I think you'll find it's a bit less complicated than that
There are only three forms of family structure, got it. Then what are the causes of cohabitation and single motherhood? Culture (e.g. Haidt/Schwartz, Economy, Authoritarianism), Genetics (e.g. Life History, IQ, Personality), both?
Genetics cause all forms of behaviour to some degree (http://faculty.umb.edu/peter_taylor/epi/turkheimer00.pdf). But what matters is the change over the past 50 years, and that is very unlikely to be genetics.
There are only three forms of family structure, got it. Then what are the causes of cohabitation and single motherhood? Culture (e.g. Haidt/Schwartz, Economy, Authoritarianism), Genetics (e.g. Life History, IQ, Personality), both?
Genetics cause all forms of behaviour to some degree (http://faculty.umb.edu/peter_taylor/epi/turkheimer00.pdf). But what matters is the change over the past 50 years, and that is very unlikely to be genetics.