Q.Why is heritable variation essential for natural selection to act at all, and why does the appearance of a new mutation in a population not, by itself, constitute evolution?

Heritable variation is essential for natural selection to act at all, since selection works by differential survival and reproduction of individuals with different heritable traits — without variation, every individual would be equally fit, giving selection nothing to discriminate between. Mutation is the ultimate original source of new genetic variation: a sudden, heritable change in DNA sequence, arising spontaneously through replication errors or induced by mutagens, that typically first appears in just one individual and does not by itself constitute evolution until its frequency actually changes across the population. Recombination, the second major source of variation, does not create new genetic information but reshuffles already-existing alleles into new combinations, through two meiotic processes: crossing over (physica …