This is probably the best book for general readers on the evolution of the mind currently available. Contrary to Steven Pinker's "The Language Instinct," you won't find any talk of "mentalese" or innate grammar here- as Deacon points out, saying that grammar is innate doesn't solve any problems, it just sort of pushes the problems to the side. Deacon focuses on the learning strategies (specifically, the ability to learn symbolic reference), as the basis for the evolution of language and the human brain.
Deacon does not believe that language emerges from a human-only increase in "general intelligence," which is sort of the folk psychology idea for the emergence of language- our bigger brains just made us "smarter," in some ill-defined way. The idea that intelligence and langauge are separate entities is made clear by Williams' syndrome, a clinical condition where the patient has a normal use of grammar and a superior vocabulary, but is severely retarded on most intelligence tests.
Anyone who takes Linguistics 101 (or tries to learn a second language) in college is amazed by the complexity of language. It amazes a lot of people that children are able to learn something so complicated so easily, but adults (who are more intelligent, also in an ill-defined sense) find it very hard to pick up a second language. Even animals and computer algorithms, who are better than children at learning complicated sequences of actions in order to gain a reward, cannot pick up language. Deacon explains this remarkable fact by presenting his ideas for how one learns symbolic reference, a kind of learning strategy different from any other in evolution, a learning strategy that sets humans apart. To tell you anymore then that would ruin the book, you'll have to pick it up for yourself.
Deacon's greatest gift is explaining brain evolution from the bottom level (changes in genes) and from the top level (environmental changes) with equal clarity. In doing so, he bucks both evolutionary psychologists who downplay environmental factors, as well as standard social scientists and laymen who do not understand the Darwinian evolution of the brain. The result is a natural explanation of the evolution of language.
As many others have pointed out, this book is a first step. A more technical book devoted to understanding the ability to learn symbolic references based on Deacon/Peirce's ideas would be really great. Maybe I'll sit down and write it myself.
Keep 'em coming, Terry!