Modern ideas like genetics? You sound as if you don't really approve of such things.
NS much as I enjoy your one brain cell Tommy Robinson routine, it's a bit pointless given there are plenty of doctors over the past few decades in South India who know about genetics, and who would have checked their family history first to assess the risks of any genetic disorders or illnesses before they went into cousin marriages and had children and grandchildren. Lots of them probably married other doctors, who also happened to be their cousins. Which is why most of their cousin marriages produce healthy children. Unless you have any evidence to show otherwise?
Also modern ideas most likely means people not having arranged marriages, not wanting to marry relatives, being open to new ideas and culture by marrying outside their extended family and community rather than continuing traditional culture, finding their own partners, falling in love. Calling these ideas "modern" is a statement of fact. But you carry on with your "the natives are too backward to understand science" approach to the world.