within the animal demands their disappearance. What these processes are we do not know, but our frank avowal of ignorance gives us a certain confidence that we shall eventually find out.
But it is not only ideas that have changed within the last two decades; methods of study have undergone an even greater revolution. De Vries, at almost the same time he discovered mutation, rediscovered the fact that heredity was by no means so mysterious and erratic as it had been generally thought. Animals and plants, he discovered, possessed many characters which behaved in very definite ways when two varieties were crossed, and that the characters of an organism could be determined largely by the interbreeding of its ancestors. Thus arose the science of genetics, which seeks to find out the numerous factors underlying the various phenomena of heredity. And since heredity is the base of all evolution, genetics has for its ultimate aim the determination of the causes of that great process which is responsible for the existence of whatever animals and plants inhabit and have inhabited the earth. The geneticist is the most modern of evolutionists; he is not satisfied with finding out what has taken place in the past; he sets out to make evolution, or tiny portions of it, take place within his own laboratories and greenhouses.
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Today, despite the assertions of a few of its opponents, the theory of organic evolution is more thoroughly alive than it has ever been
