In the making of a human, how much is nature, how much is nurture?
That is to say, what is the relative influence of genetic inheritance
versus the effect of parenting and experience? These are questions
with political as well as scientific import. It’s an unpalatable fact to
some, but we’re certainly not born equal. Some people are predis-
posed to be more intelligent than others, some faster, bigger, nastier,
lustier. However, there is no optimum human form – different people
are better suited to different situations. We’re each equipped with the
characteristics and inclinations that allowed our ancestors to thrive in
the social and physical worlds in which they lived.
Why we differ
Broadly speaking, there are three main influences that make each of
us unique. There is our genetic inheritance; there’s the family environ-
ment, which we share with any siblings we may have; and, finally, there
are unique environmental effects, which are those experiences that we
alone encounter. Untangling these three influences is no mean feat, but
great progress has been made in recent decades, particularly through
the use of twin- and adoption-studies in an emerging field known as
behavioural genetics.
Monozygotic (identical) twins develop from the same ovum and sperm
and therefore share all their genes. Whether raised together or not, such
twins tend to be far more similar in numerous traits, including person-
ality and intelligence, than raised-together dizygotic, non-identical
twins who are formed from separate eggs and sperm (and so share only
half their genes). This provides compelling evidence that genes play an
important role in shaping our psychological make-up.