Looking to geographical distribution, if we admit that there has been during the long course of ages much migration from one part of the world to another, owing to former climatical and geographical changes and to the many occasional and unknown means of dispersal, then we can understand, on the theory of descent with modification, most of the great leading facts in Distribution.
Geografi banakuntzari dagokionez, onartzen badugu, aroak joan aroak etorri, antzinako klima eta geografi aldaketen eta noizbehinkako sakabanaketa-bitarteko ezezagun askoren ondorioz, munduan alde batetik bestera migrazio handia izan dela, orduan, eraldaketadun ondorengotzaren teoriaren arabera, ulertu ahal izanen ditugu geografi banakuntzako egitate nagusirik gehienak.