September 5, 19 12] 



NATURE 



meeting of this Association in Edinburgh in 1871. To 

 this "meteorite" theory" the apparently fatal objec- 

 tion was raised that it would take some sixty million 

 years for a meteorite to travel from the nearest stellar 

 system to our earth, and it is inconceivable that any 

 kind of life could be maintained during such a period. 

 Even from the nearest planet 150 years would be 

 necessary, and the heating of the meteorite in passing 

 through our atmosphere and at its impact with the 

 earth would, in all probability, destroy any life which 

 might have existed within it. A cognate theory, that 

 of cosmic panspermia, assumes that life may exist 

 and may have existed indefinitely in cosmic dust in 

 the interstellar spaces (Richter, 1865; Cohn, 1872), 

 and may with this dust fall slowly to the earth without 

 undergoing the heating which is experienced by a 

 meteorite. Arrhenius,'^ who adopts this theory, states 

 that if living germs were carried through the ether 

 by luminous and other radiations the time necessary 

 for their transportation from our globe to the nearest 

 stellar system would be only nine thousand years, and 

 to Mars only twenty days ! 



But the acceptance of such theories of the arrival 

 of life on the earth does not bring us any nearer to a 

 conception of its actual mode of origin ; on the con- 

 trary, it merely serves to banish the investigation of 

 the question to some conveniently inaccessible corner 

 of the universe and leaves us in the unsatisfactory posi- 

 tion of affirming not only that we have no knowledge 

 as to the mode of origin of life — which is unfortunately 

 true — but that we never can acquire such knowledge 

 — which it is to be hoped is not true."* Knowing 

 what we know, and believing what we believe, as to 

 the part played by evolution in the development of 

 terestrial matter, we are, I think (without denying 

 the possibility of the existence of life in other parts of 

 the universe "), justified in regarding these cosmic 

 theories as inherently improbable — at least in com- 

 parison with the solution of the problem which the 

 evolutionary hypothesis offers." 



The Evolutionary Hypotliesis as applied to the Origin 

 of Life. 



I assume that the majority of my audience have at 

 least a general idea of the scope of this hypothesis, 

 the general acceptance of which has within the last 

 sixty years altered the whole aspect not only of 

 biologj', but of every other branch of natural science, 

 including astronomy, geology, physics, and chemistry.''^ 

 To those who have not this familiaritv I would recom- 

 mend the perusal of a little book by Prof. Judd entitled 

 "The Coming of Evolution," which has recently 

 appeared as one of the Cambridge manuals. I know 

 of no similar book in which the subject is as clearly 

 and succinctly treated. Although the author nowhere 



" First suggested, according to Daitre, hy de Salles-Guyon (Daslre, 

 «/.«■/., p 252). The theory received the stipport of Helmhnltz. 



15 " Worlds in the Making," transl. by H. Borns, chap, viii., p. 221, 1008. 



IS "The history of science show.s how dangerous it is to brush aside 

 mysteries— zf., unsolved problems— and to interpose the barrier placarded 

 'eternal— no thoroughfare.' "—R. Meldola, Herbert Spencer Lecture, 1910. 



1" Some authorities, such as Errera, contend, «ith much probability, tliat 

 the conditions in interstellar space are such that life, as we understand it, 

 could not possibly exist there. 



IS As Verworn points out, such theories would equally apply to the origin 

 of any otter chemical combination, whether inorganic or organic, which is 

 met with on our globe, so that they lead directly to absurd conclusions. — 

 "AlUemeine Physiologic," loii. 



'!• Av Melilola insists, this general acceptance was in the first instance 

 Largely due to the writings of Herbert Speicer: " We are now prepared for 

 evolution in every domain . . . As in the case of most gr^at generalisations, 

 thought had been moving in this direction for many years. . . . Lamarck 

 and BufTTon had suggested a definite mechanism of organic development, 

 Kant and Laplace a principle of celestial evolution, while Lyell had placed 

 geology upon an evolutionary bisis. Tne principle of continuity was 

 beginning to be recognised in physical science. ... It was Spencer who 

 brought these independent lines of 'bought to a focus, and who was the first 

 to make any systema'ic attempt to show that the law of development 

 expressed in its widest and most abstract form was universally followed' 

 throughout cosmical processes, inorganic, organic, and super-organic." — 

 Ofi. cit., p. 14. 



