Worldbuilding Magazine: Xenobiological Determinism



Volume 3 / Issue 3 : Gender & Relationships- Visit their site to read the full issue


Xenobiological Determinism

Cathy, the Overprepared GM

In 1969, Ursula K. LeGuin published the landmark novel, The Left Hand of Darkness. The protagonist is a human diplomat living in a world of very human-like aliens. Unlike us, however, they’re androgynes who develop sexual characteristics only when they’re in their equivalent of heat or rut. Crucially, LeGuin explored how this biological difference would influence the aliens’ culture. Her book examines the links between sex and gender, as well as between biology, society, and culture. The book was a revelation. It fueled a wave of feminist, sci-fi, and sociological thought experiments that continue to this day.

One strain of this discourse leads to examinations of human gender in works like Margaret Atwood’s feminist dystopia, The Handmaid’s Tale, or the investigative thriller Orphan Black. However, another strain of science fiction focuses on creating sentient species with different reproductive biology and exploring the societies which could arise as a result. For example, in her Xenogenesis series, Octavia Butler imagines a race of Oankali who have three sexes—male, female, and ooloi. The ooloi can manipulate genetic material and are biologically compelled to interbreed in this way with other species rather than reproduce with their own species. As another example, in The Books of the Raksura series, Martha Wells imagines a fantasy world where two species, Aeriat flyers and Abora climbers, have merged to create a culture with six genders. Their society lacks the concepts of heterosexuality, monogamy, and chastity, although they do have firm, yet non-human, gender roles.

If we want to do something similar as worldbuilders and create a new species whose differing reproductive biology results in very different societies, we should first start by understanding what options exist in terms of reproduction.

Sexual Reproduction

Humans have two biological sexes necessary for procreation. Across all human cultures, this distinction between male and female is important, which is why societies develop the concept of gender. Now, each society conceptualizes gender differently. Many have two genders, while others recognize three or more. Gender roles may be tight or loose, and the roles themselves may differ from society to society. However, if we change the number of sexes necessary for reproduction, we can create cultures with greatly different concepts of gender and relationships.

Asexual reproduction is uncommon in multicellular organisms. Scientists think it may be more beneficial in extremely stable environments, but sexual reproduction is generally more useful in changing environments because it promotes greater diversity. So, we could imagine a complex asexual species that mutates and gains diversity in other ways—perhaps through an ability to more actively control their genetic inheritance or perhaps through a symbiotic virus that transfers genetic material among species. Such a species would have no concept of gender at all, and probably no need for romantic relationships or anything similar. However, their tribalism may be even stronger than that of humans because they don’t have our intrinsic need to mate outside of family.

Hermaphrodites would probably also not develop genders as we know them; however, they would still have sexual reproduction, so they may very well develop the concept of romantic relationships. Most corals, earthworms, slugs, and snails are hermaphroditic, as are many flowering plants. One interesting twist is that not all hermaphroditic species have all sexual characteristics at the same time. For example, some may be biologically male or female depending on the environment. They may switch from one to the other if all the community members are currently expressing the same sex. Among species that do this (for example, clown fish, parrot fish, goby, and wrasse), it’s often the largest or most dominant member that switches, although whether the switch goes from male to female or female to male depends on the species. Alternatively, we could imagine hermaphroditic species who change sexual expression as part of their life cycles. So for example, they may be neuter as a youngling, then become male as an adult, and then transition to female in old age (or some other ordering). In this case, gender and age/cohort concepts may be intertwined in a way they aren’t with humans. Inheritance in this case might be a little different with matrilineal societies being the default.

More reproductive sexes are also theoretically possible. Two reproductive sexes make sense on earth because we have double helix DNA, so each parent can contribute one strand. However, the alien equivalent of DNA might follow very different patterns. Perhaps they could have something like a triple helix design with three strands of a DNA analog, in which case they could have three or more sexes. In this case, I could imagine that they would still develop a concept of gender, but their understanding of genders would probably assume a trichotomy rather than a dichotomy. Presumably, relationships would revolve around triples rather than couples, although I could also imagine a situation where there are stable couples and a promiscuous third sex.

Neuter sexes would also significantly affect the development of the concept of gender. Many human societies develop the idea of a third gender to describe people who don’t neatly fit into the pattern of one of the two primary genders. However, if there were a true neuter sex that was not involved in reproduction (for example, worker ants), then it would redefine the other genders by their contrast with the neuter, rather than solely by their contrast with each other. In some ways, both reproductive sexes would be in contrast to the neuter sex. Evolutionarily, neuters would be predisposed to help their siblings’ families in the same way mothers and fathers do their children. If the species develops clear gender roles, the neuters may be the servant, leader, warrior, or long-distance traveler, but they likely wouldn’t be a protected, cosseted class. Also, neuters would only work in species that had large numbers of children, enough to offset the potential children that are lost due to the neuters’ sterility by increasing the likelihood that the sibling children live.


Humans have some sexual dimorphism, but this dimorphism doesn’t clearly differentiate the two sexes. Although men are larger and heavier than women on average, a particular man may be smaller and lighter than a particular woman. Similarly, there may be subtle differences in shape, fat level, and bone structure, but a particular woman may have a lower fat percentage, stronger muscles, broader shoulders, slimmer hips, or heavier facial structures than a particular male. But imagine a society where dimorphism is much different than in humans.

