Reference:
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.
(250)
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liane.gabora[at]ubc.ca
http://www.vub.ac.be/CLEA/liane
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.
References
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.