Isaac's paper very nicely summarises many key issues in the field, but for this post I want to pick up on one specific issue. He discusses the distinction between what he calls "physical symbolism" and "abstract symbolism". Abstract symbolism is what I've previously referred to as arbitrary symbolism (well, maybe, see below), and this binary distinction links to the distinction between environmental and semantic information (which I discussed here).
Here's some quotes from Isaac:
In physical symbolism, the symbol has a physical property which serves as the message. For example, a shiny, smooth metal surface can serve as a symbol of high reflectivity. Or a north pole of a magnet serves as a physical symbol of attraction to a south pole magnet. The meaning or significance of a physical symbol is derived from the physical properties of the symbol itself.
In abstract symbolism, the symbol has a meaning assigned to it which does not necessarily derive from its physical properties.So far so good. He later says:
Abstract symbolism is a hallmark of intelligence. ... The ability to associate abstract symbolic significance with a distinguishable physical pattern is a key indicator of intelligence, though not the only factor. ... When abstract relationships are a necessary part of information systems, then an intelligent agent must be involved to generate or interpret or design that system.So, where does that leave the peacock? Is the peacock's tail not an abstract (arbitrary) sign? Or is the peacock intelligent? Actually, when I wrote that about the peacock I was aware or a possible problem with my claim that "the sign is arbitrary since other birds manage with different signs meaning essentially the same thing": maybe the sign is not arbitrary to the peacock (or peahen). A peacock couldn't one day decide to woo a peahen with, say, a crest, instead of his tail. He wouldn't 'know' to do that and if he did the peahen wouldn't understand. Still, I think non-human animals can work with abstract symbols, but it needs teasing out a bit more carefully, and I'm still not sure whether that being the case means that animals display intelligence or that arbitrary signs don't need intelligence.
John Maynard Smith in his chapter (The Concept of Information in Biology, page 130) in Davies and Gregersen (Information and the Nature of Reality) says of the genetic code:
The correspondence between a particular triplet and the amino acid it codes for is arbitrary. Although decoding necessarily depends on chemistry, the decoding machinery (tRNAs, assignment enzymes) could be altered so as to alter the assignments. Indeed, mutations occur that are lethal because they alter the assignments. In this sense the code is symbolic.This is the same sense of arbitrary that I was using about the peacock's tail. (I wonder, maybe there is a difference between Isaac's 'abstract' and Maynard Smith's 'arbitrary'?)
Something to flag for discussion another day. Maynard Smith argues that there is intention in the genetic code. I didn't understand that when I first read his chapter but I think I do now. (His ideas have been digested by my subconscious and were regurgitated when I was reading Isaac's paper!) But that is for a later post.