Conversation so far:
who proposed a theory of evolution based on acquired characteristics
This idea of the inheritance of acquired characteristics or soft inheritance is inaccurately named after the French biologist Jean-Baptiste Lamarck; however, it was known from the classical era onwards.
what is lamarckism in contrast of?
The opposite of Lamarkism is Darwinism.

Question: who developed the theory?
Self-contained rewrite: who developed darwinism?