Two plus two.
Sir Francis Gallon (1822-1911), English scientist, explorer, anthropometrist, has related that the primitive Damaras of Africa, in bartering two sticks of tobacco for one sheep as the rate of exchange, became hopelessly confused when a white trader, desiring two sheep, offered four sticks of tobacco at once. Fraud was suspected by the Damaras, and the transaction had to be revised and carried out more slowly. First two sticks of tobacco were given and one sheep driven away, then two more sticks of tobacco and the second sheep claimed. When shown that the result came out the same as the trader's original proposal, the tribesmen regarded the trader as one possessed of magic powers.
Yet, these Damaras were not unintelligent. They knew precisely the size of a flock of sheep or a herd of oxen, and would miss an individual at once, because they knew the faces of all of the animals. To us, this form of intelligence, which is true and keen observation, would be infinitely more difficult to cultivate than that involved in counting.