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 popu- 

 lations 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 off- 

 spring. Occasionally, however, a mutant appears that pos- 

 sesses 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. Evo- 

 lution 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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