Ed Yong looks at the connection between genes and behavior. Vaughan's framing:
As it became possible to identify individual genes, and more importantly, as automated 'gene chip' technology made this economical, studies began looking at differences between groups of people distinguished by simply having different versions of the same gene.
The idea is to see how a single gene influences behaviour, but because the gene and the everyday effect are so distant (it's like trying to detect the effect of a day of farm weather on the flavour of your lunch) the story often gets mangled in the retelling.