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1. A characteristic of an ancestral species or population that serves an adaptive though different function in a descendant species or population.
2. The ability of a characteristic to assume a new biological function without evolutionary modification.
(Biology) biology the possession by a species or other group of characteristics that may favour survival in a changed environment, such as the limblike fins of crossopterygian fishes, which are preadaptation to terrestrial life
pre•ad•ap•ta•tion(ˌpri æd əpˈteɪ ʃən)
Biol. a structure or property that develops in an ancestral stock and becomes useful in a descendant in a changed environment.
pre`a•dapt′ (-əˈdæpt) v.i.