What is genetic drift ? How genetic drift provides diversity without any adaptation ?

Explanation

Genetic drift : Refer to point 9 to Gist of the Chapter..
A colour variation arises during reproduction in the population of red beetles. There is one beetle is blue in colour. This beetle can pass the colour on to its progeny, so that all its progeny beetles are blue.

Crows can see blue as well as red beetles in the green leaves of the bushes and therefore can eat them. Initially in the population, as it expands, there are a few blue beetles, but most are red. An elephant comes by and stumps on the bushes where the beetles live. This kills most of the beetles. Few blue beetles survive by chance among the red beetle population. Blue colour has no adaptive value as in case of green colour. The beetle population slowly expands again but now there are mostly blue beetles in the population.
This blue colour change gave no survival advantage, it was simply a matter of accidental survival of beetles of one colour (blue) that changed the common characteristic of the resultant population.
An accident can change the frequency of some genes in a population, even if they give no survival advantage. Genetic drift provides diversity without any adaptation.