An economy with a low level of technological knowledge and a preoccupation with the daily and, at most, seasonal food supply because techniques for long term preservation of food are generally inadequate. Work teams are small and usually only include members of the local community. Large-scale collaboration on subsistence jobs is of short duration if it occurs at all because most tasks are relatively simple and require only a few people. Work related interactions between people are of a face-to-face personal kind. People who work together hunting, gathering, herding, or tending crops are usually kinsmen or lifelong friends and neighbors. Little or no attempt is made to calculate the contribution of individuals or to calculate individual shares. Social pressure generally obligates individuals to freely share food and other products of their labour with whomever needs it or asks for it in the community. This operates as an economic levelling mechanism. As a result, there is little or no possibility of saving and becoming more wealthy than anyone else. Subsequently, the incentive to work is not only derived from a desire to acquire what is being produced. There also is the pleasure of working with friends and relatives. In addition there is potential for increased social prestige from doing the job well. Impersonal commercial exchanges rarely occur in non-market economies. They usually take the form of either barter or gifts. Every household usually provides for its daily needs from its own production. Non-market economies can only function successfully in isolation. They have always been destroyed by prolonged contact with societies that have market economies.