Why are Cousin Marriages so common in South India?

On October 12, 2023, Medium had an article about cousin marriage:

Cousin marriages, particularly between first cousins, are relatively common in some regions of South India, and there are several historical, cultural, and social factors that contribute to this practice:

Cousin marriages have been a part of South Indian culture and tradition for centuries. They are often seen as a way to maintain family and community ties and strengthen family relationships.

South Indian society has a strong emphasis on the caste system, which traditionally influences marriage choices.

Marrying within the same caste or sub-caste, including cousin marriages, has been a way to preserve social and economic structures.

Cousins often live in close geographical proximity to each other, which makes it easier for families to arrange marriages. It can also contribute to the familiarity and comfort between cousins.

Marriages in South India are not just the union of individuals but also the union of families. Marrying a cousin is often considered a way to strengthen family bonds and maintain social harmony.

Marrying within the family can help keep family property and assets within the same family group.

More than just kissing: cousins and the changing status of family

Jenny DiPlacidi is the author of the 2018 book "Gothic incest: Gender, sexuality and transgression". Chapter 4 is called "More than just kissing: cousins and the changing status of family". JSTOR has a digital copy of the book. Here is an excerpt:

Amongst the many tangled familial relationships in the Gothic that are fraught with incestuous desires and passions, cousin relationships occupy a curious space in which the incestuous nature of the bond is at once diminished and heightened by its relative acceptance by both English society and the law. Cousin marriages may be more permissible than other relationships between blood kin because the consanguineal tie, in terms of shared genetic material, is weaker than those between the more taboo incestuous relationships, such as mother-son, father-daughter or brother-sister. The difficulty in coming to a clear consensus regarding the incestuous nature of cousin marriage is demonstrated by the irreconcilable differences between leading scientists and anthropologists on cousin incest. Sociobiologist Joseph Shepher argues that 'most cultural forms of mating', including preferential cousin marriages, 'represent cultural regulations aimed at optimum inbreeding'. Shepher defines incest as 'mating between relatives, called inbreeding' and that 'as a technical term, inbreeding is reserved for cases in which discernible traces can be followed back to common ancestors within two to three generations'. Certainly cousins count in this regard, their shared relations being grandparents.

Drunk teenager slept with cousin at family wedding before discovering who she was

On May 3rd, The Mirror had an article about romance at a family wedding:

“A girl I don’t recognise begins to dance with me on the very crowded dance floor. She’s older than me clearly, but I thought maybe 19 or 20. Anyway, we start dancing, touching, etc. She twerks on me a little, I grind a bit and I presume nobody noticed due to accumulated intoxication and crowdedness around where we were.

“One thing leads to another, we start kissing and she asks me if I want to go ‘upstairs’, which I correctly take to mean her room in the hotel (it was a hotel wedding). I, of course, being a hormonal teenage boy, jump at the opportunity and say yes. I should say this wasn’t my first time or anything and by this point, I carried condoms around in my wallet when I went out and knew I would be drinking.

“So we proceed to discreetly (or so I think) take our leave. Both are drunk, obviously, but not to the point of not being in control of our actions, or stumbling around/blackout etc. I get to her room, a bit of excited talk, and clothes come off. All is going well. Now, I should say that all this time I’m assuming this girl is a relative or perhaps a friend of the bride, but oh boy. I was in for a shock. Because, as it turns out, she thought the same of me.

“As we were ‘cleaning up’, so to speak, we began a little small talk when before had mostly just been purely sexual. She eventually asks how I know the bride. I stop. Thunderstruck. The realisation slowly creeping up on me and oh, the horror. I laugh it off, hoping, in vain, she is joking and state I am the son of (insert mother's name).

“The shock is palpable on, what I then realised, was my cousin's face as she was putting her bra back on. She sort of freaks out and says she’s the estranged daughter of one of my uncles who’s had a troubled life, whom she had very recently reconnected with.

What’s the genetic disease risk for children of related couples?

In 2012 The Conversation had an article about cousin marriage:

Marriages between people who are related is more common than you might think. Unlike what many people think, their offspring are not doomed to birth defects or medical problems.

In fact, unless they both carry the same gene mutation, the couple’s chance of having a healthy child is almost as high as any other couple. Let’s examine why, through the story of one couple.

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Without a family history of an autosomal recessive condition, Maria and Max have an 8% chance of having a child diagnosed with a problem after birth. In other words, their chance of having a healthy baby is greater than 90%, a figure that most people find quite reassuring.

This figure is not too different to the general population risk of having a baby with a birth defect. Most related couples accept this risk and focus instead on general measures to have a healthy baby, such as taking folate, losing weight, and reducing their intake of alcohol and cigarettes.