The book begins with a description of what has generally become known as "the Flynn effect":
the steady rise from one generation to the next in average scores on IQ tests over time. Flynn
notes that this effect apparently contradicts some fundamental beliefs about IQ long held
by human intelligence researchers, and categorizes these contradictions into four seeming
"paradoxes":
1. The factor analysis paradox – past research has shown evidence for a single
factor, "g" or general intelligence, underlying IQ. However, the Flynn effect
happens to different degrees in the sub-tests of the WISC test, suggesting that
intelligence as measured by IQ tests is multidimensional. Flynn poses this as:
"how can intelligence be both one and many at the same time".
2. The intelligence paradox – the Flynn effect shows significant improvements in
IQ over a short time scale, yet we do not notice in everyday life that young
people are significantly smarter than their parents or grandparents.
3. The mental retardation paradox – the IQ level commonly associated
with mental retardation is 75. If the Flynn effect is extrapolated back to 1900 the
mean IQ would be somewhere between 50 and 70 – that is the average person
in 1900 would have been intellectually disabled by modern IQ norms.
4. The identical twins paradox – past IQ research has shown a close relation
between the IQs of identical twins reared separately; a fact used as evidence for
a genetic basis for differences in IQ. The rapid changes in IQ shown by the Flynn
effect suggest, conversely, that environmental factors have a greater influence
on IQ than genes.
Much of the remainder of the book is then devoted to proposing possible ways to resolve these
inconsistencies, outlining along the way a reconceptualization of "intelligence" and how it might
be better measured and studied.