...evolution of new forms of species by the modification of the old. " Natural selection," says Darwin, " acts only by the preservation and accumulation of...modifications, each profitable to the preserved being ; and as modern geology has almost banished such views as the excavation of a great valley by a single...

...never ending. Again, the theory is that these variations are produced in the struggle for existence, by the preservation and accumulation of small inherited...modifications, each profitable to the preserved being. If so, we are warranted in expecting that these preserved varieties must be in the first place actually...