the question is how women select against awareness.

    Josh, that isn’t a theory of male unawareness.

  • At least in the interest of making the discussion more focused, I’m still a subscriber to the theory that “consciousness” is a side-effect from the way the brain stores memories. It doesn’t require any special events to happen for it to appear and is consistent with the way we experience consciousness.

    That said, to the more general point of this post, I’d suggest that we aren’t conscious of those things that have not had a benefit from us being conscious of them, that is, creating concrete memories of the particular details of interest. We aren’t conscious of female fertility because there was not (and probably still is not) a strong selection pressure to cause those who do notice it to reproduce more successfully, thus in the general population the details of female fertility signs are not noticed because there has been no reproductive benefit to remembering them (and thus able to notice them).

  • Very interesting. Something to consider is that our overall fertility health is not as good, and this may contribute. Now 25% of couples trying to conceive are not easily able to. There are some basic things to pay attention to to improve signs of ovulation (our most fertile time), as well as our general health. These include healthy digestion, normal blood sugar, and managing stress. Maybe these are factors.