The gene as a unit of selection
Well-reasoned treatments of Darwinism for wide audiences (e.g. Sober 1984; Lloyd 1988; Brandon 1990) have recently had the benefit of Dawkins' ( 1976, 1982b) and Hull's ( 1988) concepts of replicators and interactors. The concepts are general in scope, but replicators usually mean genes, and interactors the individual organisms that transmit their genes in varying degrees to future generations. Organisms do the reproducing; genes direct development and provide the heritability on which response to selection depends.
I believe these discussions to be a great improvement over many that went before but that the replicator-interactor distinction is often used in ways that subvert much of its potential usefulness. As a remedy I suggest that these terms should refer to two mutually exclusive domains of selection, one that deals with material entities and another that deals with information and might be termed the codical domain. A unit of selection in the codical domain would be a codex (codices is the only plural in my dictionary).
The material and the codical are separate domains because of a dearth of shared descriptors. In discussing the codical domain we use such terms as bits, redundancy, fidelity, and meaning. The material domain is described by color, charge, density, volume, etc. The only descriptor they have in common is time, and events in one domain can be established as before, after, or simultaneous with events in the other. A catastrophic act of arson in the seventh century was a physical event at exactly the same time as the destruction of information in the library at Alexandria. Information can exist only as a material pattern, but the same information can be recorded by a variety of patterns in many different kinds of material. A message is always coded in some medium, but the medium is really not the message.
The usefulness of maintaining a conceptual separation of these domains is clearest for cultural evolution. A century ago people followed the