What is the variation of traits among members of the same species called?

Identify the type of natural selection shown in the below-mentioned diagrammatic representation:-

Evolution is not continuous. It is a jerky and discontinuous process. This is the punch line of:

Assertion : Natural selection is the outcome of difference in survival and reproduction among individuals that show variation in one or more traits.
Reason : Adaptive forms of a given trait tend to become more common; less adaptive ones become less common or disappear.

While creation and presence of variation is directionless,natural selection is directional as it is in the context of adaptation. Comment.

What is the phenomenon called when variation in gene frequency in a population occurs by chance rather than by natural selection?