ADAPTATION, a process of fitting, or modifying, a thing to other uses, and so altering its form or original purpose. In literature there may be, e.g., an adaptation of a novel for a drama, or in music an arrangement of a piece for two hands into one for four, etc. In biology, adaptation plays a prominent part as the process by which an organism or species becomes modified to suit the conditions of its life. Every change in a living organism involves adaptation; for in all cases life consists in a continuous adjustment of internal to external relations. Some adaptations are produced afresh in each generation, others are transmitted by heredity, having been probably fixed by natural selection. (See EVOLUTION, VARIATION AND SELECTION.)