A similar definition is "the function of a component in an organism is the contribution it makes to that organism's fitness".
The term is used especially in physiology, in phrases like "the function of the kidneys is to excreteurea from the body" or "the function of the heart is to push blood around the body". It is incorrect to use the word 'purpose' instead of 'function', because the word 'purpose' impliesforethought.
↑Dusenbery, David B. (1992). Sensory ecology. New York: W.H. Freeman, p7/8. ISBN0-7167-2333-6
↑Abercrombie M. et al 1992. The Penguin dictionary of biology. London: Penguin, p219. ISBN0-14-051177-6