Suggest how the two sub-species have developed from a single ancestral population.

Two populations become separated by a barrier such as sea (geographical separation). As a result populations cannot interbreed, hence gene flow between two populations is prevented. As a consequence, only a small number of species are breeding (the founder effect) leading to a limited variety of allels. Gene mutations take place; there are different environmental conditions and selection pressures leading to changes in the allele frequency. This leads to physical and physiological changes and hence allopatric (geographic) speciation.