Familial Aspects of “Neuroticism” and “Extraversion”

Abstract

There is a good deal of evidence that hereditary factors make some contribution to determining a predisposition to neurotic illness, and some of the relevant literature has recently been reviewed by one of us (Slater, 1964). Raised incidences of neurotic illnesses and neurotic traits of personality of a like kind have been found among the first-degree relatives of obsessional neurotics, anxiety neurotics and persons diagnosed as suffering from hysteria. The evidence is much stronger in the case of the first of these types of illness than in the last. Such observations do not absolutely require a genetical explanation. It is possible that the similarities shown by relatives are not caused by their blood relationship, but by similarities in such aspects of the environment as early upbringing, social milieu, family tradition, etc. However, these findings do suggest that, if there is a genetical contribution to the personality traits which are associated with neurotic illness, this will most likely be due to a number of genes, additive in their action. This again would lead one to expect to find continuous variation between individuals in the degree to which they show such personality traits, and in our view the available evidence supports a multidimensional mode of variation.