Self-sustainability and self-sufficiency are overlapping states of being in which a person or organization needs little or no help from, or interaction with, others. Self-sufficiency entails the self being enough (to fulfill needs), and a self-sustaining entity can maintain self-sufficiency indefinitely. These states represent types of personal or collective autonomy. On a national scale, a totally self-sufficient economy that requires little or no trade with the outside world is called an autarky. Absolute purity of personal self-sufficiency or national autarky is a theoretical concept rather than a reality, but relative degrees are observable in real-world examples.
Self-sustainability is a type of sustainable living in which nothing is consumed other than what is produced by the self-sufficient individuals. Examples of attempts at self-sufficiency in North America include simple living, homesteading, off-the-grid, survivalism, DIY ethic and the back-to-the-land movement.
Practices that enable or aid self-sustainability include autonomous building, permaculture, sustainable agriculture, and renewable energy. The term is also applied to limited forms of self-sustainability, for example growing one's own food or becoming economically independent of state subsidies. The self-sustainability of an electrical installation measures its degree of grid independence and is defined as the ratio between the amount of locally produced energy that is locally consumed, either directly or after storage, and the total consumption.
A system is self-sustaining (or self-sufficient) if it can maintain itself by independent effort. The system self-sustainability is:
- the degree at which the system can sustain itself without external support
- the fraction of time in which the system is self-sustaining
Self-sustainability is considered one of the "ilities" and is closely related to sustainability and availability. In the economics literature, a system that has the quality of being self-sustaining is also referred to as an autarky.
- Let be a random variable that denotes the steady state number of external entities on which the system depends. Let be the probability that the system depends on external entities, . Then, the system self-sustainability, , is .
- Let be the expected time during which the system is self-sustaining from time 0 up to time . Then, the system self-sustainability is the steady state fraction of time in which it is self-sustaining,
Autarky exists whenever an entity can survive or continue its activities without external assistance. Autarky is not necessarily economic. For example, a military autarky would be a state that could defend itself without help from another country.
According to the Department of Labor of the state of Idaho, an employed adult shall be considered self-sufficient if the family income exceeds 200% of the Office of Management and Budget poverty income level guidelines.
In peer-to-peer swarming systems, a swarm is self-sustaining if all the blocks of its files are available among peers (excluding seeds and publishers).
Self-sustainability and survivability
Whereas self-sustainability is a quality of one’s independence, survivability applies to the future maintainability of one’s self-sustainability and indeed one’s existence. Many believe that more self-sustainability guarantees a higher degree of survivability. But just as many oppose this, arguing that it is not self-sustainability that is essential for survivability, but on the contrary specialization and thus dependence.
Consider the first two examples presented above. Among countries, commercial treats are as important as self-sustainability. An autarky is usually inefficient. Among people, social ties have been shown to be correlated to happiness and success as much as self-sustainability.