A large proportion of the public are not aware of the amount of experiment and observation carried out by the great naturalist whose memory was honoured by a splendid ceremony at the University of Cambridge in the summer of 1909. There are, I am sure, not a few who are under the impression that Darwin, sitting in his study or walking round his garden, had “a happy thought,” namely, that man is only a modified and improved monkey, and proceeded to write an argumentative essay, setting forth the conclusion that mankind are the descendants of some remote ancestral apes. Of course there is an increasing number of more careful and inquiring men and women who take advantage of the small price at which Mr. Darwin’s wonderful book, The Origin of Species, is now to be bought, and have read that and some of his other writings, and accordingly know how far he was from being the hasty and fanciful theorist they previously imagined him to be. It is the great distinction of Darwin that he spent more than twenty years of his life in accumulating the records of an enormous series of facts and observations tending to show that the species or “kinds” of animals and plants in nature can and do change slowly, and that there is, owing to the fact that every pair produces a great number of offspring (sometimes many thousand), of which only a single pair, on the average, survive, a necessary selection of those which are to survive and breed, accompanied by a rejection and destruction of the rest. This “natural selection” or survival of favoured varieties, he was able to show, must operate like the selection made by breeders, fanciers, and horticulturists, and has in all probability (for in a history extending over hundreds of thousands of years we must necessarily deal with “probabilities,” and not with direct demonstration) produced new forms, new kinds, better adapted to their surroundings than the parental forms from which they are derived.

It was necessary, in order that Darwin should persuade other naturalists that his views were correct, that he should show by putting examples “on the table” that variations occur naturally and in great diversity; further, that there is great pressure in the conditions of life, and a consequent survival of the best-suited varieties; further, that there is in reproduction a transmission of the peculiar favouring character or quality which enables a variety to survive, and thus a tendency to perpetuate the new quality. It was not enough for Darwin to “imagine” that these things might be so, or to make the notion that they are so plausible by arguments drawn from existing knowledge. He had to do that: but also he had to make new inquiries and discover new things about animals and plants which fitted in with his theory and would not fit in either with the notion that all plants and animals were created—as the poet Milton supposed—out of lumps of earth and muddy water, suddenly, in the likeness of their present-day descendants, nor with some other notions, such as that of the able and gifted French naturalist Lamarck. And he spent the later twenty years of his life in doing so, just as he had spent the previous twenty years in collecting a first series of facts and observations justifying his theory before he announced it to the world.

A great difference between Lamarck and Darwin exists, not only in their two theories as to the mode of origin of the vast diversified series of kinds or species of plants and animals, but in their way of stating and dealing with the theory which each thought out and gave to the world. Lamarck had a great knowledge of the species of plants and animals, partly through having collected specimens himself when he was an officer in the French Republican army which was employed on the Mediterranean shores of France and Italy more than a hundred years ago, and partly through his later official position in the great natural history museum at Paris, where large collections passed through his hands. He was a man of very keen insight and excellent method, and did more to plan out a natural and satisfactory “classification” of animals than any one between his own day and that of LinnÆus. His theory of the origin of species was essentially an opposition to the then popular view that the species of living things have been made by the Creator so as to fit the conditions in which they live. Lamarck contradicted this view, and said in so many words that the real fact is that the peculiar specific characters of animals or of plants have not been created for their conditions, but, on the contrary, that the conditions in which they live have created the peculiarities of living things. In so far his conception was the same as Darwin’s. But Lamarck then said to himself: How do the conditions create the peculiarities of different living things? And he answered this question by an ingenious guess, which he published to the world in a book called Philosophical Zoology, without taking any steps to test the truth of his guess.

