yet has given us even a conceivable explanation, much less a possible one. It is a problem that will probably always remain shrouded in mystery, although no doubt the human intellect will always be trying to solve it.

And now, ladies and gentlemen, I have explained to the best of my ability the scope and limits of Darwinism. All through the lecture I have felt the difficulty of expounding clearly so vast a subject in so short a time; and I could have wished it had been placed in other hands. It was necessary for me to be concise, in order not to leave out any important point; and if at times I have been dry and obscure, I will ask you to remember this necessity for condensation, and to believe that I have tried to make my language as plain and as intelligible as possible.

LECTURE II

THE NEW DARWINISM

ELEVEN years ago I gave a lecture to the members of this Institute, in which I explained what was then understood as Darwinism; and I have now undertaken to try to explain the modern views held by Darwin's followers. Unfortunately it is a subject which, at the present time, is in a very confused condition, owing to the innumerable irrelevant issues that have been raised around it; but, when all the husk has been stripped off, the new Darwinism will be found to be a simple affair, easily understood.

This confusion is largely due to its history; for the new Darwinism did not come upon us in a flash, as did the old, but has been gradually assuming shape for many years.

In 1868 Moritz Wagner read a paper to the Royal Academy of Munich, in which he maintained that, without the separation of a few individuals from the rest of the species, natural selection could not act, and that these individuals must always have been isolated by geographical barriers. His thesis could not be upheld on either point, although it brought the importance of isolation prominently forward; and we may place the birth of the new Darwinism in November, 1886, when Dr Romanes' first paper on physiological selection was published by the Linnean

Society of London; for this contained a new idea. From that time it has gone on gaining coherence; and last year [1897] it received its latest development in the third part of "Darwin and after Darwin," also the work of Dr Romanes.

This new Darwinism has not destroyed, or in the least damaged, the old. Indeed, it is not antagonistic to it in any way. It is merely an addition; but one of great value; for, as I shall explain at the end of the lecture, it enlarges much our conception of the great scheme of nature. The doctrine of organic evolution, which was firmly established by Darwin, is now regarded as a fact by all scientific men; and his theory of natural selection, as a method of progressive evolution, is accepted, to a greater or less degree, by most naturalists. Darwin himself, as I reminded you in my former lecture, never thought that his theory was complete. He always taught that natural selection had been the main but not the exclusive means of modification. He knew that something was wanting; and it is that something which the new Darwinism attempts to supply.

THE NEO-DARWINIANS AND THE NEO-LAMARCKIANS

The Neo-Darwinians, as we are sometimes called, accept Darwin's teaching, and supplement the theory of natural selection with methods of isolation, which had been either overlooked or had not been brought into sufficient prominence by Mr Darwin. Those naturalists, who hold the opinion that natural selection has been of little importance in evolution, call themselves Neo-Lamarckians; for they think that the

teaching of Lamarck is nearer the truth than that of Darwin. And, in order that we may set out with clear notions of the differences between these two schools, it will be necessary for me to remind you, shortly, of the leading points in each; although I do not intend to go again over quite the same ground as I took you before.

The first great problem to be solved in organic evolution is the fact of progression upwards, from the simplest organisms to the most complicated. Progress implies a directive or determinative agency; and the question which presents itself is this:-Are the variations definite, that is, in a single direction, as they arise ? Or are they indefinite, that is, in many directions; and has progress been secured by some subsequent selection of certain variations to 'the exclusion of others? In other words, can we see the elements of progress in the variations themselves? Or must we look for progress to some process which comes into operation after the variations have been formed?

Now Lamarck's theory is one of definite variation. He taught that progress was due to an internal tendency towards progression, combined with the action of external conditions on the organism, and with the more or less frequent use of the different organs of the body, due to different wants, which were caused by changed habits. For example, he supposed that the constant stretching of the toes of the otter in the act of swimming had caused the skin between the toes to enlarge; that constant running had made deers and antelopes fleet; and that constant stretching of the neck of the giraffe had made it grow.

The variations that arose in this way must therefore be definite or progressive, and must have been acquired after birth. He had only to

assume that these acquired characters were transmitted to the next generation, and his theory was complete. The NeoLamarckians agree that progress has been mainly— although perhaps not exclusively-secured by the inheritance of post-natal variations, which have arisen, either through the attempts of animals and plants to adapt themselves to external conditions, or by the direct action of external causes on the individuals. The rest they refer to natural selection, the idea of an internal tendency towards progression being generally discarded.

Darwin taught that post-natal variations, due to the direct action of external conditions, are seldom, if ever, transmitted; and he held that progress has been chiefly due to the picking out of certain indefinite variations by the process of natural selection. Lamarck's theory, therefore, includes both the origin and the preservation of variations; for the variations are preserved by the conditions which called them into existence; while Darwin's theory relates to the preservation and development of variations only, and makes no attempt to explain their origin. Even with reference to the preservation of variations, the two theories are not exactly antagonistic; and they might possibly flourish side by side; for natural selection, although favourable to the hypothesis of indefinite variation, is not opposed to that of definite variation. It is only a process of picking out useful variations, no matter how they have arisen.

It may be thought that it would be easy to test

E