Objects Meet Requirements for Evolution
nVariation: there is a continuing abundance of different elements (class libraries).
nHeredity or replication: the elements have the capacity to create copies or replicas of themselves
(inheritance).
nDifferential "fitness": the number of copies of
an element that are created in a given
time varies, depending on interactions
between the features of that element and the
features of the environment in which it persists
(reuse).
Daniel Dennett.