neous with the evolution of the higher portion of the brain, and certainly dependent on that evolution, has been an evolution of mental variability, which has still further increased the correspondence. In man this power of developing mentally in response to stimulation from the environment has grown to be so great, and is of such importance in his struggle for existence, that his survival is determined mainly by virtue of it, not by his inborn mental traits (instincts), which have therefore undergone great retrogression. It follows that nations, the individuals of which have on the average large brains, which have the cerebrum and the cerebellum much developed, differ from races the individuals of which have smaller brains, which have the cerebrum and cerebellum less developed, mainly in powers of varying, of developing mentally, by acquiring mental traits in response to appropriate stimulation; not mainly in inborn traits, such as are implied when it is said that this or that race differs inherently from this or that other, in that it possesses a greater genius for empire or colonization, or music, or art, &c. Indeed, while it is conceivable that survival of the fittest has caused the evolution of the instincts properly so called (love, fear, rage, &c.), or rather, to speak more precisely, of the nervous structures which subserve these instincts; and while it is conceivable that it has caused the evolution of the higher portions of the brain, and, as a consequence, the evolution of the' power of varying mentally in response to appropriate stimulation, of acquiring fit knowledge and ways of thinking and acting from the environment; it is not conceivable that it can have produced such inborn mental differences among races, as are meant when it is said that the Englishman is "by nature" resolute, the Frenchman vain, the Italian excitable, the German phlegmatic, the West African cruel, and so forth. For it can hardly be, that
