Jordan later wrote a brief note of correction agreeing with some of Gulick 's criticisms : In a later paper Gulick says that `` Moritz Wagner , in his ` Law of the Migration of Organisms , ' was the first to insist on the importance of geographical isolation as a factor in evolution , but when he asserted that without geographical isolation natural selection could have no effect in producing new species he went beyond what could be sustained by facts '' .
As well as Darwin , the Reverend J.T. Gulick also found Wagner 's theories overstated . , but in a later paper Gulick says that `` Moritz Wagner , in his `` Law of the Migration of Organisms '' , was the first to insist on the importance of geographical isolation as a factor in evolution , but when he asserted that , without geographical isolation , natural selection could have no effect in producing new species , he went beyond what could be sustained by facts '' .