182 M. Bronn on the Laws of Evolution of the Organic World 



representing these facts as flowing from a positive law — as result- 

 ing from a common cause. Even then we pointed out the passage 

 of species from one bed to another, the variability of the dura- 

 tion of their existence, and the increase in the number of species, 

 genera, orders, and classes in recent periods, — circumstances 

 which support the idea of the existence of a hotter and more uni- 

 form climate in the ancient periods. Even then we indicated the 

 progressive advance to perfection of the different subkingdoms by 

 the successive appearance of more perfect groups and the extinc- 

 tion of other groups of inferior organization, and the influence of 

 the external conditions of existence upon the successive appear- 

 ance of the various types of animals and vegetables upon the 

 surface of the earth, — understanding by these external conditions, 

 atmospheric conditions and those of configuration of soil or the 

 action of other organized beings. Before 1848, these different 

 points of view had never been carefully studied in detail ; and 

 those which, like the gradual development of creation from more 

 simple to more complex organization, had been the object of 

 special investigations on the part of other authors, appeared to 

 lead to results agreeing but little with older knowledge. The 

 conclusions at which we arrived in the 'Index Palseontologicus' 

 remain true now as then. Recent researches confirm them in 

 all points. 



Nevertheless the present work is rich in new results. It 

 places the law of adaptation of the successive faunas and floras 

 to the external conditions of existence, as a fundamental law 

 which governs all the others. Considered on its negative side, 

 this law is absolute, and excludes every phenomenon which would 

 contradict it ; but considered on its positive side, it allows free 

 play to other laws subordinated to or independent of it. This 

 work shows us the necessity of the simultaneous appearance of 

 plants and animals, and teaches us that all the phenomena 

 resulting from this fundamental law flow from it in a necessary 

 and direct manner. It consequently confirms, by palseontological 

 proofs, the geological theory in favour at the present day. By 

 positive and incontestable facts, it overthrows the old idea of 

 distinct faunas and floras confined within perfectly limited strata, 

 determined by lithological limits remaining the same over all 

 the surface of the globe. It demonstrates the inequality of 

 duration of species coexisting in the same stratum. It presents 

 the law of tcrripetal evolution as an expression of the gradual 

 transformation of the surface of the globe and of its influence 

 upon the totality of the successive characters of the floras and 

 faunas. It establishes the second fundamental law, namely, 

 that of progressive development (advancing in concert with the 

 progression which might result simply from the terripetal law). 



