> still is across what's now the muslim world (although I think it long predates Islam).
It can trivially be seen to have little to do with islam in examples like the House of Habsburg, and the famously ignominous end of the Spanish line. Or orthodox jews (the endogamous set is wider than just a family, but you still see lots of rare genetic conditions crop up, and some jewish communities don't even stray outside of it e.g. Mashhadi jews).
Though it does look related to Arabization.
While first-degree cousin marriage has gotten quite a bit rarer used to be extremely common across the globe, and aside from the middle-east it also remains legal throughout eurasia (except for a few eastern european countries and notably china where it's entirely banned and india where it's dependent on culture and religion) and south america
> IIRC it's much less common in Hindu tradition
It's less common but hardly non-existent: according to Shrikant Kuntla, Srinivas Goli, T.V. Sekher, Riddhi Doshi via wikipedia[0] rate of consanguinous marriage is 25% of indian muslims, 15% for indian hindu, and under 10% for other indians. State / culture presents a much wider spread, from 1.2% in Himachal Pradesh to 38% in Tamil Nadu.
[0] https://en.wikipedia.org/wiki/Cousin_marriage#India