They are called abrasion.
The correct answer is speciation.
Speciation is the term that describes the evolutionary process causing populations to evolve into different species. There are four different types of speciation: allopatric, peripatric, parapatric and sympatric. In this case, the process described is an allopatric speciation, the most common of these four types. Allopatric speciation happens when populations are geographically separated, an event that obstructs the gene flow. Since the gene flow stops, the populations evolve in response to the different environments that they live in.
Bones of snakes are very loosely fused together like in humans. Hence these bones can move individually allowing the snakes to be really flexible. The ribs of snakes do not join like those of humans but instead, have free ends and do not have a sternum.
They are formed into polymers.
