Zenophanes (500 B.C.), as well as Leonardo da Vinci two thousand years later, caught the true explanation but popular opinion was not satisfied. They were caused by some "formative quality" or "plastic virtue" of the soil; by some "lapidific juice," or the influence of heavenly bodies. Perhaps the devil had made them in order to upset man's faith or perchance God had made them to test man's faith. As collections were made the true interpretation became unavoidable, but this raised some great difficulties especially after man knew enough to measure the relative age of the rocks in which they were formed.

It became apparent that the animals whose bones formed the fossils were very different from animals known to be alive on earth. Moreover, existing forms were not found in the fossil-bearing strata. Evidently these old types had once lived in large numbers and it was not easy to imagine what had destroyed them.

The French naturalist Baron Cuvier (1769-1832), the founder of vertebrate paleontology, seems to have been the first to gain a wide knowledge of fossil forms. He sought to explain their appearance and disappearance by assuming a series of special creations, followed by a series of cataclysms or catastrophes which destroyed them, their places being taken by immigrant forms coming from some creation center. That the fossil forms might in any way be ancestral to the latter seems not to have occurred to him. Such catastrophes may well have played a part in the local destruction of many organisms. It is hard, for instance, to imagine the survival by horses and cattle of the 1927 flood of the Mississippi River, unless they were aided by man. Nevertheless the increasing body of facts did not fit the theory of Cuvier and, after many revisions, it was abandoned. To this the growth of the idea that we can best explain the past by the present may have contributed. We find plenty of gradual changes, few catastrophes, and no sudden appearances of markedly

new forms of life. Serial creation would have to be endless to meet possible future catastrophes.

As geology developed it was discovered that there was an order in the appearance of the fossils. Now we divide the history of the rocks into ages and we find that fossils are characteristic of each as is shown in the table on page 25ff. The record begins with the lowest shell-forming types and goes on to the age of mammals. Again hard and fast lines are impossible. Birds and reptiles have certain similarities of structure which are striking. The early mammals are not like the later but there seem to be certain resemblances and the change appears to be a step at a time rather than cataclysms, though the scene shifts from one part of earth to another, for the whole story is not told in any one area.

Geographical Distribution of Life

The current distribution of life on earth had long puzzled thinking men. Since the earth was held to be a plane, evidently no animals could live on the lower side, for either they must fall off or else stand with feet above their heads. St. Paul had declared that the Gospel had gone to all lands, hence Augustine concluded that there could be no persons living in the Antipodes or other unknown and distant areas. He thought, too, that God had caused, or permitted, the angels to distribute the animals over the earth. In 1667 Milius was puzzled by the fact that many animals common on earth were not found near Mount Ararat. He could not conceive of their having wandered so far. The suggestion that they had been carried by human agency was opposed as early as 1590 by Joseph Acosta in his Natural and Moral History of the Indies. "It was sufficient, yea, very much, for men driven against their willes by tempest, in so long and unknowne a voyage, to escape with their owne lives, without busying themselves to carrie woolves and foxes, and to nourish them at sea." Even assuming that good travelers had made their

way over earth, how could such species as the sloths of South America make so great a journey from Mount Ararat? If the kangaroo, duckbill and apteryx could reach Australia, why not the carnivorous wolves and tigers of Asia?

Variation

The variation of domestic plants and animals must have been observed in early times. This seems to have caused no special concern, for even the church fathers could hold to spontaneous generation and satisfy their minds in some such fashion as did Aquinas when he wrote: "Nothing was made by God, after the six days of creation, absolutely new, but it was in some sense included in the work of the six days" and that "even new species, if any appear, have existed before in certain native properties, just as animals are produced from putrefaction." The fundamentalists of to-day might do worse than ponder the possibilities of the argument of Aquinas.

Omitting from the present discussion the brilliant speculations of the Greeks, unhampered by Biblical questions, a thousand years elapse from the time when Augustine gave his mighty approval to the authority of the Bible and the raising of a question as to the immutability of species by Francis Bacon (1561-1626). Bacon asked if the changes which had taken place might not be explained as the acmumulated effects of variations. From this time on an increasing group of men, including both scientists and philosophers, Leibnitz, Schelling, Kant, Goethe, Lessing, Descartes, among them, are questioning the older explanation.

Linnæus

THE EXPLORERS OF EVOLUTION

In the seventeenth century John Ray had started to catalogue plants and animals but the new era in natural science

really dates from the work of the Swedish botanist Linnæus (1707-1778). At first he held to the common opinion of his day but as his information grew he was forced to modify his ideas. By 1762 he admits, following the suggestion of the Benedictine Dom Calmet, that "all the species of one genus constituted at first one species; they were subsequently modified by hybrid generation; that is by intercrossing with other species." In the last edition of his great work, Systema Natura, he no longer asserted the fixity of species.

Buffon

The French student of animal life, Buffon (1707-1788), was the next naturalist to break from the old views. "The pig does not appear to have been formed upon an original, special and perfect plan, since it is a compound of other animals; it has evidently useless parts, or rather parts of which it cannot make any use, toes all the bones of which are perfectly formed, and which nevertheless, are of no service to it. Nature is far from subjecting herself to final causes in the formation of her creatures." "

In middle life he emphasized the rapid variation of species. "One is surprised at the rapidity with which species vary, and the facility with which they lose their primitive characteristics in assuming new forms." Or again: "How many species being perfected or degenerated by the great changes in land and sea, by the favors or disfavors of nature, by food, by the prolonged influences of climate, contrary or favorable, are no longer what they formerly were.”

Buffon saw the changes in domestic animals. He noted the high birth rate, the struggle for existence, and the elimination of many individuals. He hints at the common origin of the ass and horse, of man and ape. He thought that the environment modified animals and urged that present changes be studied in order that older changes might be understood. It is hard to judge Buffon. Frequently he is