"For instance, in the realm of psychiatry there is no known gene or clear genetic variants for around 97% of all the mental disorders now contained in the current DSM and ICD. And even where genes may be implicated in disorders like bi-polar disorder and schizophrenia, research now reveals such mind-boggling complexity that nothing definitive can be said about ‘this causing that’.

A central complicating factor is our growing understanding of epigenetics. Modern genetics now broadly accepts that it is virtually impossible to understand how our biology works outside the context of our environment. To put the new genetics in the simplest terms, virtually no neurological and psychological disorders have been demonstrated to result from the mutation of a single gene. Rather they are now known to involve molecular disturbances that implicate multiple genes and the signals that control their expression.2In other words, the popular idea that so-and-so gene causes so-and-so mental trait has been surpassed by the notion that it is interactions between our genes and their environment that actually shape us."

(emphasis added.)

No known biological causes. / CEP / 2014.