THEORIES ON HEREDITY

Evening Star, Issue 23679, 12 September 1940, Page 4

THEORIES ON HEREDITY

THROWN OUT BY PSYCHOLOGIST Striking at what he calls “ the most damaging of superstitions,” Dr Knight Dunlap, professor of psychology on the Los Angeles campus of the University of California, says that one of the major duties of psychologists is “to explain in detail the complete lack of scientific foundation for the popular theories about heredity, which, unfortunately, are still endorsed by some text books,” says ' the ‘ Christian Science Monitor.’ Dr Dunlap, for 30 years professor of psychology at Johns Hopkins before coming to the campus here in 1930, is, himself, the author of a number of college texts and other books on psychology. Describing some of the myths and nostrums which “ skulk in the: pages of supposedly scientific books on psychology,” Dr Dunlap said that “ the

Kallikaik phantasy has been laughed out of psychology, along with the even more appalling legends of the Kams and the Jukes; but the theories involved‘in them still linger in popular superstitions, endorsed by many writers, along with other popular beliefs about heredity, and do definite damage to young persons who take the theories seriously.” He described the damaging results of fear, in the minds of young men and women, deluded by the thought that they are victims of some imaginary hereditary ailment. Dr Dunlap cited the case of a young woman who had brought to him an elaborately drawn family tree, around which she had built her fears that she had inherited a mental disorder. Her fears subsided, however, when it was pointed out that the branch of the family tree on which she had hung most of her theories came through an aunt by marriage and that no one has ever believed that ailments could be inherited that wav. Speaking in language shorn of laboratory terminology, Dr Dunlap bluntly* declared : “ For a person who discerns an occasional nut or two on his family tree the chances that he will

have a nut for a child are, so far as is now known, no greater than for the persons who don’t happen to find any nuts on their trees.” The tendency to-day is for psychologists to revise their books along Jess arbitrary lines, to discard conclusions of which they were “ positive ” only a few years ago, and even to admit that they “ know nothing, as yet, about the modes or details of inheritance of important traits,” Dr Dunlap pointed out. “ Hasty inferences from traits of fruit flies and potatoes to human traits,” he said, “ have not been useful. Scare data which has been assembled to prove the fatal heredity of mental diseases and of feeble-minded-ness has been gathered by the toofamiliar method of selecting the data which agrees with one’s theory, while ignoring cases which would not support it. “Some of the data which impresses the public most was gathered by untrained persons, who were not able to tell whether an individual is feeble-minded or not.” To substantiate what he said, Dr Dunlap cited other loading authorities on psychology, and recent findings by Dr Abraham Myerson, eminent Boston psychologist.

To further illustrate fallacious beliefs about heredity, Dr Dunlap cited superstitions that have been built up around the eye-colour doctrine that there are two classes of eyes, often called blue and brown, and that it is not lawful, in the Mendelian sense, for the child of two blue-eyed parents to have brown eyes. The eye-colour superstition is of origin somewhat less ancient than some of the other fallacious theories about heredity, and only recently has it begun to be eliminated from text books. “ Actual study of eyes shows at once that eye colour in a mixed population such as that of the United States or European countries is not an * all-or-fnone ’ matter,” says Dr Dunlap, “ but the colourations of the iris are mosaic patterns involving usually more than two colours. The brown-eyed child who is worried about his parentage can resolve his doubts by examining the eyes of his putative parents with a good reading glass in good daylight. Eyes are mixed so generally that the chances that the brown-eyed child will not find some brown areas in the eyes of his parents arc so small as to be negligible.” _ Speaking of certain defects which

are supposed to “ run in the family,’* Dr Dunlap said that he had found many of those he had studied as “ no more significant than the cases of vegetarian, ism, poverty, Republicanism, or Presbyterianism, which also ‘ run in families.’ ’’ He cited specifically a popular but erroneous belief that common forms of deafness are congenital. “ The real problem of heredity,” says, Dr Dunlap, “ is not done away with, however, but it is revealed as so complex that its principles have -little in common with the popular doctrine* handed down from the past.”_ Summarising his conclusions, tjia University of California psychologist' declared: “ I must insist that at the present, time one ,of the major duties of psychologists, in the service of society, is to combat the popular super- ) stitions about human heredity to point out that we know nothing, as yet, i about the modes or details of inheritance of important traits, and that it is our duty, further, to explain in detail > the complete lack of scientific founda--1 tion for the popular theories, which, nni fortunately, are stil endorsed by some i text hooks. In this way, we can assist the prophylaxis againsU the most damaging of the superstitions.■