January 20, 1922] 



SCIENCE 



57 



But soon, though knowledge advanced at a 

 great rate, and though whole ranges of phe- 

 nomena which had seemed capricious and dis- 

 orderly fell rapidly into a co-ordinated sys- 

 tem, less and less was heard about evolution 

 in genetical circles, and now the topic is 

 dropped. When students of other sciences ask 

 us what is now currently believed about the 

 origin of species we have no clear answer to 

 give. Faith has given place to agnosticism 

 for reasons which on such an occasion as this 

 we may profitably consider. 



Where precisely has the difficulty arisen? 

 Though the reasons for our reticence are many 

 and present themselves in various forms, they 

 are in essence one; that as we have come to 

 know more of living things and their prop- 

 erties, we have become more and more im- 

 pressed with the inapplicability of the evi- 

 dence to these questions of origin. There is 

 no apparatus which can be brought to bear 

 on them which promises any immediate solu- 

 tion. 



In the period I am thinking of it was in 

 the characteristics and behavior of animals 

 and plants in their more familiar phases, 

 namely, the Zygotic phases that attention cen- 

 tered. Genetical research has revealed the 

 world of gametes from which the zygotes — the 

 products of fertilization are constructed. 

 What has been there witnessed is of such ex- 

 traordinary novelty and so entirely unexpected 

 that in presence of the new discoveries we 

 would fain desist from speculation for a while. 

 We see long courses of analysis to be traveled 

 through and for some time to come that will 

 be a sufficient occupation. The evolutionary 

 systems of the eighteenth and nineteenth cen- 

 turies were attempts to elucidate the order 

 seen prevailing in this world of zygotes and 

 to explain it in simpler terms of cause and 

 effect: we now perceive that that order rests 

 on and is determined by another equally signi- 

 ficant and equally in need of "explanation." 

 But if we for the present drop evolutionary 

 speculation it is in no spirit of despair. What 

 has been learned abovit the gametes and their 

 natural history constitutes progress upon 

 which we shall never have to go back. The 



analysis has gone deeper than the most sangu- 

 ine could have hoped. 



We have turned still another bend in the 

 track and behind the gametes we see the 

 chromosomes. For the doubts — which I trust 

 may be pardoned in one who had never seen 

 the marvels of cytology, save as through a 

 glass darkly — can not as regards the main 

 thesis of the Drosophila workers, be any long- 

 er maintained. The arguments of Morgan and 

 his colleagues, and especially the demonstra- 

 tions of Bridges, must allay all scepticism as 

 to the direct association of particular chromo- 

 somes with particular features of the zygote. 

 The transferable characters borne by the 

 gametes have been successfully referred to the 

 visible details of nuclear configuration. 



The traces of order in variation and heredity 

 which so lately seemed paradoxical curiosities 

 have led step by step to this beautiful dis- 

 covery. I come at this Christmas Season to 

 lay my respectful homage before the stars that 

 have arisen in the west. 'V\Tiat wonder if we 

 hold our breath? When we knew nothing of 

 all this the words came freely. How easy it 

 all used to look! What glorious assumptions 

 went without rebuke. Regardless of the ob- 

 vious consideration that "modification by 

 descent" must be a chemical process, and that 

 of the principles governing that chemistry 

 science had neither hint, nor surmise, nor even 

 an empirical observation of its working, pro- 

 fessed men of science offered very confidently 

 positive opinions on these nebulous topics 

 which would now scarcely pass muster in a 

 newspaper or a sermon. It is a wholesome 

 sign of return to sense that these debates have 

 been suspended. 



Biological science has returned to its right- 

 ful place, investigation of the structure and 

 properties of the concrete and visible world. 

 We cannot see how the differentiation into 

 species came about. Variation of many kinds, 

 often considerable, we daily witness, but no 

 origin of species. Distinguishing what is 

 known from what may be believed we have 

 absolute certainty that new forms of life, new 

 orders and new species have arisen on the 

 earth. That is proved by the paleontologiea! 



