>>9361670>environmental argument>didn't readBe advised, if you already believe that intelligence is due all or mostly to the
environment, new neuroscience facts might be difficult to accept. Denial is a common response when new information conflicts with prior beliefs. The older you are, the more
impervious your beliefs may be. Santiago Ramon Cajal (1852–1934), the father of
neuroscience, once wrote, “Nothing inspires more reverence and awe in me than an old
man who knows how to change his mind” (Cajal, 1924). Students have no excuse.
Historically, most researchers have assumed that intelligence, no matter how it was
defined, develops in childhood and is strongly influenced by environmental factors,
especially home life and social culture. In this view, whatever role genes might play is
minimized, and some even argue for a zero contribution of genes. Although this view about
the importance of early environment seems reasonable, and even flattering to proud
parents, the evidence for strong environmental effects on intelligence, especially in early
childhood, is surprisingly weak, as we will see. Epigenetics provides a concept for the
continued consideration of theories about the importance of environmental factors for
intelligence, but epigenetic research on intelligence is just beginning (Haggarty et al.,
2010). Nonetheless, like climate change, the data that support a major genetic component to
intelligence are compelling and the number of genetic deniers and minimizers is
diminishing rapidly.
Based on cross-sectional data, in young twins 4–6 years old, the heritability of
intelligence estimate is about 40%, and the heritability rises to a high of about 85% when
the twins are older adults. In other words, the genetic influences on intelligence variance
actually increase with age and environmental influences decrease.
