He wrote of natural modifications occurring during reproduction and accumulating over the course of many generations, producing races and even new species, a description that anticipated in general terms the concept of natural selection.
U svojim radovima pisao je o prirodnim modifikacijama koje se javljaju tijekom reprodukcije i akumuliraju tijekom niza mnogih generacija stvarajući rase, pa čak i nove vrste, te je time anticipirao u općim terminima ideju prirodnog odabira.