ABSTRACT
Charles Darwin recognized two causes for evolution, namely, the transmission to the descendants of characters acquired by their ancestors during the course of their lives, and selection. He laid more stress on the latter and was the first to point out its great importance as a cause of evolution. Advantageous mutations are still rarer— that is why evolution is so slow. But they do occur. Evolution in the cases where the evidence is most complete is known to have been very gradual. Such large changes as those produced by most genes so far studied were rare in evolution. No facts definitely irreconcilable with Darwinism have been discovered in the sixty years and more that have elapsed since the formulation of Darwin's views. As an explanation of evolution Darwin's ideas still hold the field to-day, and subsequent work has necessitated less modification of them than of those of his contemporaries in physics and chemistry.
