Whether such variations or individual differences as may arise will be accumulated through natural selection in a greater or less degree, thus causing a greater or less amount of permanent modification, will depend on many complex contingencies-on the variations being of a beneficial nature, on the freedom of intercrossing, on the slowly changing physical conditions of the country, on the immigration of new colonists, and on the nature of the other inhabitants with which the varying species come into competition.
Sor daitezkeen aldakuntza edo alde indibidualak gehiago edo gutxiago metatzea, era horretan eraldaketa iraunkor handiago edo txikiagoa eraginez, zirkunstantzia oso konplexuen mende dago: