What would be the most important consequence of decreasing sexual dimorphism in humans?

Question

Related to this question on lack of human dimorphism, but hopefully the length of time my question has sat in the sandbox unremarked means that I have successfully been more specific.

I'm writing into an old shared universe in which the use of the words "male" and "female" are so absurdly stereotyped that it reads poorly in this day and age. In order to mitigate this, I have decided that in the context of the part of the world I'm building, these words indicate separate subspecies of humanity, not biological sex. Therefore, I have created the following:

Imagine a race very like humankind that has such a low degree of sexual dimorphism that males and females are indistinguishable from one another in day-to-day life. An individual's sex can be readily determined by even a cursory inspection of the genitals, but no other single physical attribute is a certain link to sex. The breasts have been internalized. Other physical characteristics have also been regulated and normalized to some degree, so most everyone has roughly the same skin tones, eye colours, hair colour and texture, etc. Also, most everyone is pretty broad and husky; the hips are about the same shape for everyone, and pregnancy isn't very obvious except in the very latest part of the term, and even then is only readily detectable when an examinee is unclothed.

A few generations ago, this population was isolated and genetically re-engineered from human stock to be this way, so I already have a plausible backstory justifying how this came to pass. This state of affairs isn't a shock to any of these people; they were isolated when they were re-engineered, so they never knew what it was like to be able to differentiate between the sexes and it doesn't strike them as at all odd.

Their environment, to which they are physically constrained, is rural and temperate, with very little seasonal variation (I'm aware that I need seasons for many kinds of agriculture, but I'm not going to sweat that). This requires that fairly heavy clothing be worn year-round. Their society is agrarian with touches of hunter-gatherer, and very loosely based on the dark ages in terms of technology. Importantly, I have already decided that an individual's sex is a subject of deep privacy, and speculating with any degree of publicity about someone's sex is one of the deepest taboos.

Of course, this has had an enormous impact on their society. Sexual discrimination is all but non-existent (instead, people tend to discriminate on the basis of sub-species, but that's another story). Social roles that we might recognize as being gender roles are apparent (eg. that person goes out to work the fields, and their partner instructs the children), but are for convenience only and are largely not tied to biological sex. Language has evolved into a gender-neutral dialect; although a few ancient legends have survived which speak of male or female characteristics, it's generally understood that these stories are clearly written about gods or demi-humans, and are not to be compared with current society. A few individuals have dissented against this interpretation, but they have historically left this society to live on their own in the wilderness.

Given all this, what's the most important consequence of this change that I have overlooked?

EDIT: Genetic diversity isn't an issue. The process of the genetic re-engineering has eliminated genetic diseases. It bears mentioning, I suppose, that the story is only a few generations into their exile; long enough that the origins of their incarceration are now distant legends, but not long enough that the consequences of the small initial population have really started to show.

EDIT 2: I guess I wasn't explicit enough, my bad. The feeling for this subrace is one of extreme social conservatism. Think of the Puritans, perhaps, and the comparison with Pratchett's Discworld dwarfs is well-founded.

Answer 1

Bouncing a little bit off of jstewart's answer, and the potential of attraction being gender neutral in this setting for that reason, I think one potential consequence might be the more frequent or more acceptable formation of triads and foursquares or negotiated arrangements about childbearing.

Courtship is likely to be a long and delicate process, given the gender taboo - and it isn't impossible, or honestly even unlikely, that people might fall in love irregardless of gender compatibility, maybe even before knowing. If people are encouraged to have kids, or want them, or have better lives with them (for social reasons, or economic ones, or whatever) - then a couple who are not compatible in that way might break up to try to find a compatible gender... or they might stay together and go looking for an arrangement.

So, they might, very quietly, let a mention that they are looking for reproductive assistance loose among their closest friends and family (who might already know their gender, or not). Such and admittance doesn't even have to admit that they are the same gender, since fertility or even sexual issues might be fixed in the same manner. In this way, through safe and private social networks, those looking for such assistance in reproductive matters might meet, gently feel each other out, and come to an agreement - to check gender compatibility (or whatever), and try for children - with said children being split between the individuals directly involved (so two couples, or one couple and one single parent each get one or more kids), or possibly raised in the three- or four- group communally.

