In the first of two posts discussing the role of scientific metaphor in evolutionary theory, we look at what is meant by “selection”.
The trouble with trying to ferret out what Stephen Jay Gould called “canonical imagery” in science, and especially in evolutionary studies, is that science is thoroughly dependent upon metaphor – and even more so when scientists try to explain theories to a wider audience. Gould stated that he knows “no other subject so distorted by canonical icons: the image we see reflects social preferences and psychological hopes,” rather than data or theory.
But this critique doesn’t go far enough, since the theories themselves are equally packed full of metaphors with just as much power to distort thinking if not considered carefully. Gould notes: “If icons are central to our thought, nor peripheral frills, then the issue of alternative representation becomes fundamental to the history of changing ideas in science”. It is this issue of “alternative representation” that we need to address in considering the myths of evolution – because even if we believe that the facts don’t change, the way we present those facts does change, and different metaphors guide thinking in radically different ways.
Two of the central metaphors in contemporary evolutionary theories have been with the field more or less since its inception with Darwin: the metaphors of selection and of fitness. It is almost impossible to have a discussion of the subject without using these words, yet the terms are as much “canonical icons” as the Ladder of Progress (satirically pictured above) that Gould justifiably challenged. ‘Selection’ was only ever a metaphor, and in so much as the ‘fitness’ implied by Darwin’s theory can be rendered meaningful, it must be understood as a useful fiction. There is just as much risk of being misled by the imagery these terms conjure to mind as anything else in science, and yet it seems nearly impossible to excise them from the evolutionary lexicon.
Darwin was acutely aware of the fact that his use of ‘selection’ in Origin of Species was a metaphor. He received letters from Alfred Russel Wallace, the naturalist who was postulating a very similar theory at the same time as Darwin, expressing concern that the term ‘natural selection’ was too anthropomorphic, leading to a personification of nature as “selecting” or “preferring”. Philosopher Michael Ruse notes in this regard:
In his heart, Darwin seems never to have wavered, and he responded to those who criticized the term “selection” by pointing out that it was a metaphor, and who can do science without being metaphorical? “No one objects to chemists speaking of ‘elective affinity,’ and certainly an acid has no more choice in combining with a base, than the conditions of life have in determining whether or not a new form be selected or preserved.”
John F. Haught suggests that Darwin might have been more flexible in this regard, noting that the later Darwin writings sometimes seems to offer “natural preservation” as more suitable than “natural selection”, but whatever Darwin’s feelings the term selection has certainly stuck. Darwin publicly dismissed any problems with the metaphorical aspect of the term on the grounds that science was effectively impossible without metaphorical thinking, but this does not mean Darwin was blind to the kind of constraints on thought that specific images convey. He avoided using the word ‘evolution’ precisely because he didn’t want to take upon the baggage the term had already acquired in terms of conveying a sense of progress and destiny. He seems to have believed, rightly or wrongly, that the term ‘selection’ could sidestep this kind of implication.
In order to fully understand contemporary evolutionary theories, it is necessary to separate – in as much as this is possible – the metaphors from the facts, the myths from the models. A conscientious audit of metaphorical terms like ‘selection’ and ‘fitness’ has much to show us about both evolution and about science in general, but this kind of critique is usually avoided, perhaps for fear of adding fuel to the fire being tended by opponents to evolution. This concern is not warranted. People are perfectly entitled to reject a particular scientific theory for whatever reason they choose, and they are especially free to object to those theories that they suspect have been ideologically contaminated. Frankly, there is little doubt that the presentation of evolution in public has been distorted in this way, and this by people on both sides of the fence. A defence of evolutionary studies should rest on an honest understanding of the issues, and this necessitates an acceptance of the role of imagination in its operation.
When I call ‘selection’ imaginary, or suggest that ‘fitness’ is a fiction, I do not mean that all evolutionary theories are mere figments, but rather that these terms cannot be understood without reference to imagination. Metaphor is an imaginative activity – the process of thinking about one thing by comparison to another. Science, as Darwin recognized, thrives on this kind of analogical thinking, because science – in common with the arts – is fundamentally an imaginative activity. True, much of a research scientist’s time is absorbed in experiments, observation and data, none of which is enormously creative. But the experiments being conducted, and even more so the concepts that motivate those experiments, all began life as imaginative fictions. Every theory inevitably implies a story.
The fiction in which the term selection gets its meaning is that whereby it is as if something has made a decision that selects some animals and not others to survive (for natural selection) or to reproduce (for sexual selection). Because selection is intended as a scientific metaphor, it is generally considered poor form to indulge in speculations as to the obvious consequences of the fiction e.g. if we say that Mother Nature does the selecting, we’ve brought in a mythic figure (‘Mother Nature’) into what was supposed to be a sober, scientific term. This was precisely Wallace’s objection to Darwin’s use of ‘selection’ – these kinds of extrapolations follow all too easily. Darwin’s counter was that it is useful to think in terms of selection, the story does some valuable work for us in terms of focusing our attention onto what is happening.
This brings us to the other important part of Darwin’s fictional representation of how creatures change over time: fitness. Darwin didn’t actually use the term, but did make reference to individual animals being “fitter” or being more or less “fit” than others; it is from this informal discussion of a comparative scale of “fitter” animals that the modern concept of fitness develops. Philosopher André Ariew and geneticist Richard Lewontin are very clear on the role of metaphor in this part of Darwin’s ideas:
Different individual members of a species, then, ‘fit’ into the environment to different degrees as a consequence of their variant natural properties, and those that made the best ‘fit’ would survive and reproduce their kind better than those whose ‘fit’ was poorer. The word ‘fit’ (‘fittest’, ‘fitness’) is a metaphorical extension of its everyday English meaning as the degree to which an object (the organism) matches a pattern that is pre-existent and independently determined (the environment). This metaphorical lock-and-key fitting of the organism into the environment is reflected in the modern concept in ecology of the environmental or ecological ‘niche’ that species are said to ‘occupy’.
We can see here the fiction that Darwin was using in his original conception in Origin of Species: some animals ‘fit’ better into their environment, and these are ‘selected’ to survive. It is as if the world is a partially completed jigsaw, with a certain number of gaps for extra pieces. Those pieces that fit into the jigsaw persist, while those that don’t fit are discarded. The heuristic value of thinking this way is comparatively clear, and the benefits can be conveyed irrespective of whatever imaginative gloss we add to the core metaphor – the jigsaw image I just proposed, for instance, or Ariew and Lewontin’s lock-and-key image.
However, in the decades since Darwin, the term fitness has expanded to take onto its metaphorical shoulders far more than Darwin ever intended. In the words of philosopher of biology, Elliott Sober, fitness has “two faces”. It not only describes the relationship between an animal and its environment, as described above, but leads a double life as a mathematical term used in formulating predictions. In Sober’s words: “Fitness is both an ecological descriptor and a mathematical predictor.” Trouble is, this double life threatens to wear fitness rather thin; the strain of pretending that the mathematical face is still a fit to Darwin’s original use might just be too much for it to bear.
Extracted from the draft manuscript of Myths of Evolution, due from Zero Books in 2012.
Next week: Fitness