Approach to Evolution. Biology

Linnaeus' classification, beginning with extremely broad groups and dividing into successively narrower groups, seemed like a literal "tree of life." Looking upon the representation of such a tree, however diagrammatic, it was almost inevitable that one would wonder whether the arrangement could be entirely accidental. Might not two closely related species have developed from a common ancestor, and might not two closely related ancestors have developed from a still more ancient and primitive ancestor? In short, might not the structure designed by Linnaeus have grown over the ages somewhat as a real tree might have grown? It was over this possibility that the greatest controversy in the history of biology arose.

To Linnaeus himself, a pious man devoted to the literal word of the Bible, this possibility was anathema. He insisted that every species had been separately created and that each had been maintained by divine Providence so that no species had been allowed to become extinct. His own system of classification reflected this belief, for it was based on external appearance and made no attempt to mirror possible relationships. (It was as though one were to group donkeys, rabbits, and bats into one category because all had long ears.) To be sure, if there were no relationships among species, it didn't matter how you grouped them; all arrangements were equally artificial and one might as well choose the most convenient.

Nevertheless, Linnaeus could not stop others from suggesting or supposing some process of "evolution" (the word itself did not become popular till the mid-nineteenth century) in which one species did develop from another, and in which there were natural relationships among species that ought to be reflected in the system of classification used. (In later life, even Linnaeus himself began to weaken and to suggest that new species might arise through hybridization.)

Even the French naturalist, Georges Louis Leclerc, Comte de Buffon (1707-88), easygoing, conservative, and cautious (he had collaborated with Needham in the latter's experiment on spontaneous generation, see page 34), could not help but dare the prevailing orthodoxy by suggesting such a thing.

De Buffon wrote a forty-four volume encyclopedia on natural history, as popular in his time as ever Pliny's had been, and as heterogeneous (but far more accurate). In it, he pointed out that some creatures had parts that were useless to them ("vestiges"), like the two shriveled toes a pig possessed on the sides of its two useful hoofs. Might they not represent toes that had once been full-sized and useful but that had shriveled with time? Might not whole organisms do the same? Might not an ape be a degenerated man, or a donkey a degenerated horse?

An English physician, Erasmus Darwin (1731-1802), wrote long poems dealing with botany and zoology in which he accepted the Linnaean system. In them he also adopted the possibility of changes in species brought on by environmental effects. (However, these views would undoubtedly be forgotten today, were it not for the fact that Erasmus Darwin was the grandfather of Charles Darwin, with whom evolutionary theory reached its climax.)

The coming of the French Revolution, the year after De Buffon's death, shook Europe to its core. An era of change was introduced in which old values were shattered, never again to be restored. The easy acceptance of King and Church as ultimate authorities vanished in one nation after another and it became possible to suggest scientific theories that would have been dangerous heresies earlier. Thus, De Buffon's views of the world of life were such as to make it unnecessary to deal very extensively with evolutionary doctrine. Some decades later, however, another French naturalist, Jean Baptiste de Monet, Chevalier de Lamarck (1744-1829), found it desirable to consider evolution in considerable detail.

Lamarck grouped the first four Linnaean classes (mammals, birds, reptiles, fish) as "vertebrates," animals possessing an internal vertebral column, or backbone. The other two classes (insects and worms) Lamarck named "invertebrates." (Although this twofold classification was quickly superseded, it remains in popular use among laymen.) Lamarck recognized the classes of insects and worms to be heterogeneous grab bags. He labored over them and reduced them to better order; raising them, indeed, to the level at which they stood in Aristotle's classification and beyond. He recognized, for instance, that the eight-legged spiders could not be classified with the six-legged insects, and that lobsters could not be lumped with starfish.

Between 1815 and 1822, Lamarck finally produced a gigantic seven-volume work entitled Natural History of Invertebrates, which founded modern invertebrate zoology. This work had already caused him to think about the possibility of evolution and he had published his thinking on the subject as early as 1801 and then, in greater detail, in 1809 in a book called Zoological Philosophy. Lamarck suggested that organs grew in size of efficiency if used much during life, and degenerated if not used; and that this growth or degeneration could then be passed on to the offspring. (This is often referred to as "inheritance of acquired characteristics.")

He used the then recently discovered giraffe as an example of what he meant. A primitive antelope, fond of browsing on the leaves of trees, would stretch its neck upward with all its might to get all the leaves it could. Tongue and legs would stretch, too. All these body parts would literally grow slightly longer as a result, and this lengthening, Lamarck suggested, would be passed on to the next generation. The new generation would start with longer parts and stretch them still further. Little by little, the antelope would turn into a giraffe.

The theory did not stand up, for there was no good evidence that acquired characteristics could be inherited. In fact, all the evidence that could be gathered indicated that acquired characteristics were not inherited. Even if such characteristics could be inherited, that might do for those which could undergo a voluntary stress as in the case of a stretched neck. But what about the giraffe's blotched skin which served as protective camouflage? How did that develop from an antelope's unblotched hide? Could the ancestral giraffe conceivably have tried to become blotched?

Lamarck died poor and neglected, and his theory of evolution was shrugged off. But it had opened the flood-gates just the same. Evolution might have suffered a defeat but the mere fact that it had entered the battle-ground was significant. There would be other chances to fight later.