were there any theories based on it?
Yes, Darwin's theory.
Natural selection
In 1859, Charles Darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation.
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. what is this all about? Natural selection is the differential survival and reproduction of individuals due to differences in phenotype.
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Natural selection [SEP] Darwin's theory
In 1859, Charles Darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. He defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved". The concept was simple but powerful: individuals best adapted to their environments are more likely to survive and reproduce. As long as there is some variation between them and that variation is heritable, there will be an inevitable selection of individuals with the most advantageous variations. If the variations are heritable, then differential reproductive success leads to a progressive evolution of particular populations of a species, and populations that evolve to be sufficiently different eventually become different species.