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Yet we aren’t really all that different from our chimpanzee cousins. At a genetic level,
humans and chimpanzees are 96 percent identical (Mikkelsen et al., 2005). At “functionally
important” DNA sites, this proportion reaches 99.4 percent (Wildman et al., 2003)! Yet that
wee 0.6 percent difference matters. It took a human, Shakespeare, to do what a chimpanzee
cannot — weave 17,677 words into literary masterpieces.
Small differences matter among other species, too. Common chimpanzees and bono-
bos resemble each other in many ways. They should — their genomes differ by much less
than 1 percent. But they display markedly differing behaviors. Chimpanzees are aggressive
and their family groups are male dominated; bonobos are peaceable and live in female-
led groups.
The occasional variations found at particular gene sites in human DNA fascinate genet-
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icists and psychologists. Slight person-to-person variations from the common pattern give
clues to our uniqueness — why one person is more susceptible than another to Covid,
why one is tall and another short, why one is anxious and another calm (Ellinghaus et al.,
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2020). Taking advantage of these distinctions, some scientists are now developing gene ther-
apies, which use gene-editing technology to prevent or treat diseases with a genetic basis
(Coller, 2019).
Most of our traits have complex genetic roots. How tall you are, for example, reflects
the size of your face, vertebrae, leg bones, and so forth — each of which may be influenced
by different genes interacting with your specific environment. Traits such as intelligence,
happiness, and aggressiveness are similarly influenced by a whole orchestra of genes
(Holden, 2008). Indeed, one of the big take-home findings of today’s behavior genetics
is that there is no single gene that predicts your smarts, sexual orientation, or personal-
ity. Gene analyses of more than 800,000 people have, for example, identified 269 genes
associated with depression (Howard et al., 2019). Another study of 1.1 million people
identified 1271 gene variations that together predicted about 12 percent of the differences
in people’s years of schooling (Lee et al., 2018). The bottom line: Our differing traits are
polygenetic — they are influenced by “many genes of small effect” (Lee et al., 2018; Matoba
et al., 2019; Plomin, 2018a).

Charles Sykes/AP Photo

Nature or nurture or both? When talent runs in families, as with Wynton
Marsalis, Branford Marsalis, and Delfeayo Marsalis, how do heredity and
environment together do their work?

So, our many genes help explain both our shared human nature and our human diver-
sity. But — here’s another take-home finding — knowing our heredity tells only part of
our story. To form us, environmental influences interact with our genetic predispositions.

10 Unit 1 Biological Bases of Behavior

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