Genetic drift
is a predictable event
increases genetic differences between populations
happens when random events change the genotype of a population
happens when well-adapted organisms survive and reproduce more often than poorly-adapted organisms

Genetic drift is a predictable event alongside with natural selection, mutation, and migration. In every era of generation, organisms’ genes may be passed on to its species, to further the usable genetic trait while the not-so-used genes are trashed away.

the answer is:

carbon dioxide