Chapter V: Laws of Variation

Effects of changed conditions—Use and disuse, combined with natural selection; organs of flight and of vision—Acclimatisation—Correlated variation—Compensation and economy of growth—False correlations—Multiple, rudimentary, and lowly organised structures variable—Parts developed in an unusual manner are highly variable: specific characters more variable than generic: secondary sexual characters variable—Species of the same genus vary in an analogous manner—Reversions to long-lost characters—Summary.

I have hitherto sometimes spoken as if the variations—so common and multiform with organic beings under domestication, and in a lesser degree with those under nature—were due to chance. This, of course is a wholly incorrect expression, but it serves to acknowledge plainly our