We describe an approach to measuring biological information where ‘information’ is
understood in the sense found in Francis Crick’s foundational contributions to
molecular biology. Genes contain information in this sense, but so do epigenetic factors, as many biologists have recognized. The term ‘epigenetic’ is ambiguous, and we
introduce a distinction between epigenetic and exogenetic inheritance to clarify one
aspect of this ambiguity. These three heredity systems play complementary roles in
supplying information for development.
We then consider the evolutionary significance of the three inheritance systems. Whilst
the genetic inheritance system was the key innovation in the evolution of heredity, in
modern organisms the three systems each play important and complementary roles in
heredity and evolution.
Our focus in the earlier part of the paper is on ‘proximate biology’, where information
is a substantial causal factor that causes organisms to develop and causes offspring to
resemble their parents. But much philosophical work has focused on information in
‘ultimate biology’. Ultimate information is a way of talking about the evolutionary
design of the mechanisms of development and inheritance. We conclude by clarifying
the relationship between the two. Ultimate information is not a causal factor that acts
in development or heredity, but it can help to explain the evolution of proximate
information, which is.