"The process of accomodating to change" (UNESCO – UNEP, 1983, p.5)
K. KRIPPENDORFF distinguishes two kinds of adaptation: "a) Darwinian adaptation… (through which) organisms change their internal structure when their environment makes existing forms no longer viable… e.g. ASHBY's homeostat.
"b) Singerian adaptation, after SINGER, who described how organisms, particularly man, change the nature of their environment so as to eliminate threats to, or prevent the destruction of their own internal organization" (1986, p.1)
For M. BUNGE: "The word "adaptation" is ambiguous, as it designates at least three different concepts, namely the following:
"A1. Suitability of a subsystem… to a function or high value of the subsystem for the entire organism;
"A2. Adjustement of the organism to its environment
"A3. Fertility of a biopopulation" (1979, p. 104)
The three concepts could be easily generalized to sociosystems or technosystems.
If adaptation is considered a state, then the concept is tautological: any organism demonstrates merely by its actual presence that it is adapted. On the contrary, it should not be here.
Adaptation is not possible without a device that reduces the cost of regulation, by modifying the constraints within which the system must function in such a way as to reduce the amplitude of its fluctuations.
As a process, adaptation has been described by D.T. CAMPBELL as successive "increases of fit of systems to environment" (1960, p.380), through selective retention of blind variation.
There could be more to it, since a continuous evolution of the environment takes place precisely through the permanent changes brought about by the various adapting systems within it.
N. BOTNARIUC pointed out that : "Adaptation is a population or species level process (i.e. supraindividual level) and it is different in nature from adequacy; it is the result of the historical action of natural selection" (1966, p.97).