8 



DE. E. E. GATES— CONTEIBTJTION TO A 



ratlier incomplete and not-fully-convincing evidence for both. Tlie Lamarckian factor, 

 which has always received support from anatomists and palseontologists. has in recent 

 years experienced a distinct renaissance, particularly in the attempts of Semon, 

 Rignano, and others to eliminate its main weakness hy formulating a biological 

 mechanism by means of which the transmission of acquired modifications could 

 take place. 



To return to mutation and selection, the latter at least, and perhaps also the former, 

 requires " changed conditions " in order to produce a modificational effect. But the 

 vicissitudes of chancjino: climates and distributions cannot be sufficient to produce the 

 orderly j)hylogenies which frequently appear when we view larger groups of organisms 

 as a whole, and especially when we consider the broader outlines of the palseontological 

 record. Hence, at this point both mutation and selection appear to break down as 

 evolutionary factors. The larger simultaneous evolutionary trends exhibited in the 



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history of organisms appear to present problems which are more or less apart from, 

 mere questions of species-formation in each group. These problems, together with 

 those of the origin of phyla, have been comparatively little realized in the literature of 

 experimental evolution. On the other hand, the experimental researches of the last 

 decade have made it more plain how closely is species-origin in each group bound up 

 with the biological inter-relationships of the organisms composing that group. By such 

 means it may be possible ultimately to distinguish between factors leading to the 

 production of more or less incidental and evanescent species, and those which have been 

 more vitally concerned in the phylogeny of the group. It seems at present that 

 mutations such as occur in Oenothera Lamarckimia are chiefly incidental, rather than 

 phylogenetic in value, though the lack of perspective in the case of such recent pro- 

 ductions makes it difficult to judge of their real value. The only final way to answer 

 this question is by determining whether the mutants will survive in competition and 



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leave descendants. 



Perhaps we may sum up the present status of evolutionary investigation with the 

 statement that recent researches have resulted chiefly in revealing the inadequacy of 

 single factors, such as natural selection and mutation, to account for all evolution. 

 Both these factoids have doubtless played their part, however, together with the neo- 

 Lamarckian factor, orthogenesis, and other factors, some of which have doubtless not 

 yet been perceived. New organisms do not arise by any single method, but evolution is 

 a multifarious process, and the deeper currents of evolutionary progress are still very 

 little understood. 



The greatest advances since Darwin have been made in our experimental knowledo-e 

 of heredity and its structural basis, and in the laws of variability. The foundations 

 for the laws of inheritance laid by the experiments of Mendel, and so rajndly developed 

 and amplified by Batcson and the Mendelian school with active workers in several 

 countries, have shown at least one fundamental fact— namely, the alternative expression 

 of many characters on crossing, in a wide range of plants and animals. It remains to 



