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NATURE 



[Sept 9, 1875 



These are the considerations which are held to prove that the 

 inorganic structure of the globe through all its successive stages 

 — the earth beneath our feet, with its varied surface of land and 

 sea, mountain and plain, and with its atmosphere which dis- 

 tributes heat and moisture over that surface — has been evolved 

 as the necessary result of the original aggregation of matter at 

 some extremely remote period, and of the subsequent modifica- 

 tion of that matter in condition and form under the exclusive 

 operation of invariable physical forces. 



From these investigations we carry on the inquiry to the living 

 creatures found upon the earth ; what are their relations one to 

 another, and what to the inorganic world with which they are 

 associated ? 



This inquiry first (directed to the present time, and thence 

 carried backwards as fur as possible into the past, proves that 

 there is one general system of life, vegetable and animal, which 

 is coextensive with the earth as it now is, and as it has been in 

 all the successive stages of which we obtain a knowledge by 

 geological research. The phenomena of life, as thus ascer- 

 tained, are included in the organisation of living creatures, and 

 their distribution in time and place. The common bond that 

 subsists between all vegetables and animals is testified by the 

 identity of the ultimate elements of which they are composed. 

 These elements are carbon, oxygen, hydrogen, and nitrogen, 

 with a few others in comparatively small quantities ; the whole 

 ot the materials of all living things being found among those 

 that compose the inorganic portion of the earth. 



The close relation existing between the least specialised 

 animals and plants, and between these and organic matter not 

 having life, and even with inorganic matter, is indicated by the 

 difficulty that arises in determining the aiature of the distinctions 

 between them . Among the more highly developed members of 

 the two great branches of living creatures, the well-known 

 similarities of structure observed in the various groups indicate 

 a connection between proximate forms which was long seen to 

 be akin to that derived through descent from a common ancestor 

 by ordinary generation. 



The facts- of distribution show that certain forms are associ- 

 ated in certain areas, and that as we pass from one such area to 

 another the forms of life change also. The general assemblages 

 of living creatures in neighbouring countries easily accessible to 

 one another, and having similar climates, resemble one another ; 

 and much in the same way, as the distance between areas 

 increases, or their mutual accessibility diminishes, or the condi- 

 tions of climate differ, the likeness of the forms within them 

 becomes continually less apparent. The plants and animals 

 existing at any time in any locality tend constantly to diffuse 

 themselves around that local centre, this tendency being con- 

 trolled by the conditions of climate, &c., of the surrounding 

 area, so that under certain unfavourable conditions diffusion 

 ceases. 



The possibilities of life are further seen to be everywhere 

 directly influenced by all external conditions, such as those of 

 climate, including temperature, humidity, and wind ; of the 

 length of the seasons and days and nights ; of the character of 

 the surface, whether it be land or water, and whether it be 

 covered by vegetation or otherwise ; of the nature of the soil ; 

 of the presence of other living creatures, and many more. The 

 abundance of forms of life in different areas (as distinguished 

 from number of individuals) is also found to vary greatly, and 

 to be related to the accessibility of such areas to immigration 

 from without ; to the existence, within or near the areas, of 

 localities offering considerable variations of the conditions that 

 chiefly affect life ; and to the local climate and conditions being 

 compatible with such immigration. 



For the explanation of these and other phenomena of organi- 

 sation and distribution, the only direct evidence that observation 

 can supply is that derived from the mode of propagation of 

 creatures now living ; and no other mode is known than that 

 which takes place by ordinary generation, through descent from 

 parent to offspring. 



It was left for the genius of Darwin to point out how the 

 course of nature, as it now acts in the reproduction of living crea- 

 tures, is sufficient for the interpretation of what had previously 

 been incomprehensible in these matters. He showed how 

 propagation by descent operates subject to the occurrence of 

 certain small variations in the offspring, and that the preservation 

 of some of these varieties to the exclusion of others follows as a 

 necessary consequence when the external conditions are more 

 suitable to the preserved forms than to those lost. The opera- 

 tion of these causes he called Natural Selection. Prolonged 



over a great extent of time, it supplies the long-sought key to 

 the complex system of forms either now living on the earth, or 

 the remains of which are found in the fossil state, and explains 

 the relations among them, and the manner in which their 

 distribution has taken place in time and space. 



