Isn't having twins an evolutionary advantage?

I don't think it is an advantage. Having twins is more difficult for the mother. They weigh more, are harder on her body, and require her to eat more. There are complications with having twins that don't happen with singletons. read more

Having human twins is an evolutionary disadvantage. Female humans are equipped to carry one child even though they have two breasts. Males have two breasts too but can’t carry even one. Having twins increases the danger to the mother and the children. read more

Having two children who leave no offspring would not give you an advantage over having one child who leaves many offspring. Or any combination thereof. Twinning is a developmental thing of egg doubling or fraternal twins being just like siblings. read more