Yikes, I just realized I spoke too soon!
Even the enjoyment people derive from exercise seems to have a strong genetic component. In my previous post, I made the same logical fallacy I suggested many others do: projecting ones personal experience to the greater human condition. The truth is that swimming makes me feel quite good--it dejangles my nerves, relaxes me, clears my mind, and usually leaves me feeling happier than before the workout started. In this I realize that I am the beneficiary of genetic influences that perhaps allow me to sop up excess adrenaline, or release endorphins, or benefit from some other biochemical byproduct of exercise that not everyone derives. We've all known people who get nothing pleasant from exercise, or whose state of contentment is such that they do not require it for psychological balming purposes.
I guess people who are naturally lean should accept with humility their good fortune in the genetic lottery (though this could change if the world economy collapses and the threat of famine once again raises its head in our land!) Likewise we who like exercise should not assume everyone gets the same enjoyment from it, and judge them harshly for avoiding it, but rather just consider ourselves fortunate that our physiology, for whatever reason, provides us a motivating reward that makes it easy to keep coming back to the pool, year after year after year.