It seems strange that there would be a difference at all. But the researchers, who looked at a large sample of people over a month-long period, found that happiness is associated with selfish “taking” behavior and that having a sense of meaning in life is associated with selfless “giving” behavior.

"Happiness without meaning characterizes a relatively shallow, self-absorbed or even selfish life, in which things go well, needs and desire are easily satisfied, and difficult or taxing entanglements are avoided," the authors of the study wrote. "If anything, pure happiness is linked to not helping others in need.” While being happy is about feeling good, meaning is derived from contributing to others or to society in a bigger way. As Roy Baumeister, one of the researchers, told me, "Partly what we do as human beings is to take care of others and contribute to others. This makes life meaningful but it does not necessarily make us happy.”

The new PNAS study also sheds light on the difference between meaning and happiness, but on the biological level. Barbara Fredrickson, a psychological researcher who specializes in positive emotions at the University of North Carolina-Chapel Hill, and Steve Cole, a genetics and psychiatric researcher at UCLA, examined the self-reported levels of happiness and meaning in 80 research subjects.

Happiness was defined, as in the earlier study, by feeling good. The researchers measured happiness by asking subjects questions like “How often did you feel happy?” “How often did you feel interested in life?” and “How often did you feel satisfied?” The more strongly people endorsed these measures of “hedonic well-being,” or pleasure, the higher they scored on happiness.

Meaning was defined as an orientation to something bigger than the self. They measured meaning by asking questions like “How often did you feel that your life has a sense of direction or meaning to it?”, “How often did you feel that you had something to contribute to society?”, and “How often did you feel that you belonged to a community/social group?” The more people endorsed these measures of “eudaimonic well-being” — or, simply put, virtue — the more meaning they felt in life.

After noting the sense of meaning and happiness that each subject had, Fredrickson and Cole, with their research colleagues, looked at the ways certain genes expressed themselves in each of the participants. Like neuroscientists who use fMRI scanning to determine how regions in the brain respond to different stimuli, Cole and Fredrickson are interested in how the body, at the genetic level, responds to feelings of happiness and meaning.

Cole’s past work has linked various kinds of chronic adversity to a particular gene expression pattern. When people feel lonely, are grieving the loss of a loved one, or are struggling to make ends meet, their bodies go into threat mode. This triggers the activation of a stress-related gene pattern that has two features: an increase in the activity of proinflammatory genes and a decrease in the activity of genes involved in anti-viral responses.