Gabora, L. (2007). Epigenetic and cultural evolution are not Darwinian. Commentary on E. Jablonka & M. J. Lamb, Synopsis of 'Evolution in Four Dimensions'. Behavioral and Brain Sciences, 30(4), p. 371.
Abstract: The argument that heritable epigenetic change plays a distinct role in evolution would be strengthened through recognition that it is what bootstrapped the origin and early evolution of life, and like behavioral and symbolic change, is non-Darwinian. The mathematics of natural selection, a population-level process, is limited to replication with negligible individual-level change, i.e. that uses a self-assembly code.
The authors have produced an admirable synthesis showing how processes with vastly different underlying mechanisms constitute important, interrelated facets of evolution. Ironically, though their intent is to highlight Lamarckian aspects of evolution, their framework discourages it. If genetic and cultural evolution were viewed not as components of one big four-dimensional evolutionary process but two intertwined evolutionary processes, one primarily Darwinian and the other primarily Lamarckian, there would be no need to rely heavily on genetic assimilation as the means by which behavioral and symbolic systems exert lasting evolutionary impact. (They affect cultural evolution regardless of whether they affect genes.) The focus on genetic assimilation leads to a gradualist scenario for the transition to symbolic thought that is unsupported, as is the contention that symbolic thought followed naturally from possessing a larger brain (p. 304). Leakey (1984) writes of human populations in the Middle East with brains that were modern in shape and size, but virtually nothing in the way of symbolic culture, and concludes "The link between anatomy and behavior therefore seems to break" (p. 95). This suggests that encephalization was followed by enhanced capacity to make use of a larger brain. To my mind the most reasonable explanation for the transition to symbolic thought is that genetic mutation facilitated the capacity to subconsciously shift between focused and defocused attention, thereby shifting between analytic thought---conducive to logic and symbol manipulation---and associative thought---conducive to analogy and 'breaking out of a rut' (Gabora, 2003). Onset of this capacity would confer upon the mind both hierarchical structure and associative richness conducive to language and other complex tasks. Another hypothesis is that once culturally generated artifacts created sufficient change in the environment, cultural evolution simply snowballed, without any underlying genetic change at all (e.g. Donald, 1991, 1993). Explanations such as these that do not rely on genetic assimilation cannot be ruled out.
The authors' reason for treating behavioral and symbolic transmission as distinct dimensions is that behavior must be displayed, whereas symbols can transmit latent information that skips generations (p. 202). This distinction breaks down when one considers real transmission amongst creative individuals operating in different contexts with different abilities. Consider the following simple scenario. Ann pats the cat. Bob, who is sitting in a chair holding a baby, sees this and nuzzles the cat with his foot. Cindy, who sees Bob but not Ann, pats the cat. Thus the patting skipped a generation. The other rationale given for treating them as distinct, that symbols must be taught whereas behavior need not be, is also not strictly true. In my view, both behavior and symbolic use reflect the non-Darwinian cultural evolution of a worldview: the individual's means of internally construing the world and his or her place in it. At any rate a stronger argument should be made for treating them separately.
Throughout the book the authors assume that epigenetic, behavioral, and symbolic change proceed through natural selection (a move Darwin himself never made). They speak of "selection of epigenetic variants" (p. 359), "a change in the parents' behavior that generates a new behavioral variant" (p. 166), and refer to their theory as a "version of Darwinism" (p. 356). However, for a process to be Darwinian, inheritance of acquired characteristics must be negligible compared to change due to differential replication of individuals with heritable variation competing for scarce resources. What necessitated the theory of natural selection, a theory of population-level change, is that acquired traits are not inherited from parent to offspring at the individual level. In a world where, if a cat bites off a rat's tail, the rat's offspring are not born tail-less, how does one explain how change accumulates? That was the paradox Darwin faced, the paradox for which natural selection provided a solution. There is no such paradox for early life nor culture, because they do not replicate using a template, a self-assembly code that is both actively transcribed to produce a new individual, and passively copied to ensure the new individual can itself reproduce. The individual may change, but the passively copied code does not. The mathematical framework of natural selection is not transferable to evolutionary processes that are not code-driven (Gabora, 2006). Such processes are correctly described in terms of 'actualizing potential' rather than 'selecting amongst variants'.
I suspect many will find the arguments concerning the key role played by epigenetic processes ultimately unconvincing, due to the paucity of heritable epigenetic change. (How much of what we or Jaynusians learn or acquire in a lifetime is transmissible through the germ line?) The authors' position could be strengthened by considering recent work indicating that epigenetic inheritance not only began in simple unicellular organisms (as they rightly point out); it was the means by which early life evolved (Gabora, 2006; Vetsigian, Woese, & Goldenfeld, 2006). Given the book's breadth, it is understandable that the origin of life is considered "outside the scope of this book" (p. 320). However to me this felt like going on a treasure hunt, peeking down the alley that holds the treasure, and passing it by. When one realizes that there existed a time in which self-organized structure replicated (albeit sloppily) through autocatalysis prior to template-mediated replication, one appreciates that epigenetic processes are what provided the means by which this primitive structure evolved the genetic code itself.
The authors' contention that epigenetic processes constitute a distinct and important dimension of evolution is indeed strengthened by the realization that they cannot be described by natural selection, which is intimately tied to the genetic code. This also gives us a clear rationale for treating cultural evolution, a non-Darwinian process with behavioral and symbolic components, as distinct from genetic evolution (and the epigenetic processes it grew out of). Indeed it has been suggested that cultural evolution operates through a mechanism very similar to that by which early life evolved (Gabora, 2004). The evolving entity, the worldview, is (like a primitive lifeform) integrated, self-organizing, and self-mending.
Donald, M. (1991). Origins of the modern mind, Cambridge, MA: Harvard University Press. (Precis with commentary, 1993, Behavioral and Brain Sciences, 16(4), 737-791.)
Gabora, L. (2003). Contextual focus: A cognitive explanation for the cultural transition of the Middle/Upper Paleolithic. In (R. Alterman & D. Hirsch, Eds.) Proceedings of the 25th Annual Meeting of the Cognitive Science Society, Boston MA, July 31-August 2. Hillsdale NJ, Lawrence Erlbaum Associates.
Gabora, L. (2004). Ideas are not replicators but minds are. Biology & Philosophy, 19(1), 127-143.
Gabora, L. (2006). Self-other organization: Why early life did not evolve through natural selection. Journal of Theoretical Biology, 241(3), 443-450.
Leakey, R. (1984). The origins of humankind. New York: Science Masters Basic Books.
Vetsigian, K., C. Woese, & Goldenfeld, N. (2006). Collective evolution and the genetic code. Proceedings of the National Academy of Sciences USA 103, 10696-10701.