Evolution 327 



Darwin's Theory. — Darwin's The Origin of Species brought evo- 

 lution to the attention of the public. In it his carefully documented 

 proofs established evolution as an explanation of the observable variety 

 of living materials. As a result of his long voyage in which he saw 

 so many plants and animals, and as a result of his extensive reading 

 of Lyell's Geology and Malthus's Essay on Populations, he developed 

 his theory of the origin of species. 



Darwin's essential ideas were that in all animals both "complex 

 organs and instincts" varied in their degree of perfection. Since all 

 animals reproduce in excess to the ability of the environment to sup- 

 port them, the vast majority of individuals will not live to reproduce. 

 Due to this "struggle for existence," those individuals with the most 

 favored variations will survive. Thus by natural selection, new species 

 gradually come into being. If the environment changes, migration 

 occurs, or new favorable variations develop and other species are 

 formed. 



While there is a great deal of truth to Darwin's analysis, there are 

 certain facts which are difficult to reconcile to his views. Many varia- 

 tions seem to have little survival value and yet are passed onto succeed- 

 ing generations. Also many studies have shown that certain characters 

 change by "jumps" rather than gradually. Despite these objections, it 

 is undoubtedly true that the struggle for existence does play an im- 

 portant role in species formation. It may well be that many variations 

 which seem of no value actually are when studied from different points 

 of view. "Survival of the Fittest" as this theory has been termed 

 must occupy an important place in evolutionary thinking. 



While Darwin saw and recognized the importance of variations 

 he was at a loss to account for their manner of occurrence and further 

 for their mode of transmission to offspring. Though at this same time, 

 Mendel was cultivating his peas and providing the basis for later under- 

 standing of Darwin's variations, Darwin himself knew nothing of this 

 important work. Following Lamarck and his grandfather Erasmus, 

 Darwin emphasized the importance of acquired characteristics. He be- 

 lieved that use and disuse furnished the basis of many variations. Then 

 he reasoned that these caused the body to produce substances which 

 he termed "pangenes." These were carried by the blood and influenced 

 the germ plasm which then affected the offspring. While considering 

 the importance of acquired characters, Darwin also decided that many 

 variations must be spontaneous. Ingenious as was his theory of the 



