The science of life : fully illustrated in tone and line and including many diagrams

wdS A

ESSENCE OF THE CONTROVERSIES ABOUT EVOLUTION

There may be a thousand outer influences working upon the minute elements in reproduction of which as yet we know nothing, from obscure chemical factors in the food to electromagnetic radiations from outer space. There may be a thousand subile selective influences rejecting this variation and preserving that. Here again our duty will be to sum up the known facts and views and leave the conclusion to the reader.

We have then still active in the biological field (1) the élan-vitalist, (2) the Neo-Lamarckian, and (3) the Neo-Darwinian ; three distinctive schools as to the origin of variations. They are by no means mutually exclusive. Any follower of either school may attach more or less importance to the variational drive or conversely to the action of Natural Selection, and Orthogenesis may be used to account for more or less or none of the changes that have occurred. In a world of earnest workers these various shades and blending of opinion are hotly debated. Biologists can be as sensitive to heresy as theologians or any other sort of men in deadly earnest, and it is quite easy for dullminded or dishonest controversialists delving in the literature of the subject to clip out such phrases as that ‘‘ Darwin has been disposed of,’? or that “ Natural Selection is inadequate,’ and pretend that a conviction or refutation in some particular is an absolute reversal of view. But, indeed, no such collapse has occurred. Difficulties in ‘‘ accounting for” variation are minor difficulties in face of the invincible facts of the evolutionary process. Every day the form and details of Evolution, the life process, are seen more clearly, solidly, certainly, and coherently.

We need scarcely point out to the interested reader how temperamental disposition and philosophical and moral preoccupations may dispose men’s minds towards one or other of the three types of opinion. This possibility gives this branch of our subject an interest and excitement far beyond the strictly biological field. There is something cold and stern, very attractive to a certain hard, clear type of mind, in the Neo-Darwinian attitude. There is something heroic in the obstinate advance of Orthogenesis. The Neo-Lamarckian view appeals most to those combatant spirits who would figure man in a Promethean and finally hopeful conflict with the universe ; again, the mystic and the believer in a continually directive divinity incline very naturally towards the hidden upward urgency of the élan vital. For him it becomes the finger of God. It is a return towards the idea of creation, as

Bergson’s popular and_ attractive phrase Creative Evolution reminds us.

There remains one other temperamental type which has found expression in these discussions, and that is the brilliant sceptic as typified by the late Professor William Bateson. He accepted the fact of Evolution, if only on the paleontological evidence, but, as the outcome of a life spent largely in the study of variation and especially of Mendelism, he developed an increasing inability to satisfy himself how any progressive variation could ever occur. He crowned his scientific career by various lectures and addresses in which he reiterated his imaginative failure. This type of agnosticism was probably the negative aspect of a passionate and unquestioning faith in the implacable unteachableness and integrity of certain Mendelian units of heredity we shall presently describe and discuss. Later work has removed much of the point of his criticisms.

§ 2 Method of Treatment

The threefold author of this work must admit that the writing and arrangement of this Book have cost him more trouble and effort than any other portion of the undertaking. A word about his difficulties may be of help to the reader who is steadily following this exposition of the Science of Life and who has now to read what has been so painstakingly written.

The broad facts and the consequences of inheritance are of universal interest; the minute study of the mechanism of individual development and variation is, on the other hand, very obscure, outside everyday experience, and can easily be made very complicated. Yet the broad questions we have posed in the previous section are only to be grasped soundly after the nature and bearing of this minute mechanism have been understood. The problem has been to give a full and exact account of this difficult subject, an account which a lawyer, let us say, or a schoolmaster or anyone of general intelligence but without special biological training, might be expected to follow with interest and understand, and at the same time not to confuse, weary and defeat the natural widespread curiosity about these things.

We decided to eliminate every avoidable technical term, and those we have found unavoidable—genes, germ-plasm, chromosomes, for example—we have explained with sedulous care and much mutual criticism. Much of the current literature of heredity resorts to

265