Excerpted and adapted from The 50/50 Solution: The Surprisingly Simple Choice that Makes Moms, Dads, and Kids Happier and Healthier after a Split (Sourcebooks)

Hang out on social media channels devoted to equal parenting activism, you would believe the majority of separated families are lawyered-up, alienating sociopaths at brutal war with benevolent exes, at the mercy of sexist, greedy judges. The answer, they believe, is to pass laws to guarantee a equal parenting presumption.

Meanwhile, there a...