The unborn dog and unborn fish, while they also start together, will branch off and separate at a much earlier period. The unborn of every higher creature reproduces in its structure up to a certain point every bodily feature of every lower creature. And unborn man himself passes over this same road; only, he passes over it more quickly, so as to have more time in the womb. to travel the road that belongs to the human creature alone.

This procedure does not square well with any theory of special creation by which all animals as they are now were created at one and the same time. No man who decided to build a bungalow, a two-story house, a three-story house, and a mansion, at one and the same time, builds four bungalows, adds a story to three of them, adds a third story then on to two of them, and finally turns the fourth into a mansion. Much less would he do this not once, by mistake, but always and intentionally. Evolution makes all this plain and illuminating.

Just as a boy, after he is born, goes in a few years through a sort of savage, and then a sort of halfcivilized stage, i.e., reproduces in himself history that it took his human ancestors after their birth many millenniums to make, so the unborn man goes through in a few months, all those stages which his pre-human ancestors were many evolutionary millenniums in achieving, before man had come onto the scene. But this would remain nothing but a muddle unless they really were his ancestors. In short, scientific men feel compelled to hold the doctrine of evolution because it explains these facts and there is no rival theory which offers any explanation of them. Both these facts, and evolution's explanation of them, are not in the least

abstruse or difficult, but within easy reach of every intelligent man.

I have said that Darwin's contribution to a complete theory of evolution was his principle of natural selection, or the survival of the fittest. Darwin himself did not claim that this was the only factor at work in evolution. In fact, he distinctly disclaimed it. But his followers, more carried away than he was over his discovery, began to ascribe more than he had ascribed to this one factor. They began to talk as if evolution and Darwinism were synonymous. Thomson speaks feelingly of how some misunderstandings of Darwin's position persist;-that Darwin did not discern that natural selection is only selective and not creative, as if he thought it could act without anything to act on; or that Darwin left the question of variability open, 17 or that natural selection in his hands left no part for efforts of the living creature and ignored all inherent tendencies of the organism. But whether Darwin had been misunderstood or had unavoidably given too prominent a place to natural selection, a tendency has developed to revert to the position of Lamarck, who had worked out a theory of evolution before Darwin without the help of natural selection. Lamarck held that use and disuse are the great factors in the development or non-development of organs; that function precedes structure and produces it; and that all qualities acquired by an individual tended to pass at once by the simple process of heredity to his descendants, which was indeed assumed by Darwin and by everyone up to that time. This Lamarckian doctrine is elaborated with much bril

17

System of Animate Nature, vol. II, pp. 440-442.

liancy by Bernard Shaw in the preface to his play, "Back to Methusaleh."

On this matter of heredity, recent evolutionists have gone beyond Darwin, and much knowledge not available in his time has come to light. Darwin, as I said, assumed with all other naturalists of his day, that acquired traits were transmissible. If the parent learned to play the piano before the children were born, or if he were a prize Greek scholar, then the children would find Greek or piano-playing easier on that account. This made the improvement of the race seem a very simple process. But this understanding of heredity has come to be questioned and even denied. All naturalists now say that no clear case of the transmission of acquired qualities is on record. We need not pause to discuss Weismann's experiments in cutting off the tails of successive generations of mice to see if it would make any pronounced difference in the latest born. That experiment seems to merit much of the scorn which Shaw heaps upon it. It was quite superfluous, for a hundred years horses' tails had been docked in England, and from time immemorial women had bound their feet in China.

But in 1882, Weismann made a more significant contribution. With some other naturalists, he had long been convinced that there are two kinds of cells, body cells and germ cells; that the body cells build up the individual structure, and that the germ cells take and hold the characters that belong to the race or the species, and pass these characters on; that the body cells and the germ cells therefore have nothing in common since the body cells have nothing to do with the work of transmission, and the germ cells nothing to do with the work of building up the in

dividual body. As Crampton puts it: "The stream of germ plasm does not flow circuitously from egg to adult and then to new germ cells; but it is direct and continuous, and apparently it cannot pick up any of the body-changes of an acquired nature." 18 In other words it is the cells that have formed and divided and multiplied to make the individual body that undergo any change that may come from the creature's personal history. The other kind of cells, that the individual will pass on to his children as he received them from his ancestors cannot be touched or changed by any of his personal experiences; they will be transferred to his descendants exactly as they came to him. This explains, said Weismann, why acquired characteristics cannot be inherited.

At first this explanation of Weismann won little approval. If acquired characteristics were not transmitted, it was not easy to see how the process of evolution could have made such headway. A partial insight into the method employed was supplied by DeVries in his theory of mutations. Darwin had taught that variation was never more than very slight in degree or kind. From that standpoint, however, it seemed necessary to assume also the transmission of acquired characteristics, or the process of evolution would lag terribly. When belief in the transmission of acquired traits had become no longer tenable, DeVries announced the new discovery in regard to the workings of heredity. Every so often varieties appeared, he had found, which were not merely different from their predecessors, but which "bred true"; i.e. showed no tendency to revert to the type from

18 Doctrine of Evolution, p. 145.

which they had sprung, but began to establish a new type in their own likeness.19

Before DeVries, another great discovery in the field of heredity led to a series of verifying experiments that render somewhat obsolete Darwin's remark that our ignorance of heredity is profound. This is the socalled "Law of Mendel." Mendel also began his experiments with plants. I may state his results in a few words, as follows: 20

If two varieties of sweet peas, one giant and one dwarf, are crossed, the offspring will all prove to be tall. But if these tall descendants of tall and short, fertilize with one another, in their children are both talls and shorts in a definite proportion, three talls to one short. But let the short ones of this third generation fertilize with one another, and you get short sweet peas as long as you may wish to continue the experiment. Remember that in the first generation after you bred the short and the long, there were no shorts at all. But the short blood, so to speak, must have hidden

19 DeVries' discovery of this principle took place in the field of botany. The biologists, I understand, are not universally agreed that it applies in their sphere. If it comes to be widely admitted there, it would greatly help to fill the gap created by the denial of the inheritance of acquired characteristics. For all the capital there is left upon which natural selection can rely is the natural and congenital differences that mark one generation and one individual off from their ancestors. If these differences sometimes take on this character of persistency that DeVries discovered in his Evening Primroses, that would materially quicken the rate of progress in the process of evolution. "There is no hard and fast rule about the origin or nature of mutations; their common features are their brusque appearance, their discontinuity with the parent stock, and their capability of being transmitted intact to a certain proportion of their offspring." (Thomson, System of Animate Nature, vol. II, p. 414.) On mutations, see Thomson and Geddes, Evolution, pp. 124-131. Also, Thomson, System of Animate Nature, vol. II, p. 498. "I am here depending closely, though not verbatim, upon the exposition of Thomson and Geddes in their little book, Evolution, pp. 129-136.