302 CONCLUSION 



or palaeontology are able to show to the contrary, a Devonian fauna 

 and flora in the British Islands may have been contemporaneous 

 with Silurian life in North America, and with a Carboniferous fauna 

 and flora in Africa." Nobody, now, contests these views, nor 

 believes, as was formerly the case, that any advance in the suc- 

 cessional series of living forms must have occurred simultaneously 

 in different parts of the world, and, as a consequence, that strata in 

 which similar fossils are found must have been contemporaneous 

 formations. 



But, if the old view is incorrect, and if very similar faunas may 

 be found imbedded in rocks whose formation has been separated 

 by long-drawn ages of time, the difficulties besetting the biologists, 

 in regard to time, are just as great or even greater than those, in 

 regard to space or geographical distribution, to which Darwin 

 referred in the preceding quotation. 



But the distribution of similar organisms through geological 

 strata in widely different parts of the world, and in formations 

 belonging often to widely separated geological ages, will certainly 

 be also capable of receiving a much better explanation if, instead of 

 supposing that all organic forms have developed and spread from 

 one single centre, we are prepared to recognise that there have 

 been multitudes of independent centres with wide developments in 

 and from them. It should never be forgotten that, as G. H. Lewes 

 said,' " The Unk which unites all organisms is not always the 

 common bond of heritage, but the uniformity of organic laws acting 

 under uniform conditions." And if, through all the life-evolving 

 period of the history of our globe, the progress of ' organisation ' 

 seems to have been essentially similar (so that development may 

 have many times gone along more or less similar lines) this seems 

 readily explicable by the consideration that living things, both as 

 regards their origin and their subsequent differentiation or develop- 

 ment, are the immediate products of ever-acting natural laws and 

 material properties. 



And that such an essential similarity has existed may be gathered 

 from the following authoritative statements made by Prof. Huxley 

 in the address above referred to. He said : " There are two 

 hundred known orders of plants ; of these not one is certainly 

 known to exist exclusively in the fossil state. . . . The positive 

 change in passing from the recent to the ancient animal world 

 is greater, but still singularly small. No fossil animal is so distinct 

 ' " Fortnightly Review," 1868, vol. i., p. 373. 



