Those who ride to work in overalls and on the bus are just as happy on average as those in suits and ties who drive in their Mercedes. Second, to explain these curious results, the Illinois researchers have shown that the effects on current SWB of both positive and negative life events are largely gone after just 3 months and undetectable after 6 months. One further replicated finding is that most people's happiness set-point is above zero, that is, on the happy side of neutral. It seems plausible to suppose that, over the millennia of human evolution, those ancients who were grouchy or sad did less well in the struggle for survival and had less luck in the mating game. Our species has become biased toward positive well-being by natural selection.
Many interesting questions remain to be answered.
That emotional lability, too, is genetically influenced could be tested by repeatedly assessing our middle-aged twins, say, weekly for a year. Cyclothymic individuals, and certainly the more extreme cyclothymes with bipolar affective disorder, seem to have variable set-points. Meanwhile, however, there are important implications of the findings already in hand. Much of the angst and debate generated by Herrnstein's and Murray's The Bell Curve stemmed from the apparent unfairness of their demonstration that successful people have higher IQs on average than do less successful people and that individual differences in IQ are determined largely by genetic differences. The scientific support for these conclusions is unequivocal and strong.