Again, the only thing that might get out is the couple's potential need for a third - not what gender each is, not if gender or other factors were the original issue, they would only be revealing what gender they are looking for to a few more people, who would be equally exposed. With a fifty percent chance of finding someone the right gender the first time (well, second time per individual, first time per couple) and maybe fifty percent of the population already having found a mixed gender pairing the first time - three quarters of the population with relationships viable for reproducing with just one or two tries is much more sustainable, especially since those really interested can keep trying until someone is found.

Not really violating the taboo this way, I would think - especially since telling what gender they're looking for (especially as a couple) doesn't precisely disclose both their genders, only that one of the two is the (probably fertile) opposite - a mixed couple with fertility issues would be seeking the same way. Though future kids are more likely to get created through the already formed negotiation, since that would be easier than negotiating to check gender all over again - so stable relationships and semi=relationships are more likely to form.

Threesomes and moresomes are not common in sex- or gender- conservative societies, true - but this kind of only-for-children extra relationship isn't unheard of, especially among those favoring their own gender or who had fertility issues, who might go looking for someone to reproduce with without sacrificing their other relationships - some cultures allowed surrogacy or official alternates (like mistresses) for just that reason. And in this society, with no social pressure driving them apart (because no one knows their genders), but a social pressure to reproduce that about half to population can't meet any other way - I expect such relationships will be kept discreetly quiet, but pop up commonly enough to not be remarkable. And knowing that one male and one female must exist in a group of three or four is much harder to figure out specific people's genders than a group of two.

The only other possible alternative is for certain classes of people (perhaps those of certain ages) to be relatively indiscriminate in their partners for a while (equivalent to dating, okay), so that people would find those of both genders over several relationships, and would already be "in the know" about a number of people when it came time to consider reproduction. The downside to this is that it will strain, and eventually break, your taboo - roughly equating gender-reveal to sex, this is the difference between a less repressed culture where premarital sex or multiple sequential marriages are expected (knowing the genders of all the people dated) and a much stricter culture where it is strictly forbidden (only knowing the gender of the person married), which seems to be what you were going for.

Answer 2

So, we've already considered the problem of people of opposite sexes trying to identify each in order to agree to mate, but I think there's a problem here that goes deeper than just identifying the sexes of people.

To give a concise summary title:

What turns you on?

Disclaimer: I'm not a biologist, so there could be facts I'm missing, and biologists can correct me if so.

More specifically, I don't think that sexual attraction is precise enough to reward only reproductively viable sex without gender cues.

My hypothesis would be that the reward mechanism for sex isn't actually able to distinguish reproductive sex from any other sexual activity in the presence of a partner that one is attracted to. That is, it is set up to:

1. reward any sexual activity, but
2. reward sexual activity with (or in proximity to?) a partner, of the sex you are attracted to, more.

As evidence of this, I would point out that we know that heterosexual couples in our world now engage in sexual activities that are not reproductively viable.

If it is true that sex drive is only based on the combination of sex-specific attraction and sexual activity, then there are a few problems you might have, depending on how sexual attraction works.

No attraction

Since the sexes are nigh-indistinguishable, nobody is attracted to anybody else. Sexual activity may still be rewarded, but there's little motivation to find a partner because the mutual sexual activity part doesn't work. Reproduction becomes a chore. Later generations wonder why anyone would bother with the trouble of raising kids, and the species or subspecies quickly goes into decline.

Everyone is attractive

Everyone is effectively bisexual and can get their extra mutual-sexual-activity reward by associating with anyone of either gender. I haven't rigorously done the probability math, but I think you end up averaging either exactly or close to half of couples are same-sex. Now all of the couples which are by coincidence heterosexual have to produce twice as many children to keep the population up.

Since the average number of children per family needs to be at least two, and half of families will produce none, that means that the heterosexual half of all partnerships needs to average four children. And if you don't assume modern medicine, that number will be much higher. If an average of half of all children die from disease, that means that those couples have to have an average of 16 children, which could be a huge economic burden, if nothing else.

There are ways around that problem, to some extent.

One option would be to culturally preference heterosexual relations. The problem here is that no one can really check -- you can't argue the difference of whether partners are of different sexes vs just not successful at conceiving a child without violating the taboo on discussing someone's sex. And if no one can check, some people will prefer relations with someone of the same sex who they're already close to over going out to find a partner of the appropriate sex. This is especially true if it takes a long time to get close enough relations to find out someone's sex. It also means that if children are an economic burden, then some partners who are of opposite sexes might still not bother having children.