Thus we are brought to the conclusion that the directing forces 

 which have been efficient in developing the existing forms of life 

 from those which went before them, are those same successive 

 external conditions including both the forms of land and sea, 

 and the character of the climate, which have already been 

 shown to arise from the gradual modification of the material 

 fabric of the globe as it slowly attained to its present state. 

 In each succeeding epoch, and in each separate locality, the 

 forms preserved and handed on to the future were determined by 

 the general conditions of surface at the time and place ; and the 

 aggregate of successive sets of conditions over the whole earth's 

 surface has determined the entire series of forms which have 

 existed in the past, and have survived till now. 



As we recede from the present into the past, it necessarily 

 follows, as a consequence of the ultimate failure of all evidence 

 as to the conditions of the past, that positive testimony of the 

 conformity of the facts with the principle of evolution gradually 

 diminishes, and at length ceases. In the same way positive evi- 

 dence of the continuity of action of all the physical forces of 

 nature eventually fails. But inasmuch as the evidence, so far as 

 it can be procured, supports the belief in this continuity of action, 

 and as we have no experience of the contrary being possible, the 

 only justifiable conclusion is, that the production of life must 

 have been going on as we now know it, without any intermission, 

 from the time of its first appearance on the earth. 



These considerations manifestly aftbrd no sort [of clue to the 

 origin of life. They only serve to take us back to a very rem ote 

 epoch, when the living creatures differed greatly in detail from those 

 of the present time, but had such resemblances to them as to justify 

 the conclusion that the essence of life then was the same as 

 now ; and through that epoch into an unknown anterior period, 

 during which the possibility of life, as we understand it, began, 

 and from which has emerged in a way that we cannot comprehend, 

 matter with its properties, bound together by what we call the 

 elementary physical forcts. There seems to be no foundation 

 in any observed fact for suggesting that the wonderful property 

 which we call life appertains to the combinations of elementary 

 substances in association with which it is exclusively found, other- 

 wise than as all other properties appertain to the particular 

 forms or combinations of matter with which they are associated. 

 It is no more possible to say how originated or operates the 

 tendency of some sorts of matter to take the form of vapours, or 

 fluids, or solid bodies, in all their various shapes, or for the 

 various sorts of matter to attract one another or combine, than 

 it is to explain the origin in certain forms of matter of the 

 property we call life, or the mode of its action. For the present, 

 at least, we must be content to accept such facts as the founda- 

 tion of positive knowledge, and from them to rise to the appre- 

 hension of the means by which nature has reached its present 

 state, and is advancing into an unknown future. 



These conceptions of the relations ot animal and vegetable 

 forms to the earth in its successive stages lead to views of the 

 significance of type («>. the general system of structure running 

 through various groups of organised beings) very different from 

 those under which it was held to be an indication of some occult 

 power directing the successive appearance of living creatures on 

 the earth. In the light of evolution, type is nothing more than 

 the direction given to the actual development of life by the 

 surface conditions of the earth, which have supplied the forces 

 that controlled the course of the successive generations leading 

 from the past to the present. There is no indication of any 

 adherent or pre-arranged disposition towards the development of 

 life in any particular direction. It would rather appear that the 

 actual face of nature is the result of a succession of apparently 

 trivial incidents, which by some very slight alteration of local 

 circumstances might often, it would seem, have been turned in a 

 different direction. Some otherwise unimportant difference in 

 the constitution or sequence of the substrata at any locality 

 might have determined the elevation of mountains where a 

 hollow filled by the sea was actually formed, and thereby the 

 whole of the climatal and other conditions of a large area would 

 have been changed, and an entirely different impulse given to 

 the development of life locally, which might have impressed a 

 new character on the whole face of nature. 



But further, all that we see or know to have existed upon the 

 earth has been controlled to its most minute details by the 



