We all know the saying "There's no such thing as a free lunch". For some of us, it may be a rather cynical way of looking at the world. After all, what about things like altruism? Magnanimity? Salvation? If there's no such thing as a free lunch, well, there really ought to be.We anthropologists approach the saying from a rather different angle. The fundamental job of anthropology, you see, is to try and identify what is universal about the human race by examining its diversity. The anthropological study of economics is built around the idea of exchange, which we regard as a social as well as an economic transaction. And one of the few universal rules that anthropologists have discovered (it's right up there with rules like the universal incest taboo â€” all societies believe it's wrong to sleep with or marry close relatives â€” or the universal practice of marriage â€” which is a social and economic union between one or more males and one or more females) is the fundamental law of reciprocity.It's the law that says, well, basically, there's no such thing as a free lunch.You see, anthropologists regard exchange â€” the exchange of gifts, of goods, of services or of people â€” as being far more than simply the exchange of objects. Exchange, for anthropologists, is a social event. Simply put, economics is a marker of relations between people.Let me explain this with a few examples.1. A man sees a pair of shoes in a shoe store, fishes into his wallet, takes out some cash, hands it to the cashier, and walks away with the shoes in his hand.2. A homeowner hires an immigrant to weed the yard. The immigrant works all day in the hot sun, but when the time comes to be paid, the homeowner is nowhere to be found.3. A woman raises her children the best way she knows how. She works overtime, she puts them through school, she makes calls on their behalf, she struggles and struggles until they make successes of themselves.In each of the cases above, the exchange has a social component. In the first one, the social exchange is cut short. The man sees the shoes, picks them out (during which time he may or may not engage with the salesperson), pays for them (during which time he may or may not engage with the cashier), and leaves. The social exchange is neutral; the players involved in it are as indifferent as they can possibly be to one another.In the second, the social exchange is one-sided, uneven. A person is hired to do a job, but is never paid for that job. The relationship between the players is one of power and powerlessness; one person gets what he or she wants without paying for it.In the third, the social exchange is long-term. On the surface, it appears that the mother is giving far more than she is getting in return. However, what she is doing by investing her time, money and effort into raising her children is creating a social exchange that will last over time. Ideally, she will get some reward in the end, whether it be something as intangible as love and gratitude, or whether it be as concrete as her children's building her a house in which to live and taking over the paying of her bills.Exchange, you see, is far more complex than it would appear.So what does all of this mean on the ground?Well, think of it this way. The law of reciprocity covers three main kinds of exchanges, and these kinds of exchanges apply to different kinds of social contexts.Balanced reciprocity, where the value of the exchange is carefully calculated and paid for as soon as it takes place, is the kind of exchange that happens generally between acquaintances, or among strangers that we consider to be more or less equal to ourselves. It's the kind of exchange that happens every day in stores, in offices, at gas stations, and the fact that we fundamentally expect it to be basically a fair process is underscored by our outrage at the practice of price gouging.Negative reciprocity is where one person gets more out of the deal than the other. Usually it signals an unequal relationship. Stealing is the kind of negative reciprocity that occurs when one person, generally the thief, considers himself or herself to be situated in an inferior position from the victim; cheating is the kind of negative reciprocity that occurs when one person considers himself or herself superior to the victim.Generalized reciprocity best describes the kinds of exchanges families carry out with one another, and it's the kind of exchange on which societies are built. The practice of sacrificing our own desires for the welfare of other people, or the practice of giving without counting the cost fall into this category. In either case, what is more important than the gift itself is the creating of social relationships.So you see, lunch is never really free. Sometimes it's a rip-off; the giver has some food to off-load, and decides it's cheaper to give it away. Sometimes it's a bribe; the giver is looking for payback. Sometimes, it's a sacrifice. But it's never something that can be accepted and left behind.In this time of need and of giving, it's well worth remembering the anthropologist's law of reciprocity. In times like these, the only moral kind of giving is the kind we call generalized reciprocity, where the gifts are given as symbols of a social connection that exists and that is important. Let's give without expecting anything concrete in return â€” not favours, not votes, not thanks. Let's give very simply because we are all Bahamians, and when one hurts, we all hurt.