Hmm.

There's an psychological effect that people who grow up alongside someone generally aren't attracted to them to the extent that they might be to someone else.

Can't remember the name of the phenomenon.

kagis

The Westermarck effect.

https://en.wikipedia.org/wiki/Westermarck_effect

The Westermarck effect, also known as reverse sexual imprinting, is a psychological hypothesis that states that people tend not to be attracted to peers with whom they lived like siblings before the age of six. This hypothesis was first proposed by Finnish anthropologist Edvard Westermarck in his book The History of Human Marriage (1891) as one explanation for the incest taboo.[1]

The Westermarck effect has gained some empirical support.[2] Proponents point to evidence from the Israeli kibbutz system, from the Chinese Shim-pua marriage customs, and from closely related families.

In the case of the Israeli kibbutzim (collective farms), children were reared somewhat communally in peer groups, based on age, not biological relations. A study of the marriage patterns of these children later in life revealed that out of the nearly 3,000 marriages that occurred across the kibbutz system, only 14 were between children from the same peer group. Of those 14, none had been reared together during the first six years of life. This result suggests that the Westermarck effect operates from birth to at least the age of six.[3]

In Shim-pua marriages, a girl would be adopted into a family as the future wife of a son, often an infant at that time. These marriages often failed, as would be expected according to the Westermarck hypothesis.[4]

Studies show that cousin-marriage in Lebanon has a lower success rate if the cousins were raised in sibling-like conditions, first-cousin unions being more successful in Pakistan if there was a substantial age difference, as well as reduced marital appeal for cousins who grew up sleeping in the same room in Morocco. Evidence also indicates that siblings separated for extended periods of time since childhood were more likely to report having engaged in sexual activity with one another.[5]

You'd expect the Westermark effect to decrease attraction for someone that a person grew up alongside, but not to decrease appeal of other people who are siblings having sex.

I'm not aware of any formal study as to the effect, but I'd assume that some of the appeal of what people consider kinks derives directly from the fact that something is, in fact, taboo. Like, let's say that we had no incest taboo in present-day society -- and that hasn't been a universal -- then I'm not sure that "incest porn" or the like would be a thing.

kagis

https://worldpopulationreview.com/country-rankings/countries-where-incest-is-legal

Twenty-two countries around the world have not criminalized incest. Portuguese law, for example, does not criminalize incest. Additionally, no laws prohibit consenting relatives from having sexual relations in France, Belgium, and Luxembourg. Incest is also legal in Argentina, Brazil, India, the Ivory Coast, Japan, Latvia, South Korea, Thailand, and Turkey.

In Spain, Netherlands, and Russia, consensual incest is fully legal. However, siblings may not marry, nor may half-siblings or a step-parent and a stepchild. In Serbia, Lithuania, and Slovenia, incest between an adult and a minor is illegal, but the law does not prohibit minors or adults from engaging in incest with partners in the same age category. Israel outlaws incest among minors but declares it legal if both persons are over 21 years old. Perhaps the most unique laws on incest come from Ireland and Germany, where the language forbidding incest specifically addresses male-female pairings—which means incest remains legal for same-sex couples.

Of course, legal prohibitions aren't exactly the same thing as having a cultural incest taboo.

https://en.wikipedia.org/wiki/Incest_taboo

I'd guess that to test that, one could probably run a study, come up with some kind of quantitative measure of how intensely "taboo" incest is in a given society, and try to see whether there is correlation with frequency of incest pornography.

EDIT: Hmm. You know, that makes me think that if a correlation between cultural taboo and popularity of a kink exists, maybe you could use the effect in reverse as a metric for hard-to-measure cultural taboos.

Like, okay. In 2024, there are no legal prohibitions on miscegenation. Like, if someone of Race A and someone of Race B want to have a kid, the law isn't going to stop them. But there's definitely some level of cultural taboo floating around out there. I'm pretty sure that it's going to be hard to get someone to fess up to their views on that.

But...you can get aggregate data on frequency at which people are consuming interracial pornography. If you figure that the kink derives from the cultural taboo, then a sociologist has got themelves a pretty interesting metric right there on racial views.