Let me make it plain

Betsey Stevenson and Justin Wolfers at Cato Unbound note that the economic basis of marriage is changing. No longer is it economical to have one person stay home and do housework while another goes out and works. Instead, people now get married simply to share their lives with someone else. They write:

[M]odern marriage is about love and companionship. Most things in life are simply better shared with another person: this ranges from the simple pleasures such as enjoying a movie or a hobby together, to shared social ties such as attending the same church, and finally, to the joint project of bringing up children...We call this new model of sharing our lives “hedonic marriage”.

The Economist's economics blogger frets that "hedonic marriage" will kill fertility rates:

This "hedonic marriage" business sounds decadent. Can we count on overgrown teenagers seeking only self-actualisation and bound only by puppy love to take seriously their duty to fill the nation's wombs with enough future taxpayers to meet pension liabilities? Probably not!

Leaving aside for a moment the distasteful tone of this remark - does marrying for companionship really qualify people as "overgrown teenagers"? - it strikes me that whoever wrote this didn't think very carefully about the determinant of fertility rates. In Japan, where many women still stay home, ferility has dropped to an unsustainable 1.3, while in America, where most women work, it's still at the replacement rate. So much for that argument.

In the longer term, though, what will hedonic marriage mean for fertility? With the advent of family planning (thanks to The Pill), most people who now have kids are people who want kids. And married couples are more likely both to want kids and to be able to rear them effectively. This means that, for the first time in world history, people who want kids may be more fertile than people who only want sex - and the fertility rate will rise again.

Which means, in the not-so-distant future, our species will evolve more and more toward a species that likes kids - in other words, "hedonic child-rearing." That bold new humanity is on its way.