as the assumption of the upright posture, the reduction in the jaw and its musculature, the reduction in the acuity of smell and hearing, demand, if the species is to survive, either a delicacy of adjustment with the compensatingly developing intelligence so minute as to be almost inconceivable, or the existence of some kind of protective enclosure, however imperfect, in which the varying individuals were sheltered from the direct influence of natural selection. The existence of such a mechanism would compensate losses of physical strength in the individual by the greatly increased strength of the larger unit, of the unit, that is to say, upon which natural selection still acts unmodified.
A realization, therefore, of this function of gregariousness relieves us from the necessity of {23} supposing that the double variations of diminishing physical and increasing mental capacity always occurred pari passu. The case for the primitiveness of the social habit would seem to be still further strengthened by a consideration of such widely aberrant developments as speech and the æsthetic activities, but a discussion of them here would involve an unnecessary indulgence of biological speculation.