It is the structural isomer. It is a type of isomerism in which particles with the same sub-atomic equation have distinctive holding designs and nuclear association, instead of stereoisomerism, in which sub-atomic bonds are dependable in a similar request and just spatial game plan contrasts.
The answer is speciation by geographic isolation. When the population of a species gets separated due to reasons such as continental drift, mountains, canyons, etc. then each separated group of population may survive and adapt to their respective environment leading to speciation. These barriers do not allow the evolving populations to interbreed initially and over time when they evolve into different species they become completely reproductively isolated.