NO. 2236, VOL. 90] 



expresses the opinion that the actual origin of life 

 on the earth has arisen by evolutioi;;,. from non-living 

 matter, it is impossible to read either this or any 

 similar exposition in which the essential unity of the 

 evolutionary process is insisted upon without conclud- 

 ing that the origin of life must have been due to the 

 same process, this process being, without exception, 

 continuous, and admitting of no gap at any part of 

 its course. Looking, therefore, at the evolution of 

 living matter by the light which is shed upon it from 

 the study of the evolution of matter in general, we 

 are led to regard it as having been produced, not by 

 a sudden alteration, whether exerted by natural or 

 supernatural agency, but by a gradual process of 

 change from material which was lifeless, through 

 material on the borderland between inanimate and 

 animate, to material which has all the characteristics 

 to which we attach the term "life." So far from 

 expecting a sudden leap from an inorganic, or at 

 least an unorganised, into an organic and organised 

 condition, from an entirely inanimate substance to a 

 completely animate state of being, should we not 

 rather expect a gradual procession of changes from 

 inorganic to organic matter, through stages of 

 gradually increasing complexity until material which 

 can be termed living is attained? And in place of 

 looking for the production of fully formed living 

 organisms in hermetically sealed flasks, should we not 

 rather search Nature herself, under natural conditions, 

 for evidence of the existence, either in the past or in 

 the present, of transitional forms between living and 

 non-living matter? 



The difficulty, nay, the impossibility, of obtaining 

 evidence of such evolution from the past history of 

 the globe is obvious. Both the hypothetical transi- 

 tional material and the living ma"terial which was 

 originally evolved from it may, as Macallum has 

 suggested, have taken the form of diffused ultra- 

 microscopic particles of living substance -° ; and even 

 if they were not diffused but aggregated into masses, 

 these masses could have been physically nothing more 

 than colloidal watery slime which would leave no 

 impress upon any geological formation. Myriads of 

 years may have elapsed before some sort of skeleton 

 in the shape of calcareous or siliceous spicules began 

 to evolve itself, and thus enabled "life," which must 

 already have possessed a prolonged existence, to make 

 any sort of geological record. It follows that in 

 attempting to pursue the evolution of living matter 

 to its beginning in terrestrial history we can only 

 e.xpect to be confronted with a blank wall of nescience. 



The problem would appear to be hopeless of ulti- 

 mate solution if we are rigidly confined to the supposi- 

 tion that the evolution of life has only occurred once 

 in the past history of the globe. But arc we justified 

 in assuming that at one period only, and as it were 

 by a fortunate and fortuitous concomitation of sub- 

 stance and circumstance, living matter became evolved 

 out of non-living matter — life became established? Is 

 there any valid reason to conclude that at some pre- 

 vious period of its history our earth was more favour- 

 ably circumstanced for the production of life than it 

 is now?"' I have vainl)' sought for such reason, and 

 if none be forthcoming the conclusion forces itself 

 upon us that the evolution of non-living into living 

 substance has happened more than once — and we can 

 be bv no means sure that it may not be happening 

 still.' 



20 There still exist in fact forms of life which the microscope cannot show 

 us(C. A. Minchin, Presidential .Address to Quekett CIu", 191 1). and germs 

 which are capable of passing through the pores of a Chamberland filter. 



21 Chalmers Mitchell (Article "Life," "Encj'cl. Brit," eleventh editions 

 writes .is follows : " It has been suggested from time to time that condition) 

 very unlik** those now existing were necessary for the first appearance of 

 life, and must be reiiealed if living matter is to be reconstituted artificially. 

 No support for such a view can be derived from observations of the existing 

 conditions of life." 



