the ultimate source of new variation in nature is
Genetic variation Genetic variation is brought about, fundamentally, by mutation, which is a permanent change in the chemical structure of chromosomes. Genetic recombination also produces changes within alleles.
Competition (biology) According to the competitive exclusion principle, species less suited to compete for resources should either adapt or die out, although competitive exclusion is rarely found in natural ecosystems. According to evolutionary theory, this competition within and between species for resources is important in natural selection. However, competition may play less of a role than expansion among larger clades;[3] this is termed the 'Room to Roam' hypothesis.[2]