Contraceptives and population growth in the industrialized world
Natural selection doesn't seem to be considered in population projections by the experts on the matter. Why is this? Birth control should be viewed as a massive and sudden environmental change for our species. The resulting new selection pressures are bound to affect our evolution — in various ways — sooner rather than later, i.e., in a few generations rather than in thousands of years. Natural selection will soon catch up with it, and whatever may be now causing certain people to have more children than average (it’s no longer primarily sex drive) will be selected for and prevail in the future (assuming as a premise, naturally, that genetic variation is to some extent responsible for current differences in birth rates), so that eventually the downward trend in population growth will be reversed.