Show intelligence of twins compared by science physical traits studied the most fascinating phases of twin comparisons are to the majority of us those having to do with intellectual traits writes D cecil rife in the scientific american the relative importance of heredity and environment in mental makeup make up has been for centuries and still is a topic sure to arouse a lively discussion in most groups of civilized mankind have twin studies shed any light on this question considerable research has been done in this field by numerous investigators vesti gators there are certain difficulties cul ties however which are not often encountered in the study of physical traits we cannot be sure whether a given mental test measures only innate learning capacity or whether part of the responses are the result of education and training then too the person tested may or may not respond to the best of his ability there are certain tests such as the simon binet and its revisions which have been thoroughly studied by psychologists over a period of years and have been shown to be fairly valid measures of general learning capacity hundreds of twins reared together have been given general intelligence tests by various investigators the average intra pair difference obtained for identical twins is approximately five points in IQ an insignificant ant figure on the other hand fraternal twins show on an average intra pair differences of from ten to twelve points which is a significant difference the obvious conclusion from such results is that intelligence telli gence is to some degree at least dependent upon genetic makeup make up |