One further point must be considered before this outline sketch of the manner of man's origin can be called complete. The psychical development of Humanity, since its earlier stages, has been largely due to the reaction of individuals upon one another in those various relations which we characterize as social. In considering the origin of Man, the origin of human society cannot be passed over. Foreshadowings of social relations occur in the animal world, not only in the line of our own vertebrate ancestry, but in certain orders of insects which stand quite remote from that line. Many of the higher mammals are gregarious, and this is especially true of that whole order of primates to which we belong. Rudimentary moral sentiments are also clearly discernible in the highest members of various mammalian orders, and in all but the lowest members of our own order. But in respect of definiteness and permanence the relations between individuals in a state of gregariousness fall far short of the relations between individuals in the rudest human society. The primordial unit of human society is the family, and it was by the establishment of definite and permanent family relationships that the step was taken which raised Man socially above the level of gregarious apehood. This great point was attained through that lengthening of the period of helpless childhood which accompanied the gradually increasing intelligence of our half - human ancestors.