THE THREE BROTHERS—CALLED HM, HT1, AND HT2 in the scientific literature, to maintain their anonymity—were close. They grew up together; attended the same grade school, high school, and college; and hung out together as adults. Did spending all this time together, in the same neighborhoods and schools, cause them to develop similar personalities?

HT1 and HT2 did resemble one another psychologically. In childhood, HT1 was seen as stubborn and strong-willed, and HT2 was athletic and cocky. It was easy to see the resemblance. HM, however, differed from them. The parents described HM as delicate, sensitive, and artistic. An old home video supports their description: HT2 is seen boxing with an older relative, then HT1 starts boxing with HM. But HM so detests fighting that, rather than starting to box, he starts to cry.

Once they reached their teen years, HT1 and HT2 became interested in girls. When they grew older, their sexual partners were women. Again, HM differed. One day during his childhood, in a restroom at a baseball stadium, he noticed how much he enjoyed looking at men’s genitals. In high school, he became sexually attracted to a male teacher. By his late teen years, HM knew he was gay.

The brothers’ similarities and differences raise questions we address in this chapter on nature, nurture, and their interaction. Are psychological characteristics such as personality style and sexual orientation inherited—part of your genetically determined biological nature? Or are they learned—a result of the family, community, and culture in which you are nurtured?

What’s your guess? Why, for example, do you think the brothers HT1 and HT2 were similar? Perhaps the cause was nature, that is, similar genes. If that’s what you are thinking, it’s a good guess; HT1 and HT2 are identical twins, and thus have the same genes. Their genetic similarity might explain their similar personalities and sexual orientation.

Why do you think HM differed? It doesn’t seem as if the cause was nurture, because HM and his brothers grew up in the same environment. So maybe, again, it is nature: Perhaps genetic differences between HM and his identical-twin brothers produced their psychological differences. But if that’s your guess, you’re in for a surprise: HM had the exact same genes as HT1 and HT2—the three brothers are genetically identical triplets (Hershberger & Segal, 2004)! HM’s personality and sexual orientation differed from that of his brothers, even though he had the very same genes as them and was raised in the very same household.

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Are psychological qualities thus a product of nature? Or nurture? Or what? The chapter ahead will provide some clues.

IMAGINE THAT YOU HAD different genes, the molecular material in the cells of your body that is the basis of biological inheritance. Instead of the genes you inherited from your parents, suppose you had genes from some other parents, yet were raised in the same household where you actually grew up. Do you think that, psychologically, you would be the same you —with the same thoughts and feelings, abilities and potentials, hopes and fantasies?

Now imagine that instead of having different genes, you were raised in an entirely different environment: a hunter-gatherer society with no stores, schools, or mass communication; or a Buddhist monastery, isolated from the outside world, where you meditated for hours a day. Do you think you would be the same you —with the same thoughts, feelings, abilities, potentials, hopes, and fantasies?

Likely your answers are “no” and “no.” Even before reading this chapter, you know intuitively that your psychological makeup is influenced by your biological nature —qualities you inherited genetically. You also know that your psychology is shaped by nurture —the ongoing stream of experiences you have had since your birth.

“So,” you may be asking yourself, “if I already know that nature and nurture are important, what am I going to learn from this textbook chapter on nature and nurture?” In a nutshell, you’re going to learn how to think like a psychologist about nature and nurture. Two tales about nature and nurture will show you exactly what that means.