“Natural selection and speciation leads to evolution.” Justify this statement

“Natural selection and speciation leads to evolution.” Justify this statement.

Generation of new species : When a population of a species splits into two populations,
it cannot reproduce with each other. They can be known two independent species. Then a new species is generated. See example as:

A huge population of beetles feed on bushes spread a wide mountain range. The beetle population becomes very large. Individual beetles feed mostly on a nearby bushes. In that huge population of beetles, there will be sub-populations. There male and female beetles meet for reproduction to happen so most reproduction will be within these sub¬populations.
Occasionally a migrant beetle might go from one site to another or a beetle is picked up by a crow from one site and dropped in the other site. This migrant beetle will reproduce with local population.

Over generations genetic drift will accumulate different changes in each sub-population. Also natural selection may also operate differently in different geographic locations. Together the processes of genetic drift and natural selection will result in these two isolated sub-populations of beetles becoming more and more different from each other. The members of these two groups will be incapable of reproducing with each other and two generation of beetles are being generated.

Natural Selection: It is process, according to Darwin which brings about evolution of new species of animals and plants. He recognised environment as main cause of natural selection, environment would gradually weep out organisms with unfavourable variations but preserve those with favourable variations (survival of the fittest).