Education by Wireless

Radio Record, Volume II, Issue 52, 12 July 1929, Page 10

Education by Wireless

The Mechanism of -Evolution

"THE following is a summary of the W.E.A. lecture to be given from 4YA on July 16, at 7.30 p.m. :-- } (4) Evolution Independent of Environment. The principle of Natural Selection and the mechanism of evolution suggested by Lamarck explain how new species may evolve by the reaction of an organism to its environment. Yet some changes of a similar nature appear to have taken place both among plants and animals, as a result of obsecure processes the cause of which we do not yet know, but which we do know to be unconnected with the influence of environment. The Dutch botanist Hugo ‘de Vries was the first to observe that at certain times ‘there may suddenly spring up new characters apparently arising from sudden changes in the germinal material, and that such characters once they are developed continue to be inherited according to the normal laws of heredity established by Mendel. Such new eharacters he termed mutations, and the theory of evolution which he put forward is called the mutation theory. The work of De Vries was founded upon observations of a certain primrose. He noticed that in each generation, among thousands of individuals, there were a very small percentage of mutants, including, for example, types prec entaien ee taarane — ee 2h eee

with a smooth leaf, crinkly leaf, large flower or small flower, and that such types if segregated, bred true to type, thus perpétuating the new form. In such mutants De Vries believed he had found the raw material for evolution. But even granting that mutants commonly occur in nature, there must still be some such process as natural selection in operation if some of the new forms are to be perpetuated and others eliminated, ie. if evolution is to take place. Hivolution implies something more than the mere production of a new type in one generation: it involves also the perpetuation of the type through successive generations, and if this is to be effected other forms with which the new type might hybridise must be cut out. It appears probable, however, that mutations are not nearly as frequent as De Vries supposed, and probably mutants constitute only a very small proportion of the innumerable variations upon which natural selection is working in the process of evolution. It will be noticed that the changes which occur in the mutations of De Vries occur at random, in any direction. On the other hand, students of the fossil record cannot but be impressed with other changes which seem to have taken place independent of environment, and yet which have followed some particular direction.

It would appear that sometimes a group of organisms may have latent within them the tendency to evolve along,some special line; and that once evolution of this sort starts it gathers, as it were, a momentum which may carry the process of structural change far beyond.the limits of usefulness, until ultimately the extinction of the organism may be brought about by its own power to evolve along lines which have become harmful to its existence. Evolution of this sort has been termed orthogenesis and its operation is one of the most discussed problems of modern palaeontology. One of the commonest types of orthogenetic tendency is the potentiality possessed by many animals to secret a heavier and heavier living skeleton. That such a tendency may be carried far beyond the limits of usefulness is clearly seen in the case of many of the

reptiles of the later part of the Mesozoic Bra, in which there was a most_ extraordinary development of external bony armour in the shape of horns, plates and spines, of enormous size and weight. It is again exemplified in the great thickness and weight of the shells of jnany of our fossil oysters, which no sooner attained this great size than they became extinct. . In conclusion, it seems to the modern scientist and to the geologist especially, that evolution is an extremely complex process in which a number of factors of varying importance are all operating. While Natural Selection is undoubtedly the most important of these factors, it is nevertheless probably assisted to a considerable extent by La-

marck’s principle of the direct action of environment. Mutation and hybridisation also have probably contributed to some extent in supplying some of the material upon which natural selection has worked, while impressed upon all these is the mysterious process of orthogenesis working changes independent of environment, the cause of which we nave still to discover.