The Geographic barrier would have led to speciation in the finches which started from the founder effect where the finches were brought to other areas of the Galapagos. They were separated geographically so they could not mate with each other. Over time, evolution occurs through natural selection and genetic drift. This leads to the population being so different so they have reproductive barriers and can no longer interbreed. They become different species.
Finches were geographically separated. This caused a split in the population. Over time, through genetic mutations and evolution, with the addition of different environments, the finches developed different traits and characteristics. Eventually, they became so different, they could not mate with each other.