That is where Lamarck’s method and attitude as a scientific man is so greatly inferior to that of Darwin. Lamarck, sitting in his study, said animals (and plants too) must be affected by the conditions around them, so that an individual as it lives and grows becomes to a certain degree slightly changed by and adapted to those conditions. This, he said, we all see in human beings and familiar animals and plants. Now, he said, we have only to admit that the changes so acquired are (especially when both parents have been similarly changed) transmitted to the young in the process of generation, and to some degree “intensified,” in order to recognise that of necessity there is in nature a constant change and progression of living forms, consisting in a more and more elaborate “adaptation” to the conditions of life, which will be varied and lead to new adaptations as the living things spread over the earth or as geological changes occur. He cited the long neck of the giraffe as an example of what he meant. In regions where there was frequent and extensive drought, a deer-like creature would eat the lower leaves of trees when the grass was dried up and dead. It would strain and stretch its neck in reaching after the higher leaves, and the individuals thus straining and stretching would become an inch or two longer in the neck in consequence. These individuals would, said Lamarck, transmit their increased length of neck to their offspring, who again would strain and stretch after higher leaves, and get a further increase of neck-length, and so it would go on, little by little, over many thousand generations, until the neck-stretchers had become well marked and distinguished by their long necks from such of their ancestral stock as survived in other regions where, the grass being good, there was no inducement to straining and stretching the neck.

Now the great difference between Lamarck and Darwin is that Lamarck was quite content to state the ingenious supposition illustrated by the imaginary history of the giraffe, and to declare that this was the law of Nature and is actually going on every day, without, so to speak, getting out of his chair. He never attempted to show by observation or experiment that such a change of form as the stretching of the neck by straining after food could and did occur, or that if it did that it could be transmitted by a parent or couple of parents to their offspring. And consequently for many years no one attached much value to Lamarck’s notions on the subject. When, fifty years later, Darwin’s very different theory became widely received, based on the demonstrable fact that congenital variations (not stretchings and warpings acquired in the lifetime of a parent, but variations which are inborn, and occur in some but not other individuals living under one and the same set of conditions) are transmitted to offspring, and that those among these variations which are favourable to success in life will enable their possessor to survive and to produce young inheriting those favourable variations—then it occurred to those naturalists who were inclined to believe in Lamarck’s suggestion to inquire into the solid facts in regard to that also, and to see whether his bare statement was true. From that day to this, it has never been shown that it is true. It is, indeed, to begin with, a rare thing to find instances of either wild animals or wild plants which, growing up in unusual conditions, have their structure altered and “adapted” so as to be more serviceable in those unusual conditions than their usual structure would be; and in those cases where such adaptive alterations have been produced, every experimenter is agreed in stating that he has found that when (even after several generations in the changed conditions) the young are restored to their original conditions, they simply grow up into the original forms: no permanent change in the stock or race has been effected. Every attempt to show by experiment that a new character can be acquired by the stock in this way, and show itself by heredity alone—when the modifying adapting conditions are removed—has completely failed.

On the other hand, Darwin himself and his followers have made almost endless experiments and observations on plants and animals, establishing facts as to structure and the relation of special kinds of living things to their surroundings which can only be explained on the supposition that Darwin’s theory is true in detail; that is to say, not merely that the kinds of animals and plants have arisen from previous kinds by natural descent—that supposition is much older than either Darwin or Lamarck—but that the method by which the transformation has been brought about is (a) the occurrence in every generation of every animal and plant of minute variations in every, or nearly every, part, and (b) the continual selection in the severe struggle for existence of those individuals to grow to maturity and reproduce, which happen to present favourable variations, which variations are accordingly transmitted to the next generation, and may be intensified, so far as intensification is of value, in each succeeding generation.

A book full of observations and reflections about the structure, habits, and mode of occurrence and geography of a great number of plants and animals is Darwin’s Journal of Researches, published in 1845, and now republished as A Naturalist’s Voyage. In order to know very minutely the differences and resemblances between all the kinds or species of one group of living things Darwin studied for eight years the “cirrhipedes,” the name given to the sea-acorns and ships’ barnacles which occur in all parts of the world, some living on rocks, some on the backs of turtles, others on whales, on the feet of birds, on bits of floating wood or of pumice-stone, and some on one another! They are all hermaphrodites, but Darwin found in several a most singular thing, namely, the existence of minute males, complemental to and parasitic on the hermaphrodites. His discovery was doubted and denied, but he had the pleasure of seeing it at last fully confirmed thirty years after his book on cirrhipedes was published.

