Of especially great concern is what will happen on a long-term mission, like the ones now in the planning stages for a manned flight to Mars, or even an extended stay on something as relatively close by as the Moon. Space experts agree that humans are, by nature, beings who require sexual activity and expression in order to remain both emotionally and physically healthy. In more than forty years of forays into space, we've learned how to deal with just about every other human physiological need... and now we're going to have to confront the final frontier if we are to consider going any further.
It all sounds funny. But it's not.
Think about it: if we are bent on being an extra-planetary species, then what's going to happen to children who are conceived, and then grow up, in either a micro-gravity environment, or on a world with two-thirds or less of Earth's gravity? The movie WALL-E had some fun with that idea. But in reality, someone who matured in such an environment might very well die if he or she came to Earth, from failure of the body to acclimate to the higher gravity.
(And on a geeky note, the failed ABC pilot movie Plymouth back in 1991 took a very serious and engaging approach to this notion. It was yet another idea for a television series that was way ahead of its time...)
Of course, it would be remiss if one did not note that at least this would bring a whole new meaning to the term "panspermia"...
Okay, I'm stopping now.