Unit 4 Twins: An Early Study PDF

‫ קורסים מקוונים ללמידה עצמאית‬:‫אנגלית אקדמית‬ ‫ בסיסי‬:‫רמה‬ Unit 4: Twins: An Early Study :4 ‫יחידה‬ TWINS: AN EARLY STUDY Studies of twins have served a...

‫ קורסים מקוונים ללמידה עצמאית‬:‫אנגלית אקדמית‬ ‫ בסיסי‬:‫רמה‬ Unit 4: Twins: An Early Study :4 ‫יחידה‬ TWINS: AN EARLY STUDY Studies of twins have served as valuable tools for examining the complex influences of heredity and the environment on the development of a wide range of human characteristics and behavior. 1 The first scientific attempt to study the mental abilities of twins was made by Francis Galton. Galton was interested in twins because of the light that a study of them might throw on the relationship between heredity and environment. His chief object was to determine whether or not very similar twins become unlike as a result of a difference in environment, and whether, on the other hand, twins who were unlike in early life become more similar as a result of living in the same environment. Galton believed that there were two distinct types of twins, one of which developed from a single ovum and the other from two separate ova. The evidence on which Galton based his conclusions consisted of reports of the characteristics of the twins which he obtained at second hand through correspondence. 2 By this means Galton obtained information concerning thirty- five pairs of twins who were reported to be so closely similar that is was difficult to distinguish one from the other by their appearance. He also obtained reports concerning twenty pairs who were not so closely similar and who were thought by their friends and relatives to be no more alike than are brothers and sisters in general. It is probable, in the light of our later evidence, that the twins of the first group were 1  ‫ קורסים מקוונים ללמידה עצמאית‬:‫אנגלית אקדמית‬ ‫ בסיסי‬:‫רמה‬ Unit 4: Twins: An Early Study :4 ‫יחידה‬ chiefly identical twins and those of the second group chiefly fraternal twins. 3 Most of the facts which Galton obtained regarding the similar twins relate to their very close resemblance in physical characteristics. For example, both members of seven of the pairs suffered from the same physical ailment. Both members of another pair developed a toothache in the same tooth at about the same time, and each had the tooth extracted. Both individuals of another pair were afflicted with ophthalmia* and had attacks 0F at about the same time even though one was in Vienna and the other in Paris. There were two cases of similar insanity. Eleven pairs said that they had similar association of ideas. For example, one would begin a sentence and the other completes it. On the other hand, there were differences in disposition noticed in the case of nineteen pairs of very similar twins. In some cases the differences in disposition were caused by a serious illness or an accident. Galton reported that illness or accident was the only cause which appeared to be adequate to make similar twins unlike. The ordinary differences which are characteristic of current life did not perceptibly affect their likeness. 4 In contrast to the similar pairs, those who were unlike at the beginning did not become more alike as a result of their similar environment. Little detail was reported concerning the dissimilar twins except that some reports of their differences indicated that they were no more alike than are brothers and sisters. Galton concluded that environmental differences, such as are to be From: H. Newman, F. Freeman & K. Helzinger, (1937). Twins: A Study of Heredity and Environment. Chicago: University of Chicago Press, pp. 4-5. 2  ‫ קורסים מקוונים ללמידה עצמאית‬:‫אנגלית אקדמית‬ ‫ בסיסי‬:‫רמה‬ Unit 4: Twins: An Early Study :4 ‫יחידה‬ found in the same community and at the same time, produce slight change in the individual’s physical and mental makeup and that physical and mental characteristics are determined chiefly by inborn nature. It is to be noticed, however, that Galton's evidence is much stronger in relation to physical traits than it is in relation to mental characteristics and abilities. It should be noticed further that the differences in environment which were brought to bear upon the similar twins did not appear until adult life. 3