In the past (what feels like a distant past), anime had only one noteworthy quirk in terms of romance subgenres. It was the harem genre; the genre being defined by a group of (almost always) female protagonists vying for the romantic interest of a single male. While this would raise the eyebrows of many non-anime oriented individuals, there isn’t much to say about why such a genre exists. There are many consumer demands and variables that could explain the emergence of such a subgenre: male power fantasy (having a whole crowd of women coming after you sure screams power), adolescence and poor economic conditions (both lead to consumer demands for fantasies to feel power), sexual fantasy and lack of strict moral prohibition on polygamy (then again, even the Christian protagonist George Baily of It’s a Wonderful Life wanted a harem of exotic women).

My point doesn’t rest on if you agree with my causes of the harem genre. My point is the question, “Why does the harem genre exist?” have several potential answers to it, making the question, not a huge problem. But by 2010 there was a romance genre convention that presented questions far more difficult to answer.

I would argue the question “Why is there so much incest in anime?” is far more difficult to answer than why the harem genre exists. For as long as there was sex, there have been men who have wanted to have sex with many women. The same is not true of incest. While there are cultural grey areas between what is and is not “too related” to be considered incest, sibling-sibling unions are almost universally taboo.

Culturally, if the incest taboo is simply a matter of a socially enforced behaviour that emerges purely as a coincidence, then the question I present is easily answered. Just as social norms all around the world are changing, so are those norms in Japan, and it just so happens that the incest taboo has fallen to the sands of time. But there are still questions to be answered. Why in a society that sees the protection of social and cultural practices as a political project would incest be overthrown? Japan has some of the strongest differences in male and female contribution to housework and is far from a shining example of critical theory and social norm reinvention. For this reason, a mere deconstruction of the incest taboo feels an insufficient explanation for the phenomenon. I will turn therefore to a biological approach.

Evolutionary psychologists have argued that an inbuilt attribute of human beings is incest avoidance; the idea being that those human beings who avoid incest spread their genes far better than the ones who partake in incest due to the advantages of heterozygosity (mainly the avoidance of recessive diseases). This adaptive advantage causes those humans (and those genes) that lead to incest avoidance to proliferate. However, many misunderstand the way this phenomenon works. Humans don’t possess a magical radar for those who they are related to. We can’t tell someone is our long-lost brother just by looking at them and realizing we really don’t want to have sex with them. Evidence of a biologically driven incest avoidance mechanism is seen as a developmental phenomenon, where those children who are raised around other children vary early in life do not seem to exhibit sexual attraction to them. This phenomenon was observed in many small communal utopian projects of the 1960s and 70s where children raised in a sex-positive environment with other children never decided to explore sex among their group. The act of being raised together lead to a perception of relatedness that inhibited sexual desire.

What does this have to do with anime? I would argue it is an essential piece of the incest puzzle. Japan has one of the lowest birth rates in the developed world and as a result, most children raised in Japan are only children. Now hypothesize, what prevents an only child from understanding incest is wrong? Social enculturation would advance the culturally agreed incest avoidance measures and the first-hand experience of their parents would lead to parent-child incest avoidance under a potential biological mechanism. But there is no first-hand experience for sibling-sibling incest avoidance. As a result, I argue, a lack of first-hand sibling experience explains how subsections of Japanese society do not feel the typical revulsion to the idea of sibling-sibling incest.

Biology, while potentially being able to explain the lack of incest avoidance, fails to account for incest demand. Incest would not be so prevalent in anime if it were merely passively tolerated. There is a demand that has brought about this ever-increasing incest supply. To answer this, we need to return to culture and power analysis. Depictions of incest that have become ubiquitous have a specific power dynamic to them. The little sister is less sibling and more wife in behaviour. The little sister, in spite of performing domestic labour like cooking meals, cleaning cloths and preheating the bathtub, also is very much a child in terms of submissiveness. In short, the depiction takes the most male-demanded attributes of a wife and combines them with the submissive and childishness of a young woman. The little sister is the vehicle of these traits because there is simple narrative justification as to why she lives with the protagonist, why she does his chores, and why she cares for him, but then extends the familial sense of care into a sexual manifestation.

In this way, the solution to the incest question is similar to the harem question. Both are a male fantasy offering both sexual, emotional and power dynamic related pleasure.

There are limitations to this explanation. The largest being those (mainly western) men who have little sisters but nonetheless exhibit incestuous desires toward little sisters in anime. It is possible that the want for female companionship, sex and power is sufficient to overcome the incest taboo and that there is no need for the biological justification to understand the suspension of disbelief involved. I would argue that the biological argument makes testable predictions that are worthy of inquiry, as it describes the often-observed different degrees of revulsion between those with and without siblings to anime incest. It may be the case that those who desire their actual sisters are detached from their family or have suffered potential traumas to bring about this desire.

In conclusion, the fascination and downright “tropeificaiton” of incest that has occurred within anime can be explained in biological and cultural terms as a function on an increased prevalence in only children, decreasing authority of social norms, and the desire for sexual and emotional satisfaction and power from the predominantly male audience that consumes anime. Future work should be done to see if a biological mechanism of incest avoidance can describe revulsion and desire within the anime community and to what extent the incest culture is a product of those same power fantasies that drive the majority of sexual depictions in anime.