As a rule, the organization of physical wholes, such as atoms, molecules, or crystals, results from the union of pre-existing elements. In contrast, the organization of biological wholes is built up by differentiation of an original whole which segregates into parts. An example is determination in embryonic development, when the germ passes from a state of equipotentiality to a state where it behaves like a mosaic or sum of regions which develop independently into definite organs.
