Evolution leads to strange relationships. If survival of babies conceived by abortion families is lower than those on the big family squalor side of the debate, then the genes of the latter will design the pool of heredity.

In primitive societies where bonding with a mighty male made all the difference to the actual life or death survival of her children, a woman's choice to stick with her mate, at least until the child is old enough to survive on its own, is encouraged by the genes of her ancestress who did that.

In modern reality, where the survival rate of all babies is high regardless of whether a male hunter/warrior is present in the home, the two-parent family is no longer the winning niche that it was.