Whether the evolution of the human mind from the animal was by insensible gradations, or by a few sudden leaps, who knows? The animal brain began to increase in size in Tertiary times, and seems to have done so suddenly, but the geologic ages were so long that a change in one hundred thousand years would seem sudden. "The brains of some species increase one hundred per cent." The mammal brain greatly outstripped the reptile brain. Was Nature getting ready for man? The air...