THE ROUGH GUIDE TO PSYCHOLOGYtheir influence is far more modest. So whereas research had shown
that, say, conscientious parents tend to raise conscientious children, the
new field of behavioural genetics demonstrated that this was probably
because of genetic factors, not parenting style. For a post-war culture
obsessed with the importance of parenting, these claims were explosive.
It’s important to add a caveat here. The findings showing the modest
role played by the family environment pertain to unexceptional circum-
stances. There’s no question that neglect or abuse can have a devastating
effect on a child’s development.
It’s also important to recognize that genetic and environmental effects
are not separate. A person’s genetically influenced traits and endow-
ments affect the kind of environments they place themselves in. A more
intelligent child is more likely to end up at a superior school; a lanky
teenager more likely to wind up on the basketball court and thereby
receive more coaching. Similarly, many genes are like switches, turned
on by particular environments. In fact there’s a whole field, known as
epigenetics, which seeks to discover the processes that control whether
or not a particular gene is expressed. This means that for many traits
and illnesses, it is impossible to say whether the cause is either genetic
or environmental. A good example of this is phenylketonuria, a genetic
condition which prevents the digestion of phenylalanine, an amino acid
found in fish, meat and other foods. With the right diet, phenylketonuria
causes almost no problems. However, if a person with phenylketonuria
eats foods containing phenylalanine they develop severe cognitive
deficits. Are these problems caused by genes or the environment? The
answer, as with so many other outcomes, is surely both.
BIRTH ORDER
One of the most popular folk-psychology explanations for why we differ is
birth order – first-borns are traditionally considered to be high-achieving
go-getters, while younger siblings are often seen as more rebellious and
creative. There’s certainly plenty of anecdotal evidence to back this up.
First-borns are hugely over-represented among past leaders from all
over the world, including British and Australian Prime Ministers and
American Presidents. Similarly, a recent survey of international corpora-
tions reported by Time magazine found that 43 percent of chief executive
officers were first-borns whereas just 23 percent were last-borns.
In some ways, the apparent success of firstborns makes sense. After all,
they have all the attention and resources of their parents to themselves,