In the history of biology, Lamarkians were the humanists who believed that experience could enrich the genetic structure of organisms. When Weissmann proved the continuity of the germ line, which implies that phenotypic learning could not be incorporated in the genes of an organism's offspring, it led to panic for the Lamarkians. James Mark Baldwin, the developmental biologist, Lloyd Morgan and Conrad Waddington all jumped to fill the breach with a variety of mechanisms that would allow some causal arrow from learning to genes to survive the "continuity of the germ line."
Of course, phenotypes, not genotypes, are selected, so there is ample room for plastic phenotypes to be selected, and the genetic basis of their plasticity or ease of learning to adapt to particular environments to become fixed in the gene pool. However, until Dawkins' "extended phenotype" and more recently Odling-Smee, Laland, and Feldman's "niche construction" theories were developed, the whole matter was quite vague.
This conference volume outlines the history of the Baldwin Effect, and the effect of the interchange of expert opinion on the reader should be pretty clear: niche construction and in the case of humans, gene-culture coevolution are the intellectual heirs of the Baldwin Effect and are extremely important biological phenomena. Paul Griffiths' and Terrence Deacon's contributions to the volume make this crystal clear. Numerous evo-devo types also want to claim a piece of the Baldwin effect, but despite reams of material on how development affects the gene pool, I remain unconvinced. But, perhaps that's my limited perspective. At any rate, if you know a fair amount of evolutionary and developmental biology, this is really quite a fine book to read. Perhaps even better than attending the original conference.
Godfrey-Smith. The Baldwin effect purports that acquired traits can become genetically assimilated. This is supposedly because learning is fallible and expensive in terms of time and cognitive resources, so a hard-wiring is beneficial. Two objections arise. First, the process seems self-defeating, since it is triggered by learning but ends up giving up plasticity for rigidity. Second, the learning step seems superfluous: why not go straight to the innate trait? To this latter objection three replies have been given. (1) Breathing space (Baldwin). Learning enables the species to survive long enough for the right combination of genes or mutation to occur. This assumes that the ability to acquire a trait is more prevalent than having a gene for it, so the self-defeating argument applies. Also, "do-or-die" situations are very rare. (2) Good learners are genetically closer to the innate configuration for the trait, bringing it within genetic reach. The Hinton and Nowlan simulation which is supposed to show the feasibility of the Baldwin effect actually has this dubious assumption built in to it. The genome is modelled as a string made up of the symbols 0, 1, ?, where 111... is the optimum, and ?-bits leave room for trial-and-error learning. Obviously, good learners (i.e., those who hit upon 111... by randomising their ?s) will generally have more hard-wired 1s than poor learners. So selection for learning and selection for innateness coincide: the model does not leave room for other forms of learning improvement such as skewing the randomisation or increasing the number of trials. (Dennet tries to defend the Hinton and Nowlan model in his chapter, but his argument shows only that selection for learning will bring organisms "closer in learning space" to the desired behavioural trait; this does nothing to resolve the issue of whether this simultaneously means that the organisms will come closer in genetic space to hard-wiring the trait.) (3) Niche construction. The gene is useless before learning. See Deacon below.
Deacon. The niche-construction point of view "breaks the pseudo-Lamarckian mould," for it does not maintain that acquired traits become genetically assimilated. This is a good thing because this simplistic version of the Baldwin effect fares poorly when applied to the evolution of human language (e.g., Pinker). It assumes, implausibly, the ability of incremental genetic changes to reach this predescribed goal; and is also empirically unsuccessful (e.g., innate control of vocalisation has actually decreased in human evolution). Instead one should think in terms of masking. Most genes are masked from selection since they have no substantial phenotypic effect in the current environment. A change in the environment will unmask some of these and mask others. Thus natural selection need not wait for and does not look for the genetic equivalents of learned behaviours; instead learning unmasks a pool of previously silent genes from which support for the learned behaviour can be drawn in a number of ways. For example, when Waddington exposed flies to heat he unmasked a diverse set of previously silent genes scattered in the population, the beneficial ones of which were driven to genetic fixation. The evolution of human language is probably of this type, with the added complexity that the adaptations alters the behaviour in turn.
Several leading evolutionary thinkers discuss the Baldwin Effect in this volume, including Daniel Dennett, Terrence Deacon, and Bruce Weber. The book first illuminates what the Baldwin Effect is and traces its history in evolutionary theory, and then discusses its relevance to current theorizing. I picked up the book because I loved both of Deacon's other books--the Symbolic Species and Incomplete Nature--and he contributes a couple chapters to this volume. I've come away from it with a deeper understanding of evolutionary theory and how evolution might operate.
I appreciated getting dissenting opinions on what the Baldwin Effect is, how it might operate, and whether it matters. The book is the product of a conference, and reading it feels a bit like attending a series of lectures on a topic. If you are interested in how development and learning during and organism's lifetime might influence genetic evolution, this is a great book. It's a particular niche subject, and you probably need to have a basic understanding of evolutionary theory to dive in, but once you do, this book provide a very cool approach. The idea that changes in an organism's development and behavior patterns over its life could either help speed and direct evolution is really fascinating and counter-intuitive. The Baldwin Effect is sort of the tail wagging the dog--organisms learning new skills can effectively change their ecology such that the new skill becomes coded genetically.
Basically, I'd recommend this to anyone who read (and liked) Deacon's Symbolic Species, or anyone who found the above idea exciting. If it's possible for an academic discussion to get you going, this one will.