EXPERIMENTAL EVIDENCE ON THE EFFECT- 

 IVENESS OF SELECTION 1 



PROFESSOR H. S. JENNINGS 

 Johns Hopkins University 



In studying the problems of evolution in the common 

 infusorian Paramecium, I found that by methodical and 

 progressive selection striking results can be reached. 



From a wild culture it is possible by progressively 

 selecting in two opposite directions to obtain finally two 

 lots, one of which is many times as large as the other, 

 and the differences between the two are permanent and 

 hereditary. By properly regulated selection a great 

 variety of permanently differentiated lots are obtainable. 



Throughout this work Galton's law of regression was 

 found to hold; that is, the progeny of extreme parents 

 inherited the peculiarities of their parents, but in a less 

 marked degree. Furthermore, the results were such 

 as to lend themselves readily to interpretation as ex- 

 emplifying Galton's law of ancestral heredity. 



Thus the effectiveness of selection was clearly demon- 

 strated. But just what sort of effectiveness does the 

 theory that selection is the dynamic factor in evolution 

 demand? It demands that selection shall so act that 

 it might finally produce progress from Amoeba nip to 

 man. It must produce, from a given condition, some- 

 thing that did not before exist in that given condition. 



Has selection so acted in this case! To answer this 

 question, we must evidently know precisely what exists 

 in the condition with which we start. We therefore next 

 work with the progeny of a single individual— forming 

 a * 1 pure line," the characteristics of which we thoroughly 

 know. 



Now we try the effects of selection on this pure line. 



29, 1909. 



136 



