Environmental barrier separates the population
No gene flow between populations
Random mutation introduces new alleles into populations
Conditions on either side change
So the 2 populations have different selection pressures
Determine if allele is advantageous
Individuals with advantageous allele - better adapted
More likely to survive + reproduce
Pass on advantageous alleles to offspring
Over time, frequency of advantageous allele increases
Different allele frequency in both populations
Now 2 populations are genetically distinct, cannot interbreed to produce fertile offsprings
2 different species
