CUMULATIVE EVIDENCE FOR EVOLUTION
reptilian ancestors? Is it even remotely probable that the story of evolution told independently by all these natural records is false? Nature does not lie. Here, as elsewhere, several of nature’s witnesses tell the same consistent, straight story, presenting cumulative evidence that cannot be refuted.
Biology furnishes many examples of the convergence of evidence upon a common conclusion. Only a sample or two have been offered to illustrate the fact that the proof of evolution, though somewhat indirect, is conclusive. It is the sheer mass of converging and cumulative evidence that in the end wins the day for evolution.
Though most of the evidences may be called indirect, this word cannot be applied to the evidence derived from genetics in the study of evolution going on to-day. The modern geneticist breeds under observation and control huge populations of rapidly breeding animals and plants. Under his very eyes there come into being scores and hundreds of new or changed types of individuals that pass their peculiarities on to their progeny according to definite laws of inheritance. Most of the changed types (mutants) are inferior in various ways to the typical individuals of the species. Some mutants are so weak or defective that they die young and leave no offspring. Occasionally, however, a mutant appears that possesses a new character or set of characters that constitutes an improvement. Such a new character persists and becomes incorporated in the hereditary complex of the species. Evolution can thus be seen to proceed by the production of large and small hereditary variations and the persistence through heredity of the good or relatively harmless mutations.
If a species becomes geographically separated into two groups, these groups tend gradually to diverge more and more. There are at least two reasons for this divergence: first, a group of individuals that becomes isolated from the
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