(1) The extensive adoption by Man of a flesh-diet many hundreds of thousands of years ago might be expected to have shortened his alimentary canal in comparison with that of the anthropoids; but not much evidence of it is obtainable. Topinard, giving a proportionate estimate, says that in Man it is about six times the length of the body, in the gibbon about eight times. Dr. Arthur Keith, in a private communication with which he has favoured me, says that the adult chimpanzee’s intestine is slightly longer than the adult man’s, but that the measurements are for certain reasons unsatisfactory, and that there have not been enough measurements of adult chimpanzees. We must remember that, on the one hand, the chimpanzee is not exclusively frugivorous, and that, on the other hand, it is not likely that Man has been at any time exclusively carnivorous; though the return of large populations to a vegetarian diet by means of agriculture is recent.
(2) Man has lost the restraint of seasonal marriage, common to the anthropoids with other animals, as determined by food-supply and other conditions of infantile welfare; though, according to Prof. Westermarck, traces of it may still be found in a few tribes.[13] That our domestic carnivores have also lost this wholesome restraint on passion and population points, probably, to some condition of a steadier food-supply as determining or permitting the change amongst ourselves. No growth of prudence, however, or habit of laying up stores can explain the steadier supply of food; since the lower savages have no prudence and no stores. On the whole, the change may be attributed (_a_) to an omnivorous habit being more steadily gratified than one entirely frugivorous or carnivorous; (_b_) to our ancestors having wandered in quest of game from country to country in which the seasons varied, so that the original correspondence of birth-time with favourable conditions of welfare was thrown out. There may also have been causes that kept down the normal numbers of the pack, so as to be equivalent, in scarce seasons, to more abundant food: the hunter’s life, whilst securing a richer normal diet, involved many destructive incidents. And this (by the way) was favourable to rapid selection and adaptation; though if the destruction had been great enough to counterbalance the advantages of animal food, it must have frustrated the whole experiment.