Received views are an important part of our symbolic order. Once it becomes apparent that they cannot possibly be true, it is sometimes a valuable philosophical task to preserve them, since no rational and educated person could actually
believe them. As an example of a critically endangered received view, consider Jerry Coyne's excellent book,
Why Evolution Is True:[T]he process of evolution -- natural selection, the mechanism that drove the first naked, replicating molecule into the diversity of millions of fossil and living forms -- is a mechanism of staggering simplicity and beauty.
The received view is that natural selection is a mechanism or process that shapes all living things, and that the study of natural selection explains a lot about the history of life on Earth. Natural selection makes it possible to treat the billion years of organic evolution as a coherent narrative, making biology an endless reserve of wonder, understanding, and enjoyment.
Matthen and Ariew (
2002,
2009), however, have convincingly argued against the view of natural selection as
a cause of evolution. Their argument applies as well to other characterizations of natural selection: as a process, as a mechanism, as a force. They maintain that natural selection "is a mathematical aggregate of individual events" (2002), "an abstract phenomenon that obtains in all population histories" (forthcoming). They assert that
variation (in a given population, in a given environment)
causes evolutionary change, but deny that
natural selection causes evolutionary change. Obviously, it is not variation
alone that brings about evolutionary change, but once natural selection is understood as the outcome of very many possible interactions amoung traits, individuals, and environments, to be assessed on a case by case basis, the notion of "selection-as-process" becomes untenable and all we are left with is "selection-as-outcome". This sounds like a serious blow to the received view of natural selection. One may wonder whether an alternative account can save it.
As one of the foremost population geneticists, Coyne cannot ignore the discrepancies between the "vernacular" view of natural selection (as process, mechanism, or cause) and what his science tells him. Here is how he introduces the crucial idea:
The idea of natural selection is not hard to grasp. If individuals within a species differ genetically from one another, and some of those differences affect an individual's ability to survive and reproduce in its environment, then in the next generation the "good" genes that lead to higher survival and reproduction will have relatively more copies than the "not so good" genes. Over time, the population will gradually become more and more suited to its environment as helpful mutations arise and spread through the population, while deleterious ones are weeded out. Ultimately, this process produces organisms that are well adapted to their habitats and way of life.
Thus, Coyne avoids an explicit definition of natural selection: what he describes is an abstract process leading to adaptation. To me, it seems that we all know (well,
we may still be a minority since many philosophers appear to think differently) that natural selection cannot be construed as one of the customarily relevant things -- causes, forces, mechanisms, processes -- that can be inserted at the proper place, in a larger account of how things work, in order to do explanatory work.
Since I take Matthen and Ariew's views to be correct, I find it hopeless to insist on natural selection as 'something' behaving like an agent, a designer, a partial optimizer, or even a sieve (as in the rather frequent account of variation
followed by selection
resulting in evolutionary change). Should this (correct) view become dominant, however, we should face the dire consequences: educated people would have no reason to believe that there is a simple, understandable explanation for the whole of evolution (does anybody know of one such explanation, by the way?), and we should stop praising such excellent books as Coyne's. It could be a philosophically interesting issue (and I'm inviting comments on this as well) to see whether we could maintain the association between natural selection and simplicity, beauty, amazement, or ideas-that-change-everything. Clearly, "selection as outcome" and "variation as cause of evolutionary change" cannot hold to the task.
Whatever the broader philosophical and "political" implications, my interest here is in showing how the received view of natural selection might be preserved. I don't know whether Matthen and Ariew would agree on my interpretation of their work, but I would like to call attention to the fact that although natural selection is indeed a statistical aggregate (a pattern of distribution?) the term alludes to (suggests?, points to?) a causal story about how the aggregate came about (without actually
requiring the provision of a causal story). This is my way of seeing the significance of the authors' "hierarchical realization model" of how evolutionary influences combine.
Since I am not sure I understand the model, I will not elaborate on it. I'll just try to redress the received view of natural selection in a way that can highlight a possible role for the model:
- (some) naturally occurring variations improve the organism's ability to survive and reproduce in a given environment;
- these functional improvements (often qualitative) are someway translated into a quantitative, statistically significant difference in reproductive rates;
- there is an abstract, mathematical relation between higher reproductive rates and the spread of favorable variations (the outcome).
Here, an analysis of function/causal roles is mainly confined to 1, while the mathematical aggregate we call natural selection is the direct outcome of 3. It is in 2 that the hard work is done, the "work" of converting the interactions among functional variations, other changes in the organism (e.g., changes in fertility or in mating behavior), and environmental changes as well, into quantitative differences in reproductive rates. Whether the hierarchical realization model can accomplish all this work, I don't know, but it seems promising.
In place of a conclusion, a tendentious question: in view of the symbolic importance of natural selection, why don't they just call it "the hierarchical realization model of natural selection"?