Based on the notion that the hormone oxytocin plays an important role in the ability of nonhuman mammals to recognize each other and form attachments, the researchers gave 60 men a shot of oxytocin or a placebo, and then showed the subjects photographs of a bunch of people. Some faces were obviously angry, some happy, and others neutral. The next day, the men who were swimming in oxytocin remembered the happy faces but couldn’t recall the angry or neutral ones.  

While it’s interesting that a shot of oxytocin can put men into la-la-land when it comes to interpersonal relationships, the more interesting point is that women are more often already awash in the stuff.

PS: My wife and I have six children (and hopefully more to come) and while our lives are stressful, we are very happy and hopeful. I’d say that we are generally happier than most people. This just shows that having large families is not contrary to happiness.