In Graham Bell's book Selection, it's written:
To some it may be a cause of regret that the natural world cannot be understood in terms of a single set of rules and laws, but at least, so far as we know, the whole of the natural world can be understood in terms of just two general systems, and no more. This book is an account of one of these, in the context of biological systems. It is an account of the Second Science
The first system or process is Selection. What is the second?