46 CHAPTER 2
P SN FEEDBACK LOOPS IN ACTION: The Genes and
the Environment
We’ve seen how genes can affect the environment, but—to the surprise of many—
the genes themselves are also affected by the environment, including psychological
and social factors. We consider the feedback loop between the environment and the
genes in the following two sections.The Environment Affects the Genes
Many people seem to think of genes as instructions for building the brain and the body,
guiding the construction process and then ceasing to function. For most genes, this is not
so. Even in adulthood, a person’s genes are being regulated by the environment (Hyman
& Nestler, 1993). Consider a simple example: Did you ever try to learn to play piano?
If you did, your fi ngers were probably sore after even a half-hour of practice. But if you
stuck with it, you could play for longer and longer periods with no discomfort. What
happened? Your muscles got stronger—but how? When you fi rst began, the stress of us-
ing your fi ngers in new ways actually damaged the muscles (which is why they felt sore).
Then, a series of chemical events inside the muscle cells of your fi ngers turned on genes in
the nuclei of these cells. These genes directed the cells to produce more proteins, to build
up the muscles, which made them stronger. If you stopped playing for a period of time,
those genes would turn off, and the muscles would become weaker. Which is why your
fi ngers might be sore when you fi rst resumed playing after having taken a long break.
The point is that some genes are activated, or turned on, as a result of experi-
ence, of interacting with the world (Kandel, Schwartz, & Jessell, 2007). This is true
of genes in the brain that produce neurotransmitters and that cause new synapses
to form. In fact, when you learn, genes in your brain are turned on, which causes
new connections among neurons to be formed. This is true even when you learn
maladaptive behaviors, which can produce, among other problems, a phobia—an
intense, irrational fear of an object or situation.
Moreover, genetic factors can contribute to a neurological vulnerability for a
psychological disorder. For example, genetic factors can lead a person to be prone
to learning maladaptive behaviors.
However, genes are not destiny. More often than not, having specifi c genes does
not determine behavior, but rather predisposes one to be affected by the environment
in certain ways. That is, genes can predispose a person for a specifi c disorder, but those
genes may have that effect only when triggered by psychological or social factors.The Genes Affect the Environment
We’ve just seen how the environment affects the genes, and we’ve already noted that
the reverse also occurs. Let’s now look in more detail at ways in which the genes
affect the environment. Many researchers (Plomin et al., 1997; Scarr & McCartney,
1983) distinguish three ways in which genes affect the environment—passive inter-
action, evocative interaction, and active interaction:1.Passive interaction. The parents’ genes affect the child’s environment—and the
child passively receives these infl uences. For instance, some parents avoid large
social groups because they are shy, which is in part a result of their genes; this
means that their child does not have many social experiences. The child may not
have inherited the parents’ shy temperament, but the parents’ genes nonetheless
act through the environment to affect the child.2.Evocative interaction (also called reactive interaction). A person’s inherited traits
encourage other people to behave in particular ways, and hence the person’s social
environment will be affected by his or her genes. For example, if you are very tall
and heavy-set, others may respond to you somewhat cautiously—in a way they
would not if you were short and frail. Similarly, others may approach or avoid you
(fairly or not!) in response to your temperament (e.g., shy, calm, high-strung); any
specifi c temperament will appeal to some and not to others. Thus, even your circle