Answer: In modern view, the origin of variation is mutation. Since Darwin stated that variation will occurs in the most useful part and is retained, most people don't use their left hands, if according to Darwin's theory, those left hands should be going to extinct by now.
If Darwin's theory of variation is acceptable, then dwarfs who always want to be giant, by stretching the body, would have become giant by now.
Darwin just had a general idea about variation, offsprings tends to change in appearance from the parents. But this variation is not in terms of usefulness of the body parts of the parents, it is in terms of Gene mutation of the parents in their offspring.
Explanation: Darwin's 1859 theory set out a theory of Evolution by natural selection to explain adaptation and speciation.
According to Darwin's theory, individual of one generation are qualitatively different from one another this is as a result of natural selection. But in modern science, this is as a result of Gene mutation.
