T

he causes of variation in human potential— for attributes like intel-
ligence, and educational and occupational achievement— are always
in ter est ing. Th e expression “fulfi lling our potential” is widely used
and implies destinies already laid down, with variable, but defi nite, limits.
Moreover, the causes of variation really matter: perceptions of some-
one’s— a child’s— potential can seriously prejudice how the individual
might be treated by others and by our institutions. As every one knows,
that is why a nature- nurture debate has smoldered around the issue for
hundreds, if not thousands, of years.
Th ank goodness, then— you might think— that modern scientists are,
according to widespread reports, settling the issue at last. Th ey can tell us
about the real nature of intelligence, and even mea sure it with IQ tests.
Th ey have revealed, in remarkably exact proportions, how individual
diff erences are due to diff er ent genes. Th anks to the brilliant technology
that sequenced the human genome, we are told that scientists are now even
identifying the genes responsible for that variation. Th ey are also showing
how those genes—in interaction with environments— shape our brains
to determine our levels of intelligence (and diff erences in them). What is
more, those scientists might soon be able to design genet ically informed
interventions in schools to help those not so well endowed, or even target
specifi c genes to boost IQ and give the world more geniuses. So now, at last,
we can put that heated nature- nurture debate behind us once and for all.
However, there is something wrong with that scenario. None of it is true.
Th e advances turn out to be more hy pe t han rea l it y. Th e fi ndings are crude,
based on assumptions that are de cades old and long since criticized as

PREFACE

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