MENTAL INHERITANCE

Sun (Auckland), Volume II, Issue 572, 26 January 1929, Page 6

MENTAL INHERITANCE

PROF. BENHAM LECTURES TO SCIENCE CONGRESS “NOT DEFINITELY PROVED” “In my opinion it is not proved to the satisfaction of biologists that mental qualities are inherited in the same manner and in the same degree as are the physical characters,” concluded Professor W. Blaxland Benham, F.R.S., in his lecture on “The Inheritance of Mental Qualities,” given before the Science Congress last evening. “According to the theories of Galton, who wrote in 1869, mental qualities are inherited in the same manner as physical characteristics,” said Professor Benham. “But in recent years the "subject has been attacked from a new standpoint. It has been dealt with in an analytical manner and in a more scientific way than was possible when Galton wrote in the middle of last century.” He explained that the child may inherit various parts of the physical make-up of his ancestors and relations, and described, with the aid of lantern slides, the formation of the embryo and the stages through which it passes, showing that the human embryo, in its early forms, is quite indistinguishable from that of a pig, a rabbit or a dog. Nevertheless, the animal into which the embryo was destined finally to develop was always unerringly chosen. He then went on to give a review of Mendel’s work in establishing the principles of physical hei'edity. By means pf experiments with tall and dwarf peas, Mendel proved that dominant stocks crossed with recessives produce a hybrid, which in turn breeds a number of true-breeding recessives a number of true-breeding dominants and a number of hybrids, which have the appearance of dominants, but which breed in the same way as the first hybrid. Mendel further proved that the proportion of true-breeding recessives to the number of apparent dominants is as one to three. Professor Benham demonstrated that the Mendelian theory applied also to human beings, taking as his example the colours of the eyes in parents and children. He then showed, by means of slides, something of the cell-action that brings about these hereditary changes. He described how a single germ cell splits into two parts in order to unite with a similarly divided germ cell of the opposite sex, so as to form one complete germ cell of the new animal. “It is during the formation of these new germ cells that the fundamental things relating to heredity take place.” FAMOUS INSTANCES The professor then went on to the subject of mental heredity. “It is assumed, with every probability of truth,” he said, “that the physical characteristics in man are represented in the chromosomes (the inner miclei of the cells), just as in the case of animals. But when we consider the mental qualities we are met at once with tremendous difficulties, for we have no analogy to work with, since mental qualities in the lower animals are either non-existent or have not been adequately studied from this point of view.” Quoting diagrams prepared by Galton, he gave examples of heredity in distinguished families. The grandfather and great-uncle of Charles Darwin, the great biologist, had been comparatively distinguished men. Of their five children only three had done anything in the world. Of these three there had been 11 children, and again only three, of whom Charles Darwin was one, had been heard of, and those three had a total of 21 children, of whom 18 faded into obscurity. From this large number of negligible descendants, Professor Benham deduced that the principles of physical heredity could not apply to mental development. He also drew attention to the fact that all the children who gained Dime did so in widely differing spheres of action from that of their parents—again showing the difference between physical heredity and mental development, since physical heredity tends to show a great similarity rather than a difference between parent and child. “According to Havelock Ellis,” he concluded, "environment and opportunity has far more to do with talent and with the choice of a profession than has heredity.” He then turned to the subject of feeblemindedness. It ivas by no means certain, he said, that this had any more to do with heredity than had talent. It was probably due, in large part, to environment, just as talent was. “But in no case can we assert with certainty that the quality of ability or feeblemindedness is due to heredity, nor can we say to what degree heredity plays a part or to what degree environment. "In my opinion it is not proved to the satisfaction of biologists that mental qualities are inherited in the same manner and the same degree as are the physical characters. The physical characteristics of man, as of the lower animals, are the resultant of the interaction of heredity and environmental stimuli, and so it is with mental qualities.”