"Our calculations suggest that anorexia is under weaker negative selection relative to schizophrenia and autism," the authors said.
Substance abuse was present in 55,933 patients, who had a total of 81,592 siblings. The fecundity rate was significantly lower in both men and women (FR, 0.78 and 0.93, respectively). Siblings had significantly more children than the general population (FR, 1.03 for brothers and 1.05 for sisters).
"Our findings suggest that this increased fecundity in siblings almost entirely accounts for the cost to affected individuals, with only a slight decrease in the frequency of these individuals’ genes predicted each generation. Considering that most drugs are a new environmental exposure when seen from an evolutionary perspective, it is possible that there has been insufficient time for selection to act on risk alleles. ... It has also been suggested that substance abuse is associated with risk-taking behavior in both sexes, including sexual risk taking."
The study was funded by the Medical Research Council of the United Kingdom. One of the coauthors reported having received consulting fees and honoraria from GlaxoSmithKline and Lundbeck.