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10 A Last Dialogue I.M.: You have taken me on quite a journey through the wonderlands of heredity, and I am certainly not going to go through it all again. Instead I want to look at the core of your argument—at the claims that you made at the beginning of the book, in the Prologue. Your first claim was that there is more to heredity than genes. I doubt that anyone will dispute this, even with respect to epigenetic variations (of which most nonbiologists have never heard). Your next claim was that some of the inherited differences between individuals are not just random accidents. Here again, it’s difficult to disagree: new heritable variations can obviously originate in many different ways. Certainly some are the results of accidents, but a lot occur because organisms have evolved systems that bias when, where, and what type of variations occur. Biologists may quibble about the randomness or otherwise of gene mutations, but I think that no one will deny that many epigenetic and cultural differences are nonaccidental. To use your own language, there are many different instructive processes that lead to educated guesses. This almost inevitably means that the next claim that you made—that acquired information can be inherited—must be valid. You told me that evolutionary biologists have a problem acknowledging that something that has been “acquired” can be inherited, because it is associated with Lamarckism, but I find it very difficult to see how anyone can seriously argue that induced or learned epigenetic and cultural variations cannot be passed on. It seems to me that the general case against the inheritance of acquired information should be dropped: as far as the inheritance of acquired information is concerned , your case is convincing. It is the move to what this means for evolution that really matters and is more contentious. It means—and this was your last major claim in the Prologue—that evolutionary change can result from instruction as well as selection. This makes your version of evolutionary theory rather different from the prevalent one. I can show how it differs if I do what you did in 350 Chapter 10 chapter 1, where you highlighted the main features of some of the historical transformations of Darwin’s theory. For your postModern (or is it postpostModern ?) Synthesis, I see the major features as follows: • Heredity is through genes and other transmissible biochemical and behavioral entities. • Heritable variation—genetic, epigenetic, behavioral, and symbolic— is the consequence both of accidents and of instructive processes during development. • Selection occurs between entities that develop variant heritable traits that affect reproductive success. Such selection can occur within cells, between cells, between organisms, and between groups of organisms. Clearly, because you give weight to the epigenetic, behavioral, and symbolic dimensions of heredity, evolutionary change does not have to wait for genetic changes. They can follow. Phenotypic modifications will usually come first. This version of Darwinism certainly has consequences for how we should view patterns and processes in evolution. You indicated several of them. Maybe the most obvious is that by introducing multiple heredity systems and nonrandom variations it is possible to give additional or alternative accounts of evolutionary changes such as the transition to multicellularity and the initiation of speciation. But of more general interest are the implications your version of Darwinism has for the dynamics of evolutionary change. It implies that evolution can be very rapid, because often an induced change will occur repeatedly and in many individuals simultaneously; there is also a good chance that such a change will be of adaptive significance, since it stems from already-evolved plasticity. Even without selection, evolved plasticity will bias the direction of evolution, simply because induced variations are nonrandom. However, as I see it, one of the most important implications of the version of Darwinism that you have espoused is probably that when the conditions of life change drastically , it may induce large amounts of all sorts of heritable variations. The genome, the epigenome, and the cultural system (when present) may all be restructured, with the result that there can be rapid evolutionary changes in many aspects of the phenotype. This summary of your views isn’t exhaustive, I know, but I hope that it is a fair précis of the main claims that you have made. Will it do? M.E.: Yes, although we have to resist a pedantic urge to elaborate. I.M.: Good. So let me now turn to some general...


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