If they're agrarian, then it may be that they are motivated to have children (and thus find opposite-sex partners) for economic reasons: free farm labor. That depends on costs of raising children compared to hiring labor. If you can get labor just in exchange for food, well, children may require less food than an adult, but they also have several years where they consume food without being able to work, followed by several years of being weaker (and therefore worth less as laborers) than adults, so I'm not convinced that this would be sufficient motivation.

They could just have adoption to even out the children being raised by families, this works especially well if they're engineered so that both sexes can lactate. The partners who are of opposite sexes still have to produce more children, but at least they don't have to raise more children.

Super Attractive Genitalia

It's the only part that's definitely distinct between the sexes, so their attraction could be based on that instead, which would only give the extra partner-sex-reward for the correct sex. This still has issues.

First, it will have to take a long time for a relation ship to develop before you can tell the partner's sex, which means you have to expend a lot of energy forming a relationship before you even know if your partner is attractive to you. This is going to put strain on society and maybe motivate some rebellious youth towards reducing the secrecy of everyone's sex.

The other problem is that part of what motivates people to actually have sex is the fact that merely being in the presence of (or seeing) someone of the sex you are attracted to is enough to... trigger certain biological responses... I think this is a combination of built-in programming to respond to the distinguishing features of the sex you are attracted to and conditioned responses, often developed from cultural norms that you associate with that sex. If you can't tell the sex of the other person by sight (or smell, or voice), you can't tell if they're attractive, and you won't be motivated to proceed.

There are some other variations this could have, like being attracted to everyone until you find out their sex, which could work, but also put a social pressure in favor of revealing your sex ahead of time, since it's a lot of trouble to build up a relationship just to find out you're not attracted to the other person -- you have the normal stress of relationship uncertainty, but with the added bonus that you'll have a 50% chance on average of your relationship ending immediately or reverting to friendship the first time you reveal your sex, one way or another.

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And of course you can't just have attraction to some people and not others (maybe by pheromones?) since then you could tell someone's sex just by standing close enough to them and seeing if you find them attractive at all.

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Conclusion (& tl;dr)

All in all I think that unifying traits too much would make a huge mess of courtship -- not just in that it will be difficult to find a partner of the right sex, but in that it will make even triggering the sexual attraction response more difficult, possibly to the point of making sexual reproduction nonviable, and giving the species immediate negative population growth.

If you really want to have sexual reproduction without having distinct sexes, and you're willing to go so far as to genetically re-engineer the entire population in question anyway, why not just make the whole population reproductively-functional hermaphrodites?

Answer 3

How do they have kids??

Say a member of this species wants to have children. He knows his gender but now he needs to find a female to mate with. There are no real visual clues about who is female. Since "an individual's sex is a subject of deep privacy" he can't really ask. Even if he knows some one who is female who might mate with him, she can't find out he is male either so neither knows and neither can ask.

Finding mates of a particular gender becomes a hard coordination problem without visual clues. This is why humans have established visual clues for male/female interested in male/female.

This would make it very hard for mates to find each other and would make having children harder and rarer.

The social stigma of pregnancy, you mention that pregnancy is not really visible till the very latest part of the term, but it is slightly visible. Since showing gender is taboo showing pregnancy or saying you had a kid would also be stigmatized.

The risk of mating

If two beings mate and produce children they implicitly say that they are different genders, so if a third party knew the gender of one he would learn the gender of the other. This might lead to secret relationships.

Answer 4

Ok; so assuming the problems of birthing and so forth are resolved (somehow). Then they should have a much longer lifespan relative to the raising of children than humans do, and be able to have children for a much longer time. Basically if both parents are involved in the raising of children to the point of limiting the work they do for the period of time of child birth and nursing (there needs to be extreme social stigma regarding the non-pregnant part of the pair leaving during that time period as doing so lets out who is of what sex (besides all the other problems)) then that limits the number of children that can be had, suggesting that it would be desirable to have a very few children at one time (one pregnancy or two back to back) and then go a longer period of time without children before having more; as replacement in modern medicine industrialized society is about 2-3 children per women and it was significantly higher in pre-industrialized society that requires much longer time that they are able to have children. Changing how often and when the females are fertile could help, if they are only fertile once or twice a year not getting pregnant becomes much easier (it also makes it significantly easier to hide that one is a female if one is only menstruating once or twice a year).

I would suggest that with the longer lifespan it is possible that marriages could becomes less permanent, one marries, has a kid or two (or not) and then seven-ten-ish years later separate with the sex of ones prior partner being absolutely taboo to disclose. Based on past societies there may be the social expectation that some of ones unions do produce children, but lowering the infant mortality rate significantly below what did exist could lessen that social pressure.

