Variability. Individual Differences. Doubtful species. Wide ranging, much diffused, and common species vary most. Species of the larger genera in any country vary more than the species of the smaller genera. Many of the species of the larger genera resemble varieties in being very closely, but unequally, related to each other, and in having restricted ranges.
CHAPTER 2. VARIATION UNDER NATURE.
From On the Origin of Species by Charles Darwin.
