Bit of a spoiler, I suppose, but I found out you can make them enjoy a certain activity more the the others by clicking the little boxes next to it. Keeps the researchers researching even after you max out everything, the farmers farming, the builders building, etc. You have to get them a little bit of blue there, but after that even if they wander off, they return quickly.

So I set it for all the men over 40 to be breeders. Every time I started my game you'd hear all this rapid-fire kissing. It was like a machine gun. But the funniest thing was when one of the men near his 60s was about to kiss this sweet young redhead a little less then half his age. He paused before doing it and when I highlighted her, it said she was "praising" while he was standing right in front of her. Then he embraced her and they went into the love shack.