where does all the natural variation necessary for natural selection come from
This occurs partly because random mutations arise in the genome of an individual organism, and their offspring can inherit such mutations.
Natural selection
 This occurs partly because random mutations arise in the genome of an individual organism, and their offspring can inherit such mutations.
wiki:25631411
Natural selection [SEP] Introduction
Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Charles Darwin popularised the term "natural selection", contrasting it with artificial selection, which in his view is intentional, whereas natural selection is not. Variation exists within all populations of organisms. This occurs partly because random mutations arise in the genome of an individual organism, and their offspring can inherit such mutations. Throughout the lives of the individuals, their genomes interact with their environments to cause variations in traits.