On the whole then, judging from man himself (and it seems most cautious and scientific to derive our main evidence from the being that we are best acquainted with), it certainly seems to me that, though the external conditions are a very important factor in Variation, the central explanation of this phenomenon should be sought in an inner law of Growth--a law of expansion more or less common to all animate nature. Partly because, as said before, the unfolding of the creature from its own needs and inward nature is an organic process, and likely to be persistent, while its modification by external causes must be more or less fortuitous and accidental and sometimes in one direction and sometimes in another; partly also because the movement from within outwards seems to be most like the law of creation in general. Under this view the external conditions would be considered a secondary--though important cause of modification; and regarded rather as the influences that give form and detail to the great primal impulse of growth from within; while the creature's own ingenuity and good luck would occupy the ground between the two--as the means whereby the external conditions in each individual case would be turned to account to satisfy the inner needs, or the inner life would be accommodated to the external conditions. If we take the external view of Variation--which is the one most favoured by modern science--modification or race-growth appears as an unconscious or accretive process, similar to the formation of a coral reef. There is no line of growth native in the race itself, but at any moment it is supposed to have an equal tendency to vary in any direction. Surrounding conditions act selectively; and by a process of weeding out certain types survive; small successive modifications are thus accumulated; and gradually and in the lapse of ages a more pliable and differentiated creature, and more adaptable to a variety of conditions, is produced--in whom however mind is incidental, and has played but small part in the creature's evolution. This in the main is the Darwinian-evolution theory.