Spoiler Alert: There are no real spoilers here for the Korvali Chronicles trilogy.
When writing science fiction that involves multiple planets and alien species, one has to consider “world building” – i.e. how to create the various worlds in a way that makes them both interesting and believable. In the Korvali Chronicles, we have 5 peoples: humans, Sunai, Korvali, Derovians, and Calyyt. I considered many different factors when creating the worlds, but some of them included how they reproduce, whether they’re dimorphic (i.e. have two genders/sexes), their mating systems (monogamy vs. polygyny), as well as gender roles within each society.
The Korvali, for example, are monogamous by nature. They select a mate, often at a young age, and stay with that person throughout the lifespan. Mothers and fathers have equal investment into their children and form nuclear families. They’re also only mildly dimorphic, where there isn’t a big difference between males and females. This is true for their physical traits: Korvali males and females are similar in height and strength. It’s also true for their roles in Korvali society, where males are females are considered similar and thus equal: whether their malkaris is male or female is merely a matter of who the seat goes to next in the family tree, their government is roughly half female, and patrollers among their primitive clans have females as well as males.
The Sunai, on the other hand, are quite different. They’re polygynous, where one man mates with/marries several women. The women are more invested in childrearing than the men are. They’re also strongly dimorphic, where the men are considerably larger and stronger than the women. Sunai society is strongly male-dominated, with a military government run exclusively by men, and where men make the rules and protect everyone, including women and children. The males are also more aggressive and competitive.
The mating and social systems for the Korvali and Sunai peoples have a basis in the animal world. While these factors vary from species to species, animals with monogamous mating systems tend to have much less sexual dimorphism, more investment in offspring from male parents, and less male aggression (e.g. many species of birds, gibbon apes, a few monkey species). In contrast, animals with polygynous mating systems have much more sexual dimorphism, less investment from males in terms of parenting, and more male aggression (e.g. baboons, gorillas, many mammal species).
These generalizations are common, but they don’t fit every species or apply across the board. Every species is unique, their reproduction and mating systems evolved over time due to whatever pressures they needed to overcome to survive.
Here is some more reading on this topic:
Interestingly, humans don’t fit easily in any category. On the surface, they seem to fall between the Korvali and Sunai in terms of mating systems, sexual dimorphism, and male dominance. In reality, however, there is evidence for a variety of mating systems among humans.