Fraternal Twins – +. 60
Brothers and Sisters – +. 50.
Siblings – +.40
Cousins – +. 25
This study does not reflect the superiority of heredity over the environments since the factor of environments has been dwarfed and since the increase of blood relationship also increases the similarity of environments.
(2) L.M. Terman:
Found that out of 62 members in the Hall of Fame. 221/2% were related to 643 gifted children identified and studied in California.
Found from his analysis of 977 men of genius who were found to have 535 eminent relatives, whereas, 977 average men had but four relatives who were eminent.
This data also does not endorse the view of either the superiority of hereditary or environments. Granted that the above men had better heredity but they also had better environments.
(4) Arnold Gesell:
From his experiments on co- twin control found a striking similarity in their emotional expression, in mental growth, and in certain motor acquisitions. He also found remarkable similarity even if one of them had undergone training e.g., stair-climbing or vocabulary development.
Found that regarding the vocabulary study “The twins are sub-average (mentally) and not all the special training was able to bring them up to the average vocabulary of children three and one-half months younger than they.”
So it appeared, therefore, that “inner growth” or maturation” sets levels that special training did not enable children to transcend.
(6) G.C. Schwesinger:
Studied ten pairs of identical twins reared apart from birth or from infancy and brought together and studied at maturity.
In Six Pairs —no difference.
Two Pairs —Difference of 12 Points.
Remainder—Difference by 15 or 17 Points.
Now-a-days it is commonly believed that I.Q. can be used to predict future individual development.
From his study of Glasgow children concluded that dull children come from large families. Catell also endorsed this view.