Obviously, there isn't a gendered component to inheritance laws, but it would be entirely reasonable to have, at some point prior to death, the parents provide as they are able an amount of capital, be it land, a house, or money to help their offspring get established.

Answer 5

The most logical way for a species like this to be viable is if childbirth is more evenly divided between the parents, or among the community. The main reason why the sexes are distinct in the first place, both biologically and culturally, is because childbirth is hard for the female, but not for the male. For humans even more than most animals. Producing a child means that the woman is going to spend several months less mobile (making it harder to collect food) as well as requiring additional food to feed the developing child. This burden continues after childbirth, since it is the woman who nurses the child. This means that, especially in a natural, pre-civilization environment, there will be more pressure on the woman to avoid producing a child until she can find a man to help provide during this difficult period. The culture develops around those assumptions. It's less of an issue in a civilized society where food is abundant, but it's still an issue unless the government steps in with laws like maternity leave, even so many women find it difficult to raise a child and work at the same time.

To create a humanoid species where sexual dimorphism is virtually nonexistent, I would make two main biological changes: have the child born much smaller (like bears, or even marsupials), and allow both sexes to produce milk (not too far-fetched, as a simple mutation is all it takes for a human male to produce milk). They may have evolved from a sexually communal species similar to bonobos, which already have less sexual dimorphism than most apes. I would expect the species to evolve in an environment with abundant resources, where competition between individuals is less important.

Basically members of this species all have sex with everyone and giving birth is a fairly simple affair that happens sometimes - since birth is easy, there would be no reason to avoid having a child. The baby would be born completely helpless and be raised by the entire community, spreading the burden to everyone. The drawback to this system is that, although the burden of childbirth is lifted from the one who actually gives birth, it would take a longer time for the child to grow and be a fairly big investment for the whole community to raise. It is therefore possible that babies of this species might not be considered people until they reach a particular stage of development; if the community was not ready to raise a new baby they would just discard it.

Answer 6

The most important part of the change that you overlooked is that male and female brains are different. Without stepping into the culture wars landmine that is the sex vs. gender debate, let me just say there are anatomical differences in certain brain structures.

For some specific examples: it appears that emotions are controlled in different parts of the ventromedial prefrontal cortex for men and women, there are neurochemical differences in the hippocampus that may affect the ability to think while under stress, and there are conflicting findings over whether inter-hemisphere connectivity is different between men and women.

Trying to ascribe psychological differences to these physiological differences is a bridge to far for me, a non-neuroscientist, but this suggests to me that the reason men and women seem to act differently, in my experience, is that their brains are wired differently, so to speak.

The practical effect of this on your society is that if the external physical changes were removed, and even if the societal obligations (child-rearing vs. going out to the fields) are changed, there would still be the not-obvious psychological differences between the men and women. That is to say, someone who is a human being and used to interacting with both men and women, should be able to tell the difference between a man and a woman just by talking to them.

Answer 7

So both genders would need to have wide swaying hips as otherwise the death rate of babies would be much higher than it already was and your society wouldn't last too long. This would lessen the power of those working the fields and hunting, which would be disadvantageous to a society.

Even if other sexual dimorphism goes away it would be incredibly hard, especially in a preindustrial society, for the gender roles to go away completely. Females are the ones that have babies. This means that they can not be depended for their muscle power especially without modern medicine as the childhood mortality rate (and maternal death rate) would necessitate frequent pregnancies (assuming the technology to not get pregnant existed in a reliable form). Then once a baby is born the females still could not work for the first two years (at least, longer is better in such a society) as they need to be nursing (though I suppose both genders having rather than not the easy ability to nurse would be better regarding the survival of children and thus society). Even once the children are weened they still would require near constant supervision and limited ability to contribute, which necessitates that someone take care of them; by assigning the role of that someone to those who are already required to bear and nurse other children one frees up more labor for farming and hunting.

Basically everyone would look like girls do hurting the productivity of a pre-industrial society greatly and married women would still have the pre-industrial gender roles of cooking, spinning cloth (not at all a trivial thing), and caring for children while married men would continue to work the fields or hunt. Even if you went further and said that either gender can have children and nurse splitting the responsibilities would still be the logical thing to do, though switching off who was pregnant and nursing and staying home might be appreciated.

In an industrialized society things do change quite a lot, and in a futuristic society that has artificial wombs and other technologies the gender roles could become largely irrelevant.