Q:

Who first developed the idea of conservation of information in physics?

I've recently come across the idea of the "conservation of information" in the so called Black Hole Information Paradox. Yet this article claims that:

Conservation of information is a term with a short history. Biologist Peter Medawar used it in the 1980s to refer to mathematical and computational systems that are limited to producing logical consequences from a given set of axioms or starting points, and thus can create no novel information (everything in the consequences is already implicit in the starting points). His use of the term is the first that I know, though the idea he captured with it is much older. Note that he called it the "Law of Conservation of Information" (see his The Limits of Science, 1984).

A:

The two notions that you refer to in your post are not necessarily the same: The "conservation of information" that is used as a principle in theoretical physics, particular in gedankenexperiments involving black holes, is more commonly known as unitarity. Unitarity became important with the advent of quantum mechanics around 1925 and was investigated rigorously in the late 1920's to early 1930's, resulting in e.g. Stone's theorem on one-parameter unitary groups.
It seems to me that this has very little to do with the "conservation of information" that your second linked article refers to, which is indeed a relatively new concept in (evolutionary) biology, it seems.

