Numerous statistical studies of the inheritance factor indicate that insanity is gradually increasing. This increase has been attributed not alone to the more intense strain of modern life, but also to alleviation or temporary cure of mental derangements by appropriate treatment, thereby giving the mentally unfit a greater chance for procreation.
In contrast to these notions stands Mott's1 "law of anticipation," derived from the study of a series of 217 pairs of father and offspring and 291 pairs of mother and offspring in which two or more members of the same family had been inmates of London county asylums. He found insanity appearing in 2 per cent, of the fathers and 4 per cent. of the mothers before 25 years of age, whereas among the offspring, 44 per cent, of the cases occurred before 25 years of age. The average age of onset of insanity was 50 years in
THE "LAW OF ANTICIPATION". JAMA. 1915;LXIV(21):1767. doi:10.1001/jama.1915.02570470051018