Variation is any difference in organisms of the same species, whereas gradualism is a microevolutionary theory.
A scientific theory is a given explanation on a phenomenon from the real world (e.g., the evolution theory).
The fossil record is a piece of evidence for the evolution theory (which is mainly based on natural selection).
In conclusion, variation is any difference in organisms of the same species, whereas gradualism is a microevolutionary theory.
Learn more about natural selection here:
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