each offering up a part of the story of you. Put the letters together in
the genome and you have the story – provided you have put the
letters together in the right order. Genes also produce the instruc-
tions for how to use materials. For example, they tell your stomach
when to produce stomach acid and how much. If sensation-seeking
is genetic, then the body must produce something physical that
leads to this behavior. It could well be that something in Nick’s DNA
leads to his high sensation-seeking personality. However, DNA
doesn’t make personalities; it makes proteins.
The question is, what does the body produce (or not pro-
duce) in high sensation-seekers? Are they actually programmed
differently than the rest of us? If so, how?
If you are hoping that one day they’ll discover the gene for
sensation-seeking, I wouldn’t hold your breath. Complex personal-
ity factors like sensation-seeking are most likely influenced by what
could be hundreds of genes, each interacting with the environment
in sometimes unpredictable ways. Most research into genetics
doesn’t tell us which specific genes are involved, rather they
attempt to describe the relative influence of all genes and every
environmental factor. And by the environment we don’t just mean
the physical world. The environment encompasses all influences
other than inherited factors, including family, friends, home, work,
even specific experiences from everyday life, such as what we eat,
and things we are exposed to like diseases or toxins.
But what is the best way to determine if Chris and Jess
should sign their baby up for summer rock climbing camp? How
do we determine if Nick’s genes or something in his environment
are responsible for his love of leaping? Too bad he doesn’t have
a twin.
Twins, especially those who grew up separately, are per-
haps the best way to determine the relative influence of biology
and environment.^10 Twin studies are the gold standard of genetics
research and are used to tease apart environmental and biological
influences on traits and behaviors. Since identical twins share
100 percent of their genes, and twins raised together share 100 per-
cent of their environment, examining twins in different families
can be the ideal way to differentiate the relative strength of genes
versus environmental contributions.
From twin studies you can determine what’s called
a heritability estimate. It’s called a heritability estimate because it
describes the influence of heredity and how much of the variation34 / Buzz!Downloaded from https://www.cambridge.org/core. Access paid by the UCSF Library, on 11 Nov 2019 at 14:20:40, subject to the Cambridge