Paper 65— The Overcontrol of Evolution — Page 732
The bacteria, simple vegetable organisms of a very primitive nature, are very little changed from the early dawn of life; they even exhibit a degree of retrogression in their parasitic behavior. Many of the fungi also represent a retrograde movement in evolution, being plants which have lost their chlorophyll-making ability and have become more or less parasitic. The majority of disease-causing bacteria and their auxiliary virus bodies really belong to this group of renegade parasitic fungi. During the intervening ages all of the vast kingdom of plant life has evolved from ancestors from which the bacteria have also descended.
The higher protozoan type of animal life soon appeared, and appeared suddenly. And from these far-distant times the amoeba, the typical single-celled animal organism, has come on down but little modified. He disports himself today much as he did when he was the last and greatest achievement in life evolution. This minute creature and his protozoan cousins are to the animal creation what bacteria are to the plant kingdom; they represent the survival of the first early evolutionary steps in life differentiation together with failure of subsequent development.
Before long the early single-celled animal types associated themselves in communities, first on the plan of the Volvox and presently along the lines of the Hydra and jellyfish. Still later there evolved the starfish, stone lilies, sea urchins, sea cucumbers, centipedes, insects, spiders, crustaceans, and the closely related groups of earthworms and leeches, soon followed by the mollusks—the oyster, octopus, and snail. Hundreds upon hundreds of species intervened and perished; mention is made only of those which survived the long, long struggle. Such nonprogressive specimens, together with the later appearing fish family, today represent the stationary types of early and lower animals, branches of the tree of life which failed to progress.
The stage was thus set for the appearance of the first backboned animals, the fishes. From this fish family there sprang two unique modifications, the frog and the salamander. And it was the frog which began that series of progressive differentiations in animal life that finally culminated in man himself.
The frog is one of the earliest of surviving human-race ancestors, but it also failed to progress, persisting today much as in those remote times. The frog is the only species ancestor of the early dawn races now living on the face of the earth. The human race has no surviving ancestry between the frog and the Eskimo.
The frogs gave rise to the Reptilia, a great animal family which is virtually extinct, but which, before passing out of existence, gave origin to the whole bird family and the numerous orders of mammals.
Probably the greatest single leap of all prehuman evolution was executed when the reptile became a bird. The bird types of today—eagles, ducks, pigeons, and ostriches—all descended from the enormous reptiles of long, long ago.
The kingdom of reptiles, descended from the frog family, is today represented by four surviving divisions: two nonprogressive, snakes and lizards, together with their cousins, alligators and turtles; one partially progressive, the bird family, and the fourth, the ancestors of mammals and the direct line of descent of the human species. But though long departed, the massiveness of the passing Reptilia found echo in the elephant and mastodon, while their peculiar forms were perpetuated in the leaping kangaroos.
