The Annual Register 1914 / A Review of Public Events at Home and Abroad for the Year 1914

by Anonymous

M. G. T.

Zoology.

Professor Arthur Dendy, President of the Zoological section of the British Association, which this year met in Australia, took as the subject of his address "Progressive Evolution and the Origin of Species." Darwin and Wallace established the main principle of evolution, but at the present time there is still great diversity of opinion among expert biologists as to the means by which organic evolution has been effected. Darwin and Wallace held that species originate under the influence of "natural selection"—the selection by nature of fit variations. Later, De Vries brought forward the view that species arise by sudden "mutations" or sports, and thus not by gradual changes, and the well-known Mendelian Professor Lotsy holds that all species originate by crossing. At present, it is mainly due to the impetus gained by the introduction of experimental methods that there exists so much difference of opinion. Professor Dendy's address was an endeavour to take a general survey of the situation.

A theory of organic evolution should account for the following principal groups of facts: (1) "that on the whole evolution has taken place in a progressive manner along definite and divergent lines; (2) that individual animals and plants are more or less precisely adapted in their organisation and in their behaviour to the conditions under which they live; (3) that evolution has resulted in the existence on the earth to-day of a vast number of more or less well-defined groups of animals and plants which we call species."

Professor Dendy seeks to explain the fact that organisms throughout nature show a slow progression by the "law of the accumulation of surplus energy." From Jennings's work on the "Behaviour of the Lower Organisms" one is led to the conclusion that the lower animals learn by experience to make the appropriate response to stimuli without having to pass through the long process of trial and error. They are thus able to perform a given action with less expenditure of energy. The same is true for higher animals, and the power of profiting by experience is apparently a fundamental property of living protoplasm. Jennings speaks of this property or principle as the "law of the readier resolution of physiological states after repetition," and this law probably lies at the root of progressive evolution. As a corollary to the principle enunciated by Jennings, the "law of the accumulation of surplus energy" would follow. In the organism or in the egg cell, the oftener the process of absorbing food-material is repeated, the easier does the process become, and thus the organism tends to accumulate surplus energy in excess of its own needs. Professor Dendy lays emphasis on a progressive accumulation of potential energy by succeeding generations of animals and plants—each generation having a slightly greater amount than the previous one—and that by means of this cumulative energy, structural progressive changes are evolved, or in other words there is progressive evolution. He holds that there takes place in nature in the stricter sense something similar to that which seems to occur in human life, when certain families rise in general well-being and prosperity through the gradual accumulation of capital in successive generations, and in virtue of this handed-on capital each later generation starts with an advantage over the previous one.

Professor Dendy also holds that the law of recapitulation, which may be stated thus, that the life-history of the individual is a recapitulation of the life-history of the race, is a logical necessity if evolution has taken place. Leaving out, for the present, the complication introduced by the union of two germ cells of separate sexes, the behaviour of the germ cell during development is conditioned by two factors, namely its own constitution and its environment. It is now accepted that the living matter of the germ cell is continuous from generation to generation, and given the same environment, the germ cell should develop in a similar manner in succeeding generations, but with a difference arising from the "law of the accumulation of surplus energy." The organism developing from the germ cell will have a greater capacity for responding to stimuli—it will be a slightly more capable and efficient being in each successive generation. The organism must repeat in its life-history the stages passed through by its ancestors, because at every stage there is an almost identical organism exposed to the same environment, but there will be an acceleration in the individual life-history owing to the cumulative storing of potential energy.

As in human life, however, an organism really inherits from its parents two things, namely, living protoplasm with potential energy and an appropriate environment. When we say that an organism inherits a particular character from its parents, we really mean a special feature which is handed on if the appropriate environment is also present to bring out that character. The inheritance of the environment is as important as the living protoplasm, for in each life-history an animal is capturing and assimilating from the environment handed down to it from its parent.

The response which an animal makes to its environment is probably not merely purely mechanical, for Jennings has pointed out that in the case of the lower organisms, the response to stimuli is to a large extent purposive, namely that the organism has the inherent capacity of selecting those modes of response which are best for its own well-being. Those responses to stimuli may result in change of structure, and thus the evolution of the body will be adaptive and follow along definite lines. One has, however, to remember that while the germ cell may be slightly different in successive generations, the environment is also changing in these generations.

In trying to understand evolution and the doctrine of recapitulation by the individual of the life-history of the race one must proceed slowly and by single steps, for there is no difficulty in understanding how any particular stage is related to the corresponding stage in the previous generation, but the whole series of changes is simply the sum of successive terms.

Space does not permit a complete review of Professor Dendy's contribution. Its most important part seems to be the "law of the accumulation of surplus energy." The complications introduced into the problem by the union of two cells of different sexes Professor Dendy regards as less important than is generally held, as the parents must have been alike in main respects or they could not have interbred. He also recognises the very important recent work on "mutation" and "hybridisation" from the point of view of heredity, but regards the unit characters arising by mutation and interchanged by hybridisation as chance characters due to chance modifications of the germ-plasm, and having comparatively little influence upon the general course of evolution. The characters inherited in the Mendelian manner are apparently non-adaptive, and with no particular value in the struggle for existence. Probably the nucleus of Professor Dendy's position may be found in the following quotation: "Surely that much-abused philosopher, Lamarck, was not far from the truth when he said, 'the production of a new organ in an animal body results from a new requirement which continues to make itself felt, and from a new movement which this requirement begets and maintains.' Is not this merely another way of saying that the individual makes adaptive responses to environmental stimuli?" As a counteractive to the foregoing, however, the reader may be referred to Professor Bateson's "Problems of Genetics," in which he writes: "When ... we contemplate the problem of Evolution at large, the hope at the present time of constructing even a mental picture of that process grows weak almost to the point of vanishing."