Virtually every other mammal engages in sex with siblings/parents, etc.
So you're going to have to demonstrate how regulation-of-incest has "improved" our survival chances.
Many people mistakenly believe that modern medicine improved our survival chances... and yet, this lead to our over-population crisis which might contribute to the extinction of humanity and many other species.
So how does incest regulation help humanity survive better?
Don't genetic mutations (like the ones created by incest) actually give humanity more "types" to throw at the environment? More mutations are better for survival, aren't they? doesn't incest create a kind of mutation?