Third, in many of these biological systems, the abstract structure specified as a signalling system—environmental source, sender, message, receiver, response—maps very naturally onto concrete biological mechanisms. For example, Ron Planer has recently argued that we should see gene expression as the operation of a signalling system (Planer 2014). His view is quite nuanced, for the identity of the sender, receiver, and message vary somewhat from case to case. For example, when a protein is a transcription factor, then the gene counts as a sender. He treats other gene-protein relations differently. The details of his view need not concern us here. The point is that there is machinery in the cell—genes, proteins mRNA transcripts, ribosomes and their associated tRNA—that can be plausibly mapped onto sender-receiver systems. There is nothing forced about mapping the information-processing sender-receiver structure onto the molecular machinery of the cell.