145 



A NASCENT SPECIES. 



By W. Sachse, 



From the enormous powers of increase possessed by all 

 organisms, and the consequent struggle for existence amon^ 

 them ; further, from the occurrence of gi-eat individual variation" 

 combined with the hereditary transmission of such variations' 

 necessarily arises, as Darwin termed it, " the preservation 

 of favoured races in the struggle for life." The ever-changing 

 conditions of life will either be favourable or unfavourable to 

 the existence of living beings, and it is evident that those 

 organic forms whose variations are such as to benefit them more 

 than other forms, will have a much better chance of maintaining, 

 themselves. Again, by preserving and accumulating those 

 variations they will become more and more improved, so that 

 their constant improvement must lead to their gradual advance- 

 ment in organisation, and their rapid reproduction. This again 

 must be the cause of displacing individuals, which have not 

 varied to the same extent, by step by step diminishing their 

 numbers and finally exterminating them altogether. For, takincr 

 into account the enormous destruction of life, only such 

 organisms will be able to survive as can produce their kind in 

 proportionate numbers. Thus large groups of organisms will be 

 formed as long as their modifications tend to bring them into 

 harmony with the conditions of their existence. The continuous 

 action of the struggle for existence, under the ever-changino- 

 conditions of the universe, must lead to the development of new 

 species and the extinction of some of the old. Thus the fittest 

 will survive. 



An illustrative instance of this, although only due to protec- 

 tive colouring, seems to take place at present in the case of the 

 so-called " Peppered Moth," Amphidasys bdularia, or rather of 

 Its variety Dotibledayaria. The type is of a mottled grey 

 whereas the variety is almost black, whereby it perhaps better 

 escapes its enemies. This black variety appears to be of com- 

 paratively recent origin, since it was first recorded by the late 

 Mr. Doubleday, after whom it is named. Not so very long ago 

 it used to be considered rare, and only few collectors could "boast 

 of a specimen, while now it almost appears to be more common 

 than the type. England was formerly the only country where 

 It occurred, but in recent years it has turned up on the Rhine 

 and elsewhere, and bids fair to supersede the type altogether. 



