Page:Popular Science Monthly Volume 82.djvu/421



HEN evolution became the accepted doctrine of the natural sciences, it was incumbent on the zoologists to construct a genealogy, or phylogeny, of the animal kingdom, one that would reveal the great highways of evolution and disclose the historic sequence in the rise of new kinds of animals, from the dawn of life to the present time, from the protozoon to man.

A complete genealogy of the animal kingdom, or even one as nearly complete as the biologist may reasonably hope to produce, would be of great value. It would represent the measure of our evidence that animal evolution had taken place. It would constitute the framework of the entire science of zoology, for at the root of every problem in anatomy, embryology, physiology and paleontology is the question of origin. It would be a moving historic picture of evolution, exhibiting the successive stages of the process and the creative value of the accompanying conditions.

The experimental methods of the laboratory and breeding-pen may measure the pliability of life under the momentary stress of artificial conditions, but only the phylogenetic history of large groups of animals, extending over immeasurably long periods of time, under various environments, can indicate the manner in which evolution actually did take place; whether it was slow or rapid, uniformly progressive or spasmodic, direct or tortuous; whether it drifted with the ebb and flow of circumstance, or opportunely threaded its way through an unyielding, but slowly changing, environment. And the manner in which