In evolutionary biology, the process by which those behavioral or other characteristics of individuals that promote survival in their particular environment evolve through the action of natural selection. Also refers to the outcome of the process. A troublesome concept in evolutionary biology, it refers to the process by which the structure and function of an organism become fitted to its environment in an analogy with a lock and key. It allows the organism to survive and reproduce in its environment. There are two main criteria for some thing to be an adaptation: firstly, it has a common occurrence in a population and secondly, its communality is due to the effects of natural selection. The latter implies that an adaptation has a genetic basis as natural selection operates on genetic differences between individuals via their phenotypes. The term is also used for short-term changes in behavior (e.g., as a result of sensory adaptation), but in these cases it is perhaps more appropriate to talk about ‘adjustments’ as they do not fit the two main criteria for adaptation in the evolutionary sense. Charles Darwin (1809-1882) was acutely aware of the troublesome nature of adaptation in that, while his theory of natural selection could explain the elimination of the ‘unfit’, it had difficulties accounting for the creation of the ‘fit’. The problem still remains: how could any process involving chance (viz., the selection of random mutations) give rise to optimal adaptations? If the raw material on which natural selection operates is derived from random variation, then everything and anything is possible. Thus, a criticism of the Modern synthesis has been that it cannot predict what adaptations are likely to arise, only what has a greater probability of surviving in a given environment after change has taken place. Its lack of predictive power in this respect has led to a renewal of interest in developmental and morphological constraints and the ways they might impose themselves on the potential pathways of evolutionary transformation. In effect, it amounts to restoring a role to embryology in biological evolution as witnessed previously in the writings of Conrad Hal Waddington (1905-1975) and others, and more recently in the emerging synthesis of developmental and evolutionary biology (viz., evolutionary developmental biology).
See Baldwin effect, Biological evolution, Constraint, Convergent evolution, Developmental plasticity, Environment of evolutionary adaptedness, Embryology, Evolutionary developmental biology, Habitat (ecology), Lactose tolerance, Modern synthesis, Niche (ecology), Organism, Ossification, Tautology, Theory of natural selection