Some supporters of heredity have based their investigations on the following evidences:

(i) Unequal intelligence levels of individuals of different occupational groups; (ii) Unequal intelligence levels of difference: racial categories; and (iii) The study of famous families of Edwards and degenerate families of Jukes.

(F) Unequal intelligence levels of individuals of different occupational ‘groups. Some supporters of heredity have drawn our attention towards considerable differences between the intelligence levels of different occupational groups. For example, in one of the studies it has been observed that the children of professional parents had an average I.Q. (intelligence quotient) of 116; those of semi-professional and managerial classes 112; clerical skilled trades, and retail business 107.5; semiskil1ed minor clerical occupation and business 105; slightly skilled 98; and finally the children of laborers, urban and rural farmers, 96. These differences in I.Q. were attributed mainly to heredity.

(ii) Unequal intelligence levels of racial categories such as Whites and Negroes. In America, a number of psychological intelligence tests were administered to the Negroes and Whites. In these studies of comparative intelligence the Whites faired better than the Negroes. For example, the tests applied to army recruits during World War I had revealed the average mental age of Negroes as 10.4 years and of the Whites as 13.1 years.

(iii) The Study of the families of Edwards and Jukes. The study of the families of Edwards and Jukes as an evidence in favor of heredity is quite fascinating. In America, towards the end of the 19th century, some 1391 descendants of Jonathan Edwards were identified out of which more than 295 were college graduates and among them 13 came to be college presidents or principals and one a vice-president of America. The records showed that there were no convicted criminals among them.

As against the above, in 1887, there were identified 1200 descendants of a certain ‘Juke’ who was born in New ‘York in 1720. Of these, 440 were physically defective or diseased, 310 were paupers, 130 convicted of crime, and 7 condemned as murderers. It was concluded that heredity and not environment, was the decisive cause of the difference of behavior in these families.

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