Size differentiation is very great in some animals. Mandrill males, for example, are typically close to three times the size of mandrill females. Many people assume that this difference is the logical way for species to be dimorphic, with a smaller, weaker child-bearer and a bigger, stronger impregnator that can defend the mother. However the greatest dimorphism often goes in the other direction. Larger females have better nutritional reserves to supply healthy children, so many species naturally select for larger females. Angler fish are an extreme case of this, with the male angler fish being as much as 500,000 times lighter than the female angler fish.(1) They have a parasitic sexuality where the male angler fish permanently attaches to the female, merging their circulatory systems, living off her nutrition, and supplying sperm in return. Societies of species with this sort of extreme dimorphism would likely have much firmer and more consistent gender roles. Gender would probably be tied to specific roles; there might be little flexibility in adopting roles outside one’s gender. On the other hand, species with little or no dimorphism would likely have less consistent gender roles than human societies, even if they have a consistent understanding of gender.

Decoration differences between the genders can be another aspect of dimorphism. Usually, this occurs in species that have one sex choosing or withholding approval of the other, more flamboyantly adorned sex. Peacocks and their much less glamorous counterparts, peahens, are a perfect example of this dynamic. Likely, species with significant dimorphism in decoration would have clearly defined genders and social dynamics with obvious pursuer vs chooser roles.

Mobility differences are less common between genders in a species but can result in strong gender role differences. If one of the genders is sedentary and the other is mobile, then they’d naturally develop societies with major differences in profession and stereotypical personality. For example, perhaps large, rooted females create eggs and mobile males travel around to fertilize them, or perhaps one gender has wings and the other lacks them. Regardless of the type of mobility, one sex being more mobile than the other would substantially affect gender roles, especially regarding property ownership, professional opportunities, and how courtship works.


The third major sex-based difference is childbearing. Among humans, pregnancy requires the female to undergo significant risk and puts a heavy toll on her body. Then, human females need to nurture their babies through infancy, which draws further on their reserves. After weaning, the human children still have a long dependent period where adults care for their needs.

Our big, flexible brains need all that time to develop and then learn to survive, but this extended maturation time comes with significant costs: caretakers must put considerable time and energy into raising and protecting the child, and the mother is vulnerable during pregnancy and recovery. To compensate, evolution has molded us into social animals who are rewarded by taking care of each other, predisposed to particularly care for infants, and motivated to care about our families’ welfare. This leads humans to combine procreation with the formation of social bonds in order to promote the survival and success of their offspring. The constraints of our biology pressure our cultures and societies to develop solutions, such as the institution of marriage.

However, other changes in childbearing and social framework could result in very different arrangements.

Egg-laying species might not have the same physical draining and vulnerability as childbearers do during birth, but whichever gender or genders typically care for the eggs would likely be predisposed to develop skills in defense or protection. The need to develop complex social bonds specifically to nurture gravid mothers would be much lower. Sentient egg-layers would more likely develop large social groups if they were prey species. However, societies with sentient egg-layers at the top of the food chain may be predisposed to form nuclear families or to live solitary lifestyles and less likely to develop a tribal mentality. If this is the case, then in worldbuilding, we have to take special care to consider how culture gets transmitted and how societal institutions form when members are less likely to live in adult groups.

Large litter-bearing species would likely invest less in individual children. Humans greatly prize children, and harm done to children is seen as more egregious than comparable harm done to adults. Having young born in large litters might invert that relationship. They may invest little in children or not consider them family until they pass a developmental threshold. Advanced sentients that have large litters could quickly run into population problems, so worldbuilders using that trope would either need to have them deal with constant population problems, make litters relatively rare, or have a high mortality rate.

Harem species are those where the core social group is a single male, many females, and various children. Unmated males may form their own, separate societies. Lions are the classic example of this. Sentient harem species have some of the same evolutionary pressures that humans do, but one key difference is that they essentially develop two disjunct societies. Many human cultures have distinct male and female spheres; however, the spheres exist within the same political framework. On the other hand, the male and female societies in harem species tend to have overlapping yet distinct boundaries, so their concept of territorial and political boundaries would be necessarily more complex. They might claim territory but also accept others’ claim on the same territory.

Building your own species

Developing a new sentient species is hard. To my knowledge, none of us have first or even third-hand knowledge of an actual alien. The only tools at our disposal are observation of non-aliens, logical reasoning, and imagination. Fortunately, the failure state of doing this hard work looks very much like the original Star Trek TV show, full of alien species that are just variations of humans. That’s not bad as failure states go. Star Trek still did tremendous work in telling interesting stories, building inspiring worlds, and tackling thorny themes about identity and society.

However, thinly disguised humans aren’t the only option available to worldbuilders. If you’re reading this, then you’re ready to challenge yourself to think about what truly alien aliens would be like. You’ll need to identify ways you want your aliens to differ from humans. Then, ask yourself hard questions. With respect to sex and gender, ask yourself whether they have the same sexes as humans. Do they have the same reproductive cycle? Do they fertilize through sexual intercourse or in some other way? How do they bear offspring, and what sort of pressures does this put on the parents? How does this change the development of their concept of gender? How about their gender roles? How does this culture develop social bonds? You’ll need to think about concepts you take for granted and reevaluate whether they make sense for this new species. Would they have the concept of marriage? How about parents? How about love? We usually divide love into romantic, platonic, and maybe familial. Do those categories make sense, or would they divide things differently?

Good luck in continuing the conversation. LeGuin would be proud.

Cathy is a 45 year old mother of three who first started playing tabletop RPGs sometime last century. Her website, The Overprepared GM, contains a variety of topics on Tabletop RPGs.

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Featured Artwork by Adam Bassett


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