Many of our psychological traits are innate in origin. There is overwhelming evidence from twin, family and general population studies that all manner of personality traits, as well as things such as intelligence, sexuality and risk of psychiatric disorders, are highly heritable. Put concretely, this means that a sizable fraction of the population spread of values such as IQ scores or personality measures is attributable to genetic differences between people. The story of our lives most definitively does not start with a blank page.

But exactly how does our genetic heritage influence our psychological traits? Are there direct links from molecules to minds? Are there dedicated genetic and neural modules underlying various cognitive functions? What does it mean to say we have found “genes for intelligence,” or extraversion, or schizophrenia? This commonly used “gene for X” construction is unfortunate in suggesting that such genes have a dedicated function: that it is their purpose to cause X. This is not the case at all. Interestingly, the confusion arises from a conflation of two very different meanings of the word “gene.”

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