[29] _Zeitschrift für Phil. n. philos. Kritik._ Vol. 95, p. 173. 1889. VOL. II. JANUARY, 1892. NO. 2. THE MONIST. MENTAL EVOLUTION. AN OLD SPECULATION IN A NEW LIGHT. The theory of organic evolution, now generally accepted, needs to be supplemented by a theory of mental evolution. On a superficial examination of the matter the necessity for such a supplementary theory does not perhaps strike one as obvious, the mental seeming naturally to arise out of the organic and to be part of one continuous development. But closer investigation and a more rigid and exact treatment bring to light certain important and peculiar features, and disclose the necessity of some such hypothesis as it is my purpose to set forth briefly in the following pages. By organic evolution I mean the natural development, whether by “selection” alone or by this in co-operation with other natural processes, of the organisms which live upon the surface of this earth; and by mental evolution I mean the natural development of the mental faculties in at least the higher animals among these organisms. Now with regard to organic evolution there is no common and general agreement in respect of the first origin of primitive life on the earth. Some evolutionists believe that the living was somewhen, somehow, and somewhere evolved from the not-living. Others do not feel justified in holding this view, and deem it wiser to restrict their speculations as to natural genesis within the limits of the organic. So too at the other end of the developmental curve; there is no common and general agreement as to the evolution of the mental faculties or spiritual being of man. Some evolutionists believe that both in body and in mind, man is the product of natural development; others do not feel justified in holding this view, and retain unshaken the conviction that man in his spiritual essence is no part nor product of the common elements of nature. Seeing then that on either side there is want of agreement, on the one hand as to the origin of life, on the other as to the origin of man, I shall deal for the most part with that large area concerning which there is a more unanimous consensus of opinion, and in the main confine my speculations within the field of mental evolution in animals, ranging, say, from the amœba to the dog.