The last post identified special conditions that increase the chances of natural selection (carefully construed) serving as an explanation of the historical change in the frequency of one character. From a knowledge of biology, we should agree that these special conditions are rare or not necessarily generalizable. The consequences for evolutionary theorizing have been several. Biologists (and others) often:
- collapse “selection,” using the term as a synonym for differential representation of characters[i]
- rely on claims about current functionality without evidence of historical (temporal) change;
- accept milder standards of evidence (e.g., the historical process has been observed in some cases of natural selection, so it is plausible that it occurred for the character whose current function has been demonstrated; or one works at a coarse level of resolution of characters, environments, and change so that departures of the detailed mechanisms from the special conditions are not evident[ii]);
- invoke repeatedly the same few textbook cases of natural selection; or
- perform laboratory or other experimental work in which selection literally, not metaphorically, takes place.
I concede that applying the strong standards of evidence I have outlined may result in few natural selective accounts qualifying as adequate historical explanations. Nevertheless, it should also be recognized that squeezing evolutionary change so it can fit the special conditions above has the effect of discounting many important aspects of biology:
- characters that are not singled out in living activity of organisms;
- the development or the reconstruction during an organism’s lifetime of its characters, over and above the transmission of genetic and other material to the zygote (and in contrast to snapshots of characters at some point of time in the lifecycle);
- the broader conditions for “recurrency” of characters, which depend not only on the genetics implicated in the development of characters, but also on the persistence of environmental conditions at least insofar as the organisms modulate or “construct” those conditions (Lewontin 1982, 1983, 1985);
- the contribution of developmental and ecological flexibility to the evolutionary origin of characters (Taylor 1987)[iii]; and, more generally,
- the structured, yet changing, ecological dynamics to which organisms both respond and contribute.
In short, characters are part of structured processes. For some biologists and philosophers of biology these complexities of biology mitigate against the coherent accumulation of change over time; they believe that only when the special conditions more or less apply does evolution lead to identifiable adaptive outcomes. Others attempt to incorporate some of these aspects of biology by adjusting the theory of natural selection, as in, for example, frequency-dependent selection. This tinkering, however, preserves room for the almost conventional moves back and forwards in evolutionary thought among forward speculation and backward fitting.[iv] My preference is to free ourselves from the restrictive, and thus widely misused, form of the natural selective explanation.[v]
In the next post in the series I include an example of the contribution of developmental and ecological flexibility to the evolutionary origin of characters. Then I return to the original question of what it might look like to make evolutionary studies more ecological.
Keller, E. F. and E. A. Lloyd (Eds.). (1992). Keywords in evolutionary biology. Cambridge, MA: Harvard University Press.
Lewontin, R. C. (1982). Organism and environment. In Learning, Development, and Culture, ed. H. C. Plotkin, pp. 151-170. New York: John Wiley & Sons.
Lewontin, R. C. (1983). The organism as the subject and object of evolution. Scientia 118: 63-82. Reprinted in The Dialectical Biologist, ed. R. Levins and R. C. Lewontin, pp. 85-106. Cambridge, MA: Harvard University Press.
Lewontin, R. C. (1985). Adaptation. In The Dialectical Biologist, ed. R. Levins and R. C. Lewontin, pp. 65-84. Cambridge, MA: Harvard University Press.
Taylor, P. J. (1987). Historical versus selectionist explanations in evolutionary biology. Cladistics 3: 1-13.
Another extract from “From natural selection to natural construction to disciplining unruly complexity: The challenge of integrating ecology into evolutionary theory,” in R. Singh, K. Krimbas, D. Paul & J. Beatty (eds.), Thinking About Evolution: Historical, Philosophical and Political Perspectives, Cambridge: Cambridge University Press, 377-393, 2000.
[i] A variant of this is the idea that a character could be the cause of natural selection for organisms having that character if the character has a positive effect on survival and reproduction averaged over the range of contexts in which the character occurs. This conceptual move underwrites theories about natural selection of sub-organismic units and sometimes, super-organismic units.
[ii] In the hypothetical example in an earlier post in the series, if we had not noticed the plant’s relative that had the same angle without the hummingbird pollinator, but we were aware of the ancestor, natural selection would have been both functionally and temporally plausible. At some point, however, we balk at allowing a lessening of resolution to support natural selective explanation. We know, for example, that it is too coarse to correlate bird feathers both functionally and temporally to the bird lineage’s move into the air.
[iii] In order to fully account for the direction of the observed historical change one should—even in a natural selective explanation—study the origin of the character. This explanatory requirement might account for biologists’ reliance on another special condition, namely, the origin of characters by mutation or recombination, which make this origin random with respect to environmental circumstance.
[iv] As evident, in particular, in debates about “fitness,” units of selection, and levels of selection (see relevant entries in Keller and Lloyd 1992).
[v] It follows that I also propose abandoning the concept of adaptation, in both its senses, i.e., the character that has been the causal focus of a natural selection account and the process of its evolutionary development. My thinking along these lines drew at a key stage on Lewontin’s critique of the concept (see Lewontin 1983).