Carpe diem! Did our ancient ancestors have personalities?

I have high school friends who are dead already, as a direct result of their chosen lifestyle. They drank too much, drove too fast, ate whatever they craved at any given moment. They were impulsive, live-for-today types, and they paid a price for these traits. Nobody’s shocked that they died early.

We all know people like this. We also know people who are conscientious workers, homebodies and parents, committed partners and committed bachelors, workaholics, health nuts, easy-going and neurotic. There’s no denying the stark individual differences in personality. “Who we are” seems to emerge early in life, and to endure through the lifespan. It shapes our life choices, from health to family to work and finances.

But why do we have personality at all? It wouldn’t seem to make sense from an evolutionary point of view. The traits that have been wired into our genes and neurons over the millennia tend not to be differences, but things we all share in common--habits of mind that have helped the entire human species survive and adapt. That’s why evolutionary psychologists have tended to dismiss personality traits as irrelevant “noise.”

Until recently. Now a small cadre of psychologists has been revisiting personality, to see how it might fit into an evolutionary understanding of humanity. One of the leaders in this effort is University of Texas psychologist David Buss, who lays out several emerging ideas in the April issue of the journal Perspectives on Psychological Science. Here’s just one:

Each of us has a finite supply of time and energy. Think of a hypothetical young man making his way in the modern world. He might choose to put his energy into prospering—being healthy and well-fed—or he might instead choose the life of a romantic gadabout. Or perhaps he’ll opt for being a devoted parent and provider. But he probably can’t do all these things well. He has to make choices.

So it was with our ancient ancestors. They were similarly called upon to make tradeoffs, spending their time and energy on one life “problem” or another. They probably weren’t as aware of making choices as we are today, but they were nevertheless prioritizing things like romance, parenting, and social climbing.

So the constant challenge that all early humans faced was making the optimal energy tradeoff. The individual choices they made—and continue making today—were shaped by their supply of energy and time, their personal qualities, and their circumstances. Very attractive men, for example, might put a lot of their energy into mating rather than parenting, while people with bleak mating prospects might opt for career or nurturing others’ children.

And those who lack energy, or who perceive the future as short, might discount mating and parenting and career, and squander their limited energy now. Those are the live-for-today types, according to Buss: In that sense, what is often disparaged as a maladjusted personality marked by poor self-control might more generously be viewed as a realistic adaptation to what life throws at you. Carpe diem.

For more insights into the quirks of human nature, visit the new “Full Frontal Psychology” blog at the True/Slant website. Selections from “We’re Only Human” also appear regularly in the magazine Scientific American Mind and at Newsweek.com.