If I choose to always be happy, I would miss out on the information provided by being unhappy, the information that life is going poorly and that something needs to be done. Unhappiness—like a gas gauge telling you that you are approaching empty, like an aching empty stomach—is a gift.

This question forces us to confront what happiness is for. A plausible enough evolutionary account is given by Steven Pinker:58 We can see happiness as the output of an ancient biological feedback system that tracks our progress in pursuing auspicious signs of fitness in a natural environment. We are happier, in general, when we are healthy,

But why? Here we are presented with our usual trio of options when thinking about the relationship between two factors. A can cause B; B can cause A; or a third factor, C, can cause both A and B, but A and B might not be otherwise related. It might be that marriage makes you happy (plausible enough), or that being happy makes you more likely to

In the 1800s in the United States, enslaved people who escaped were proposed to be suffering from drapetomania—an insane compulsion to wander. More recently, the diagnosis of homosexuality as a mental illness was broadly accepted by many psychologists and psychiatrists. It was only by the DSM-III, published in 1980, that this was changed after a

Together, this is it; everything is either heredity, shared environment, or nonshared environment. Psychologists—and everyone else—are fascinated by the extent to which different forces make us what we are. Some people are more anxious than average, say. To what extent is this because of their genes, to what extent is it due to shared environment

These points were anticipated by the philosopher Adam Smith long ago. In his book The Theory of Moral Sentiments, published in 1759, Smith discusses the qualities that are most useful to a person and comes up with the following (note that “superior reasoning and understanding” is what we are calling intelligence, and “self-command” is what we now

This might all seem obvious—of course people have different personalities! But there’s long been a debate in psychology over how much personality matters when it comes to explaining what people do.3 To take an extreme example, if you wake up surrounded by smoke and fire, you’re likely to be anxious, but it would be a mistake to say that this is due

One classic study that purported to demonstrate this was led by the psychologist Muzafer Sherif. In the 1950s, Sherif got twenty-two ten- and eleven-year-old boys, all with a Protestant, two-parent background, all white and middle class, to enlist in a fake summer camp at Robbers Cave State Park in Oklahoma.16 Yes, fake. Social psychology

percent and 2 percent, respectively.11 Then there are the moral issues that arise. Racial profiling by police is an obvious example. Defenders of the practice claim that this is more efficient, but even if it were, it makes life worse for the people who are profiled, the vast majority of whom are innocent of any crime. I’m framing the issue here in