Civilization largely sets aside the harsh but ultimately salutary action of the great law of Natural Selection without providing an efficient substitute for preventing degeneracy. The substitute on which moralists and legislators rely—if they think on the matter at all—is the cumulative inheritance of the beneficial effects of education, training, habits, institutions, and so forth—the inheritance, in short, of acquired characters, or of the effects of use and disuse. If this substitute is but a broken reed, then the deeper thinkers who gradually teach the teachers of the people, and ultimately even influence the legislators and moralists, must found their systems of morality and their criticisms of social and political laws and institutions and customs and ideas on the basis of the Darwinian law rather than on that of Lamarck.
ual selection, which might affect the outward appearance at the cost of less obvious defects or inconveniences?
Mr. Spencer points to the decay of modern teeth as a sign or result of their being overcrowded through the diminution of the jaw by disuse. But the teeth which are the most frequently overcrowded are the lower incisors. The upper incisors are less overcrowded, being commonly pressed outwards by the lower arc of teeth fitting inside them in biting. The lower incisors are correspondingly pressed inwards and closer together. Yet the upper incisors decay--or at least are extracted--about twenty times as frequently as the closely packed lower incisors. Surely this must indicate that the cause of decay is not overcrowding.
The lateness and irregularity of the wisdom teeth are sometimes supposed to indicate their gradual disappearance through want of room in a diminishing jaw. But a note on Tasmanian skulls in the Catalogue of the College of Surgeons (p. 199) shows that this la