you make a lot of good points while i'm a little off topic here .... the fault in the Baby/Adult modeling problem under oop lies mainly with programmers who think of classes solely as Nouns. if you model behavior with classes -- a *much* more generic "Person" that contains a "Move" object -- then that Person can be parametrized differently at each stage of its lifetime. that same style of coding may happen more naturally in a prototype language but it is possible in oop.