Commerce and finance are departments of life in which mankind approaches nearer to unity than in any other. They are practical expressions of the instinct of self-preservation which is the first law of nature. They spring straight from the acquisitiveness which is a universal characteristic of human nature and indeed of animal and vegetable nature. Every living thing wants to acquire food. Adam Smith indeed restricts the trading instinct to mankind. 'The propensity', he says, 'to truck, barter, or exchange one thing for another ... is common to all men and to be found in no other race of animals, which seem to know neither this nor any other species of contracts. Two greyhounds in running down the same hare have sometimes the appearance of acting in some sort of concert. Each turns her towards his companion or endeavours to intercept her when his companion turns her towards himself. This, however, is not the effect of any contract, but of the accidental concurrence of their passions in the same object at that particular time. Nobody ever saw a dog make a fair and deliberate exchange of one bone for another with another dog.'[24] Mr Cannan, in his edition of the _Wealth of Nations_, very judiciously points out in a note on this passage that 'it is by no means clear what object there could be in exchanging one bone for another'. Probably if one rummaged the literature of dog stories one would find plenty of examples of commerce between dogs, and when they perform tricks to get food, we detect the germ of the exchange of a service for a commodity. When a bee takes honey from a flower and leaves in exchange the pollen from a flower of an opposite sex, it may be said to be at once a merchant, a carrier, and a matrimonial agent, and the brilliant colours with which flowers attract these merchants have been compared to the advertising posters of the human trader. But however the case may be in the animal and vegetable world, there can be no question that the trading instinct appears at a very early stage of human development. In boys the instinct to trade or swop articles appears long before they feel any inclination to fall in love or to give much serious thought to religion. The classical example is given by Mark Twain, who relates how Tom Sawyer exchanged one of his own teeth, which had been pulled out that morning, for a tick in the possession of Huckleberry Finn, and then 'the two boys separated, each feeling wealthier than before'. In fact, of course, they both were wealthier than before, because each had got something that he wanted more than the article with which he had parted; and this pleasant result sums up the whole genesis and basis of commerce.