Darwin discovered that the presence of the same species of plants and of some few animals on distant mountain summits and in the Arctic region is due to the former extension of ice between these situations during the last glacial period. He was, before everything else and by necessity for the examination of his theory, a geologist, and wrote many valuable geological memoirs. The history of the origin of the species of living things consists largely in tracing them to extinct creatures, and in showing what were the possible migrations and what the conditions of land and water, temperature and vegetation, in past periods, and in regard to given areas of the globe. The book on the Fertilisation of Orchids was the first published by Darwin after the Origin of Species. In it he showed how the marvellous shapes and colours and mechanisms of the flowers of orchids are adapted to ensure cross-fertilisation by insects, and how they can be explained as originating by the natural selection of variations—if the value of cross-fertilisation is once recognised. The explanation of the reason for the existence of two kinds of primrose flowers—the short-styled and the long-styled—clearly arrived at by him as being a mechanism to secure cross-fertilisation, delighted him in 1862, and led him to discover the same sort of modification in other flowers. Then, in 1864, he published his researches on Climbing Plants, and later a book on the Movements of Plants, in which he discovered the mechanism and the wonderful variety of movements of plants, and showed their value to the plant, and consequent origin, by natural selection.

He especially loved to discover evidence that plants can do many things which had been thought to be only within the powers of the other section of living things—the animals; and finding during one summer holiday that the beautiful little sun-dew moves its red-knobbed tentacles so as to entrap minute insects, he discovered the whole history of Insectivorous Plants, and showed that there are many plants of various groups which catch insects and digest them in a sort of stomach, as an animal might do. Thus the water-holding pitchers of the pitcher-plants of tropical forests were explained as being food-catchers and digesters of great value to the nutrition of the plant, and their gradual formation by variation and natural selection rendered comprehensible.

His greatest book next to the Origin—containing an immense quantity of original notes and observations and valuable information from all kinds of breeders and fanciers—is the Variation of Animals and Plants under Domestication (1868). The facts recorded are discussed in the light of the great theory, and honest, fair-minded consideration is given to those which present difficulties as well as to those which clearly favour it. In 1871 came the Descent of Man, followed in 1872 by the Expression of the Emotions in Men and Animals—in which, again, it was shown that the facts as to the likeness between man and apes can be explained on the theory that natural selection and survival of favourable variations have been at work, and that the facts are hopelessly without meaning or explanation on any other hypothesis. His last published book was on The Formation of Vegetable Mould through the Action of Worms, in which he not only showed what an important part earthworms play in burying stones and rocks, and in fitting the ground for the growth of plants, but recorded some discoveries as to the senses of worms and as to their treatment of leaves by a digestive fluid exuded from the mouth so as to soften a leaf before swallowing it.

Every one of Darwin’s books abounds with new facts and new points of view disclosed by the application to first one thing and then another of his vivifying discovery-causing theory of natural selection. The subsidiary theory of the selection of brilliantly coloured males by females in pairing, as a cause of the brilliant colours and patterns of many birds and insects, is developed in his Descent of Man. It led him to many important discoveries and observations as to the colouring and ornamentation of animals, and when considered, together with Wallace’s and Bates’s theory of mimicry and of the warning and protective colourings of insects, goes far to explain all the specific colouring of animals and plants as due to natural selection and survival. A theory which has produced such prodigious results in the way of “explaining” all forms, colours, habits, and occurrences of living things—as has that of Charles Darwin—simply holds the field against all comers. When Lamarck’s theory has been shown to be consistent with the most elementary facts as to heredity, and further to afford a rational explanation of any group of biological facts, it will be time to consider how far it may be entertained in conjunction with Darwin’s theory—but not until then.