Two continental plates collide and begin to build up a mountain range. Gradually, a species of lizards becomes separated by the mountain range. The members on one side can no longer interact with members on the other side. Due to their separation, the two populations of lizards D. will likely evolve into separate species over millions of years.
This form of speciation is called allopatric speciation that happens due to the separation of a population of species by a geographical barrier. Due to the barrier the gene flow or the intermixing of the different individuals in the population stops which affects the gene frequencies in the population leading to a gradual drift in the genetic characters.
