Passing over to particulars, it is pertinent to enquire wherein this specific superiority consisted. In what respect was the erect ground-walking human prototype better fitted for advancement than his stoop-shouldered arboreal ancestors? Favorable structural and environmental variations are, generally speaking, along two lines: those that enable animals to escape more easily from their enemies, and those that place them in a better position to acquire sustenance for themselves. It is impossible to conceive that the pliocene precursor gained any advantage over his ape-like ancestors in the former direction by adopting an upright attitude and abandoning his arboreal abode; for in so doing he lost his earlier and easier means of escape through the trees, without acquiring by way of compensation any corresponding facility for taking flight on foot. The only alternative is, therefore, to suppose that the superiority of the human species was in connection with the food-quest. As far as quantity was concerned there was nothing, however, to be gained by coming down from the boughs, for the trees of the tertiary forest afforded a supply of nuts and fruits far in excess of the demand. The advantage must, therefore, have been qualitative, that is to say, in the way of a wider food-choice. As an erect, surface-dwelling creature man was evidently able to secure a greater variety of subsistence than his ape-like ancestors obtained from the trees. Being arboreal their food was confined to nuts and fruits, while by becoming terrestrial he was in a position to add roots and berries, and, in the course of time, also fish and flesh to his fare. Human progress appears, accordingly, to have been away from a strictly frugivorous in the direction of an omnivorous diet. A similar tendency is observable among the other anthropoids. The arboreal apes, for instance, are naturally frugivorous, but when taken from the trees and bred in captivity they readily become omnivorous. The semi-terrestrial types exhibit the same proclivities in their wild state. The gorilla, for example, usually lives on fruits, but also eats birds and their eggs, small mammals, reptiles and the like, and has even been observed to devour large animals when found dead. What is only an incipient tendency among the apes probably became an habitual practice with the ancestor of man. The superiority of the human being may thus be said to have consisted in the acquisition of qualities and the occupation of an environment which enabled him to widen the range of his food-choice.
It is evident enough that the variation of environment was favorable in this respect, for the terrestrial habitat certainly offered boundless opportunities for the development of an omnivorous taste; but it is not so easy to see how the characters we have described as human rendered these opportunities available. Berries and roots were plenty in the woods, the streams were alive with fish, and the tertiary forest
