Species emergence through geographic isolation
Allopatric speciation is considered one of the main reasons for the emergence of new species and requires a geographic isolation of at least two subpopulations. Reasons for this type of geographical separation can be, for example:
Climate change (eg desertification or sea level change)
Random drifting into isolates (e.g., islands, see Darwin's fin)
Since there is no gene flow (no possibility to exchange alleles) between the two populations, the subpopulations develop due to different selection factors, mutations and also different alleles in the gene pool. The selection factors work differently because the environmental conditions in both areas are not the same. Mutations occur by chance and therefore do not affect both populations equally. And finally, the bottleneck effect ensures an unequal distribution of alleles in the gene pool. It is conceivable that certain alleles are only present in one of the two subpopulations.
Schematic example of allopatric speciation
1. original population
2. Subsequent geographic barrier separates the population into two subpopulations. From now on there is no more gene flow. Theoretically, exchange of alleles would still be possible.
3. Random and various mutations occur in the populations
4. The mutations spread in the gene pool of the respective subpopulation. Furthermore, a different selection pressure in the respective populations additionally causes a different development.
5. The geographic barrier has been lifted. Gene flow between the two subpopulations is no longer possible (see reproductive isolation) because the populations have evolved too much. Result: One kind became two!