September 29, 192 1] 



NATURE 



155 



from it, even if we hold it only as an act of faith, 

 for there is no alternative, and, after all, the evi- 

 dence of palaeontology is unshaken. I have 

 thought it fair to lay stress on the present state 

 of uncertainty in all that concerns the origin of 

 species. On another occasion I even ventured 

 to speak of the return of " pre-Darwinian chaos." 

 But out of this chaos doubtless light will come. 

 Last year, during a joint discussion on genetics 

 and palaeontology, I specially remember a remark 

 by Miss Saunders, our then president, that 

 Mendelism is a theory of heredity, not of evolu- 

 tion — a caution not unneeded, though, as the 

 crossing hypothesis shows, the connection between 

 the two conceptions may prove to be a very close 

 one. 



Genetics is rendering the greatest service to 

 biology generally in ensuring that organisms shall 

 be thought of as races, not as isolated individuals, 

 mere chemical and physical complexes, at the 

 mercy of the environment. The whole tendency 

 of modern work is to show that in living things 

 heredity is supreme. An organism is what it is 

 by virtue of the constitution of the germ-plasm 

 derived from its parents. Dr. Church says that 

 " the more fundamental reactions, as expressed in 

 morphological units of construction, have been 

 established as constants beyond any hope of 

 change." This statement is an important one 

 for the palaeontologist, for all our attempts to 

 trace descent rest on the assumption that, in a 

 general sense and as regards certain well-estab- 

 lished characters, "like breeds like." 



The question, What do we mean by a 

 " species " ? is far too difficult a matter to discuss 

 now. Whatever we may think of Darwin's theory, 

 his "Origin of Species" is at any rate a classic, 

 and I believe we cannot do better than continue to 

 use the word in the same sense as Darwin used 

 it — i.e. essentially in the sense of a Linnean 

 species. 



That many Linnean species are real units of a 

 definite order is generally admitted. Dr. Lotsy 

 himself dwells on their distinctness, which depends 

 on their usually not inter-crossing, and appears 

 to be shown by the fact that among animals 

 members of the same species recognise each other 

 as such and habitually breed together. Such 

 habitual breeding together under natural condi- 

 tions is perhaps the best test of a species in the 

 Linnean sense. " The units within each Linneon 

 ( = species) form an inter-crossing community." 

 (Lotsy.) He adds : " Consequently it is Nature 

 itself which groups the individuals to Linneons. " 

 These " pairing communities " have recently been 

 re-christened by Dr. Lotsy " syngameons, " a 

 good name to express this aspect of the old 

 " species." 



I do not propose in these brief remarks to 

 venture on that well-worn subject the inheritance 

 of acquired characters — i.e. of such characters as 

 are gained during the lifetime of the individual 

 by reaction to the environment. There has 

 always been a strong cross-current of opinion in 

 favour of this belief, especially, in our own time, 

 NO. 2709, VOL. 108] 



in the form of "unconscious memory," so ably 

 advocated by Samuel Butler and supported by 

 Sir Francis Darwin in his presidential address 

 to the British Association at Dublin. Professor 

 Henslow% as we all know, is a veteran champion 

 of the origin of plant structures by self-adapta- 

 tion to the environment. On the other hand, 

 some geneticists roundly deny that any inheritance 

 of somatically acquired characters can take place. 

 In any case, the evidence, as it seems, is still too 

 doubtful and inadequate to warrant any conclu- 

 sion, so, however fascinating such speculations 

 may be, I pass on. 



To bring these introductory remarks to a close, 

 we see that while the theory of descent or evolu- 

 tion is undisputed, we really know nothing certain 

 as to the way in which new forms have arisen 

 from old. During the reign of Darwinism we 

 commonly assumed that this had happened by the 

 continual selection of small variations, and we 

 are no longer in a position to make any such 

 assumption. 



We have been told on high authority that " as 

 long as we do not know how Primula obconica 

 produced its abundant new forms it is no time to 

 discuss the origin of the Mollusca or of Dicotyle- 

 dons." (Bateson.) Yet this is just the kind of 

 speculation in which a palaeontologist is apt to 

 indulge, and if kept off it he would feel that his 

 occupation was gone ! However, so long as we 

 may believe, as already said, that, on the whole, 

 like breeds like, that grapes do not spring from 

 thorns or figs from thistles, there is perhaps still 

 sufficient basis for some attempt to interpret the 

 past history of plants in terms of descent. But 

 certainly we have learnt greater caution, and we 

 must be careful not to go far beyond our facts, 

 and, in particular, to avoid elaborate derivations 

 of one type of structure from another where the 

 supposed transitional forms have but a purely 

 subjective existence; we have realised the diffi- 

 culty of tracing homologies. We may still be 

 allowed to seek affinities, even where we cannot 

 trace descent. And though we may sometimes 

 go a little beyond our tether and give rein to 

 bolder speculations, there is no harm done so long 

 as we know what we are doing, and there may be 

 even some good in such flights if our scientific 

 use of the imagination serves to give life to the 

 dry bones of bare description. On this subject 

 I am somewhat more optimistic than Dr. Lotsy, 

 who, abandoning his " Stammesgeschichte " 

 point of view, has dismissed all attempts at phylo- 

 genetic reconstruction as "fantastic." 



There are some questions of the highest interest 

 that at present can scarcely be approached in any 

 other but a speculative way. Within the last 

 vear or two new points of view have thus been 

 opened out. For example, Dr. Church's able 

 essav on " Thalassiophyta and the sub-aerial 

 transmigration " has brought vividly before us 

 the great change from marine to terrestrial life. 

 Dr. Church puts the actual conquest of the land 

 in the foreground. We watch the land slowly 

 rising toward the surface of the primeval ocean, 



