THE POPULAR SCIENCE MONTHLY.
Either organisms were evolved in a natural way, or they were created in a supernatural way, independently of one another, Haeckel, then, considers the evolution theory, first, as a universal cosmic idea, which assumes one causal law for all natural phenomena—the theory of descent, according to which all animals and plants are derived from simple primordial organisms; and, second, as the theory of natural selection (Darwinism in the strict sense), according to which the transformation of organisms has for its essential condition natural selection in the struggle for existence. And, by-the-way, we here find in Haeckel for the first time, if we are not mistaken, the admission that "the essence of the theory of descent is not affected, whether we postulate one or whether we postulate many common ancestral forms"(monophyletic hypothesis, polyphyletic hypothesis). It used not to be so, and whoever did not believe in the primordial mammal, the primordial amniote, the primordial fish, etc., was a lost man. In this admission we see the signs of a reaction from the monophyletic genealogies, which now fill whole volumes. Haeckel then tries to prove that Virchow is a believer in the creation theory, although he nowhere says as much openly. Virchow's expression, which Haeckel quotes, that "the scheme of organization within the species is immutable—like will beget like," is susceptible of more than one interpretation.
In the second chapter, entitled "Sure Proofs of the Theory of Descent," Haeckel rejects experiment as the highest means of proof, which Virchow requires; at the same time he asks: "What is there to be proved by experiments? What can experiment prove in this case?" But I must confess that I am not at all of his opinion. Haeckel is right in maintaining that the artificial breeding of our domestic animals, such as the horse, the pigeon, and the dog, and the culture of our garden plants and culinary vegetables sufficiently demonstrate the mutability of species; that the forms purposely developed by us differ from one another far more than wild species do; that the evidence against the evolution theory, which was intended to be deduced from hybridization, is only empty talk, without sense, because several species do produce fruitful hybrids: but that the limits of experiment are here reached we can in no wise admit. Experiments like those made by Madame von Chauvin with salamanders can be repeated, not only with the lower vertebrates but also with the invertebrata, and must surely lead to very important results. I believe I can predict that the activity of working naturalists, as soon as the present rather artificial methods of hardening and dissection of organs and of whole animals, which reign now almost exclusively, shall have exhausted themselves, will be devoted to such experiments as have for their aim to prove that transformations, such as we see in Nature, can be produced at pleasure. To make this point clear, I will mention the eyeless cave-animals and parasites. To any one, however little familiar with the history of the evolution and the relations of these animals to others, they furnish a complete demon-