several species, or forms of animal life, there comes about a nervous organization which acts freely within certain limits, but in a fixed and invariable mode, so that the movements are uniformly the same, and not in any proper sense volitional. To such an animal we should not attribute any mind, for mind implies some power of comparison and variation, some ability to act in more than a prescribed way. This animal, which I have just supposed to possess a very limited power of nervous action, transmits that power to its descendants; and in some of the successive generations the power remains always at the same fixed point. But the laws of natural and sexual selection are perpetually operating among those descendants. In progress of time there comes to be developed another organism, which has a wider range of nervous action; and, as this ceaseless process of modification and improvement goes on, there is developed still another nervous organization which acts with still more varied movements. As the different species of animals become evolved out of those that have gone before, the expansion of nervous organization goes on; and as each new and higher and more complex stage is gained, individuals of the species have the power to transmit it to their descendants by ordinary generation. At length, as in some of the mammalia, a nervous organization is attained, whose action exhibits manifestations of what we call mind. There appears to be a power of something like reasoning and volition, because the nervous actions are so various and so much adapted to outward circumstances. Thus, before we reach the human animal, we find nervous organizations widely separated from those of the remote progenitor species, because they can do so much more, and can do it with an apparent power of voluntary variation. At last, this process of modifications accumulating upon modifications culminates in an animal in whose nervous organization we find the freest, the most complex, and the most various power of receiving into his brain the impressions derived from the external world, and of transmitting from his brain to the different organs of his body those movements which the external circumstances of his life, or his internal efforts, cause him to strive for and to effect. This animal was the primeval man.[113]