An adaptive system is any system that is capable of changing based on the input it receives. All adaptive systems contain internal mechanisms that cause the system to change. In biology, adaptive systems are used by ecosystems, populations and individual creatures. Computers have also been programed with adaptive features based on those seen in nature.
An adaptive system makes its adaptations based on the feedback it receives from its environment. In a feedback loop, some of the output generated is directed back as input into the system. This input can then be used by the system to make adaptations. Feedback loops are referred to as being positive or negative, with the positive feedback loop tending to speed up or increase an output and the negative feedback loop tending to slow down or decrease an output.
In biology, adaptive systems can occur on both large and small scales. Ecosystems can be thought of as adaptive in that they are able to change based on the feedback they receive. A classic example of this is the study of population dynamics. As the population of rabbits goes up, for instance, the population of a predatory animal, such as foxes, rises with the surplus of food. After a point, the number of predators grows too numerous for the system and declines again when there are not enough prey animals on which to feed.
Within a single biological organism there are also many adaptive systems at work. Learning and behavior modification are adaptations an organism makes to receive more positive input from the environment. Feedback to individual animals tends to increase behaviors that cause pleasure and decrease those that cause pain.
Robots can also be outfitted with adaptive systems. These systems allow a robot to observe its environment and make choices based on the information received without needing a human to direct it in every action. The Mars Rovers are an example of robots that were programed with the ability to make choices. Far from Earth and the scientists that programed them, these machines had to make choices on their own while collecting data.
Software developers have also designed computer programs to be able to adapt to user needs. Many of these programs are used by people who would be unable to use traditional programs, such as speech-to-text technology. In the physical world, adaptive systems could create any number of self-improving, self-protecting systems, such as cars that drive themselves and roads that perform their own repairs. Though the ideas for such systems are plentiful, the technology that will allow many man-made objects to behave in adaptive ways has not yet been developed.