Hi!
The ancestral finch founded a new population on one of the Hawaiian Islands. Due to the founder effect , allele frequencies of the first small population on one of the islands could have differed from their continental goldfinch-like ancestors. The process of natural selection resulted in adaptation and evolution of the island population into a new species over time. Some of the birds crossed to some of the other islands where they were geographically isolated and evolved into more species occupying different niches.
In terms of population genetics, founder effect is when there is a loss of genetic diversity as a result of the establishment of a new population by a relatively few individuals. Following such an establishment, natural selection is the process which results in the genes of the fittest individuals of the population being selected over generations. This process ultimately results in evolution, and over time may give rise to new species. Geographical isolation is the physical separation of a population from another owing to geographical changes in the terrain or area. If two populations of the same species are geographically isolated, there is a great chance over time they may evolve into two different species.
Hope this helps!
