This is technically stuff around the net so I don't feel so bad posting it and shedding some light on the phallacy of nine-toed retarded babies. I recently read the book The Red Queen which is about the evolution of Sex and amongst other things it covers birth defects caused by marriage in families, which was highly practiced in most countries till more recently. First cousin marriages make quite a lot of sense under certain circumstances. Either way, read this about it. http://en.wikipedia.org/wiki/Cousin_marriage#Genetic_aspects