Variations are essential for natural selection to occur. It exists in almost all populations. It is caused by mutations and erotic reproduction. Hence, all of the choices are correct.
What do you mean by Mutation?
A Mutation may be defined as the sudden, stable, and inheritable changes in the genetic material of an organism.
Variations provide the favorable traits that induce natural selection. Variations are caused by mutations, gene flow, and erotic reproduction. It exists in all life forms present on the earth.
Sometimes, variations decide the relative fitness of an organism and thus natural selection occurred.
Therefore, the correct option for this question is D.
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