On our intelligence life in the hunting-pack had just as revolutionary an influence, as already explained in the first chapter. The whole art of hunting had to be learned from its rudiments by this enterprising family. With them there was no inherited instinct or disposition, and no tradition or instruction, as there is with the true carnivores: they depended solely on observation, memory, inference. With poor olfactory sense (as usual in apes) prey must be followed and inconvenient enemies outwitted, by acquiring a knowledge of their footprints and other visible signs of neighbourhood, and by discrimination of all the noises they make. The habits and manners of prey and of enemies, their favourite lairs, feeding-grounds and watering-places, their paths through forest, marsh, thicket and high grass, must all be learnt: so must their speed, endurance, means and methods of attack and defence. The whole country within the range of the pack must be known, its resources and its difficulties; and whenever new territory was entered, new lessons in all these matters had to be learned. This must have entailed a rapid natural selection of brains. Only a rapidly developing, plastic brain could have been capable of the requisite accommodation of behaviour in such conditions: a mechanism was required by which more and more new lines of specialised reaction were related to numerous newly observed and discriminated facts. The very crudest weapons may be handled with variable dexterity; the best handling must be discovered and practised; and this had a high selective value for the hands as well as for the brain. Probably crude weapons were very early used; for some monkeys (and baboons generally) throw sticks or stones, or roll stones down upon an enemy. In Borneo, Wallace came upon a female orang who, “as soon as she saw us, began breaking off branches and the great spiny fruits [of the durian] with every appearance of rage, causing such a shower of missiles as effectually kept us from approaching too near the tree. This habit of throwing down branches has been doubted; but I have, as here narrated, observed it myself on three separate occasions.”[52] The importance of the observation consists in its proving the existence in an anthropoid of the impulse to use missiles under the occasional stress of anger; so that it might be expected rapidly to develop under the constant pressure of hunger. The use of clubs and stones induced the discrimination of the best materials for such weapons, and where they could be found; and, in process of time, brought in a rough shaping of them, the better to serve their purposes. Then came the invention of snares and pitfalls and the discovery of poisons.