An isolated population is more likely to undergo
            allopatric speciation. The isolated group may be under different environmental pressures
            than its parent population, and over time an isolated group will be subject to random
            mutations which will create unique attributes.
If the
            isolated population is small in numbers, then it is subject to additional pressures. The
            first of these is the founder effect. If the frequency of any allele is different
            between the isolated group and the parent population at the time the isolation occurs,
            then the isolated group experiences genetic changes from a different starting point than
            the parent population, and is likely to follow a different path over time, resulting in
            different allele frequencies.
Very small populations are
            also prone to the bottleneck effect, which results in a loss of genetic diversity. Small
            populations are also prone to inbreeding, which again may reduce the diversity of
            alleles.
