Please give simple definition of geographical isolation, genetic drift and natural selection.

Natural Selection- It states that the variations are selected by nature and are preserved and passed on to the next generations. They give survival advantage.

Genetic Drift- The frequency of genes can change in a small population by chance or due to accidents. This change is called genetic drift.

Geographical Isolation- When a population of species are divided into 2 subpopulations due to occurrence of a physical barrier such as mountain or rivers which prevents the flow of genes , is called geographical isolation.