554 



NATURE 



[April 29, 1922 



sciences ask us what is now currently believed about the 

 origin of species we have no cl6ar 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 properties, we have become more and more im- 

 pressed with the inapplicability of the evidence to 

 these questions of origin. There is no apparatus which 

 can be brought to bear on them which promises any 

 immediate solution. 



In the period I am thinking of, it was in the char- 

 acteristics and behaviour of animals and plants in their 

 more familiar phases, namely, the zygotic phases, that 

 attention centred. Genetical research has revealed 

 the world of gametes from which the zygotes — the 

 products of fertilisation — are constructed. What has 

 been there witnessed is of such extraordinary novelty 

 and so entirely unexpected that in the presence of the 

 new discoveries we would fain desist from speculation for 

 while. We see long courses of analysis to be travelled 

 through and for some time to come that will be a 

 sufficient occupation. The evolutionary systems of the 

 eighteenth and nineteenth centuries 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 significant 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 about 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 sanguine 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 — cannot, as regards the main thesis of 

 the Drosophila workers, be any longer maintained. 

 The arguments of Morgan and his colleagues, and 

 especially the demonstrations of Bridges, must allay all 

 scepticism as to the direct association of particular 

 chromosomes 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 discovery. I come at this 

 Christmas season to lay my respectful homage before 

 the stars that have arisen in the west. What 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 obvious 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, professed men of 

 science offered positive opinions very confidently on 

 these nebulous topics which would now scarcely pass 



NO. 2739, VOL. 109] 



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 rightful 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 palaeonto- 

 logical record. In a spirit of paradox even this has 

 been questioned. It has been asked how do you know 

 for example that there were no mammals in palaeozoic 

 times } May there not have been mammals somewhere 

 on the earth though no vestige of them has come down 

 to us ? We may feel confident there were no mammals 

 then, but are we sure .? In very ancient rocks most of 

 the great orders of animals are represented. The 

 absence of the others might by no great stress of 

 imagination be ascribed to accidental circumstances. 



Happily, however, there is one example of which we 

 can be sure. There were no Angiosperms — that is to 

 say, " higher plants " with protected seeds — in the 

 carboniferous epoch. Of that age we have abundant 

 remains of a world-wide and rich flora. The Angio- 

 sperms are cosmopolitan. By their means of dispersal 

 they must immediately have become so. Their 

 remains are very readily preserved. If they had been 

 in existence on the earth in carboniferous times they 

 must have been present with the carboniferous plants, 

 and must have been preserved with them. Hence we 

 may be sure that they did appear on the earth since 

 those times. We are not certain, using certain in the 

 strict sense, that the Angiosperms are the lineal descen- 

 dants of the carboniferous plants, but it is very much 

 easier to believe that they are than that they are not. 



Where is the difficulty ? If the Angiosperms came 

 from the carboniferous flora why may we not believe 

 the old comfortable theory in the old way ? Well so 

 we may, if by belief we mean faith, the substance, the 

 foundation of things hoped for, the evidence of things 

 not seen. In dim outline evolution is evident enough. 

 From the facts it is a conclusion which inevitably 

 follows. But that particular and essential bit of the 

 theory of evolution which is concerned with the origin 

 and nature of species remains utterly mysterious. We 

 no longer feel as we used to do, that the process of 

 variation, now contemporaneously occurring, is the 

 beginning of a work which needs merely the element of 

 time for its completion ; for even time cannot complete 

 that which has not yet begun. The conclusion in 

 which we were brought up, that species are a product 

 of a summation of variations, ignored the chief attribute 

 of species, that the product of their crosses is frequently 

 sterile in greater or less degree. Huxley very early in 

 the debate pointed out this grave defect in the evidence, 

 but before breeding researches had been made on a 

 large scale no one felt the objection to be serious. Ex- 

 tended work might be trusted to supply the deficiency. 

 It has not done so, and the significance of the negative 

 evidence can no longer be denied. 



When Darwin discussed the problem of inter-specific 

 sterility in the " Origin of Species " this aspect of the 



