The Geological Background. Biology

A major difficulty that stood in the way of all theories of evolution was the apparent slowness of species change. In the memory of mankind there were no cases of one species turning into another. If such a process did take place, therefore, it must be exceedingly slow, requiring, perhaps, hundreds of thousands of years. Yet throughout medieval and early modem times, European scholars accepted the literal words of the Bible and considered the earth to be only some six thousand years old, and that left no time for an evolutionary process.

In 1785, came a change. James Hutton (1726-97), a Scottish physician who had taken up geology as a hobby, published a book called Theory of the Earth. In it, he reviewed the manner in which the action of water, wind and weather slowly changed the surface of the earth. He maintained that these actions had always proceeded in the same way and at the same rate ("the uniformitarian principle"). He then pointed out that to account for such gigantic changes as the building of mountains, the gouging out of river canyons and so on, vast ages of time were required. The earth, therefore, must be many millions of years old.

This new concept of the age of the earth was at first greeted with a most hostile reception, but it had to be admitted that it helped make sense of the fossils that were now beginning to preoccupy biologists. The word "fossil" comes from a Latin word meaning "to dig" and was originally applied to anything dug up out of the earth. However, the dug-up materials that excited most curiosity were stony objects that seemed to possess structures like those of living organisms.

It seemed quite unlikely that stones should mimic life forms by accident, so most scholars felt that they had to be once-living things that had somehow turned to stone. Many suggested they were remains of creatures destroyed by Noah's flood. If, however, the earth were as old as Hutton suggested, they might be extremely ancient remains that had very slowly replaced their ordinary substance by the stony material in the soil about them.

A new look at fossils came with William Smith (1769-1839), an English surveyor turned geologist. He surveyed routes for canals (then being built everywhere) and had the opportunity to observe excavations. He noted the manner in which rocks of different types and forms were arranged in parallel layers or "strata." He noted in addition that each stratum had its own characteristic form of fossil remains, not found in other strata. No matter how a stratum was bent and crumpled, even when it sank out of view and cropped up again miles away, it retained its characteristic fossils. Eventually, Smith was able to identify different strata by their fossil content alone.

If Hutton's views were correct, then it was reasonable to suppose that the strata lay in the order in which they were very slowly formed, and that the deeper a particular stratum lay, the older it was. If the fossils were, indeed, the remains of once-living creatures, then the order in which they lived might be determined by the order of the strata in which they were to be found.

Fossils attracted the particular attention of a French biologist, Georges Leopold Cuvier (1769-1832). Cuvier studied the anatomy of different creatures, comparing them carefully, and systematically noting all similarities and differences, thus founding comparative anatomy. These studies made it possible for Cuvier to learn the necessary-relationship of one part of a body with another so well that from the existence of some bones, he could infer the shape of others, the type of muscles that must be attached, and so on. In the end, he could reconstruct a reasonable approximation of the entire animal from a small number of parts.

It seems natural that a comparative anatomist should be interested in the classification of species. Cuvier extended Linnaeus' system by grouping the latter's classes into still larger groups. One he called "vertebrata" as Lamarck had done. Cuvier did not, however, lump the rest as invertebrates. Instead, he divided them into three groups: articulata (shelled animals with joints, such as insects and crustacea), mollusca (shelled animals without joints, such as clams and snails), and radiata (everything else).

These largest groups he called "phyla" (singular, "phylum," from a Greek word meaning "tribe"). Since Cuvier's day, the phyla have been multiplied until now some three dozen phyla of living creatures, both plant and animal, are recognized. In particular, the phylum of vertebrates has been extended to include some primitive animals without vertebral columns and it is now called "chordata."

Again because of his interest in comparative anatomy, Cuvier based his own system of classification on those characteristics which indicated relationships of structure and functioning, rather than on the superficial similarities that guided Linnaeus. Cuvier applied his system of classification primarily to animals, but in 1810, the Swiss botanist, Augustin Pyramus de Candolle (1778-1841), applied it to plants as well.

Cuvier could not help but extend his system of classification to the fossils. To his experienced eye, which could build whole organisms out of parts, fossils did not merely resemble living things; they possessed features that placed them clearly in one or another of the phyla he had established. He could even classify them among the subgroups of the particular phylum to which they be-longed. Thus, Cuvier pushed biological knowledge into the far past and established the science of paleontology, the study of ancient forms of life.

The fossils, as seen by Cuvier, seemed to represent the record of an evolution of species. The deeper and older a fossil was, the more it differed from existing life forms, and some could be placed in consecutive order in a manner that seemed to demonstrate gradual change.

Cuvier, however, was a pious man who could not accept the possibility of evolutionary changes. He adopted instead an alternative view that although the earth was indeed ancient, it underwent periodic catastrophes during which all life was wiped out. After each such catastrophe, new forms of life would appear, forms that were quite different from those that had previously existed. Modern forms of life (including man) were created after the most recent catastrophe. In this view, evolutionary processes were not needed to explain the fossils, and the biblical story, supposed to apply only to events after the last catastrophe, could be preserved.

Cuvier felt that four catastrophes were needed to explain the known distribution of fossils. However, as more and more fossils were discovered, matters grew more complicated and some of Cuvier's followers eventually postulated as many as twenty-seven catastrophes.

Such "catastrophism" was not in accord with the uniformitarianism of Hutton. In 1830, the Scottish geologist, Charles Lyell, began the publication of a three-volume book. Principle of Geology, in which he popularized Hutton's views and marshaled the evidence indicating that earth underwent only gradual and noncatastrophic changes. And, to be sure, continuing studies of fossils backed Lyell. There seemed no points at all in the records of the strata where all life was wiped out. Some forms survived each period where a catastrophe was suggested. Indeed, some forms now alive have existed virtually un- changed for many millions of years.

Catastrophism held out for a while among Cuvier's followers, particularly in France, but after Lyell's book appeared, it was clearly a dying belief. Catastrophism was the last scientific stand against the theory of evolution, and when it collapsed, some form of evolutionary concept simply had to be formulated. By the mid-nineteenth century, conditions were ripe—more than ripe—for such a development and the man to bring it about was on the scene.