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Comment by da_chicken | Hacker News Reader

No, we've understood heredity for a very long time, and sex between siblings or between parents and children has always been a taboo. Cousin marriage, however, is not particularly harmful (https://www.psychologytoday.com/blog/animals-and-us/201210/t...).

The real reason we stopped marrying cousins is:

1. We started to live in large cities instead of on farms and ranches. (https://www.census.gov/population/censusdata/table-4.pdf)

2. We could reasonably travel more than 10 miles from home in a day.

In other words, we used to marry cousins because it was too difficult to find better prospects.

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"The real reason we stopped marrying cousins is:..."

Perhaps in the majority groups in the West. Certain communities in the UK still widely practice cousin marriage and suffer hugely in genetic abnormalities. They are not constrained by transport, it is a cultural thing that has not yet been updated.

Two of my great-grandparents were first cousins. We blame every bit of nuttiness in our family on this, whether or not it's fair :-D

Though close relatives marrying is bad for the children's health, it's actually a slight benefit for the grandchildren, great-grandchildren, etc.

Why that's true: The reason inbreeding is bad is that the child is at risk of inheriting two copies of a nasty recessive mutation, in a region of their genome where both versions came from the same recent ancestor. However, if the child goes on to successfully reproduce, it's more likely that they had zero copies than two--and in that case the grandchildren have zero copies, which is good for them.

http://www.bbc.com/news/uk-england-leeds-23183102

http://www.dailymail.co.uk/news/article-1392217/Muslim-outra...

It's noteworthy that it's simultaneously socially unacceptable to criticize Pakistanis for their preference for first cousin marriages, despite the undeniable harm caused by it, and yet it's also socially unacceptable for whites to have the much less incestuous preference for just marrying other whites, despite the absence of harm:

http://www.slate.com/articles/news_and_politics/politics/201...

The first article you link to is a BBC news article that says exactly what you claim it is socially unacceptable to say. In the second article, the only people getting outraged are those who've been referred to as "inbred". You can hardly expect them to take kindly to that description.

https://www.express.co.uk/news/uk/591577/British-Pakistanis-...

> Baroness Flather said because of 'inbreeding', members of the ethnic group are 13 TIMES more likely than the rest of the UK population to have disabled children.

> The Pakistan-born peer has called on the Government to take steps against the issue of unions between close relatives in Muslim communities, which she called an "outdated, un-British custom".

...

> She also accused Britain of a "cowardly reluctance to tackle damaging social practices within certain ethnic minorities".

> In what has been described as a brave attempt to break a taboo she said there was a fear of "accusations of racial prejudice" which has made the issue "unsayable".

> She added: "That is certainly what happened over the disgraceful sex-grooming scandal in Rotherham, in which the civic authorities, including the police and social services, tried to cover up the systematic abuse of more than 1,400 vulnerable girls by predatory gangs of Pakistani heritage men."

extensive scientific evidence contracts your claim that it is "not particularly harmful":

http://www.bbc.co.uk/bbcthree/article/6af25e7b-0545-42ba-a6f...

http://www.bbc.com/news/uk-england-leeds-23183102

http://www.independent.co.uk/life-style/health-and-families/...

http://blogs.jpmsonline.com/2015/12/07/cousin-marriages-a-pu...

https://www.ua-magazine.com/first-cousin-marriage-doubles-ri...

The issue there is probably with the practice being common and repeated through many generations. The risk of generic abnormalities is not particularly high for cousin marriage.

yes, a single instance is not extremely risky from a statistical perspective, it's when the children of first-cousin marriages repeat the practice for several dozen generations... some really bad things can crop up.

Even that's not enough, you need a small population, small number of children each generation, and for harmful mutations not to be weeded out. A wild Frog species that has 100 eggs could have regular 'first-cousin' marriages without significant issues beyond infectious diseases.

Humans unfortunately tend to accumulate negative mutations more easily. Though the upside of lack of predation etc is not something I would want to pass up personally.

I haven’t yet read the scientific article that it’s based on, but the OP points out that there’s about a 50 year lag between the move to cities and a decrease in cousin marriage, so there was probably some cultural component.

Oh, certainly. Any culture takes time to develop a taboo like that. It's especially hard to damn the behavior of your own parents when their union led to your own existence. Only when everybody who was married has died will there really be a change.

"2. We could reasonably travel more than 10 miles from home in a day."

No, this is not the reason. Plenty of societies had very strong norms against cousin marriage centuries ago -- from memory below 1 percent in colonial new england?

Others did not. Sometimes because they were just far from the enforcers of such norms. But often for deliberate reasons of keeping family and property together. Saddam Hussein wasn't short of private jets, but was very concerned about losing power, and blood relatives are more reliable. And about 50 percent of his countrymen feel the same way.

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