Warning: Biology wonkage, proceed at own risk
On the forum at Richard Dawkins’s site, I came across an exchange between Dawkins and a forum member describing “natural selection” as the “driving force of evolution”.
I’m bothered by this usage. For one thing, it seems like the kind of thing that can contribute to the rancorous debates in biology that sometimes strike me as more semantic than scientific. However, it is also possible that I’m not quite understanding what the intent of the phrasing is.
The discussion at Dawkins’s site was started by “Hyrax”, who was puzzled by the assertion that evo-devo poses a challenge to the theory of natural selection. In a question to Dawkins, he/she/it/not-rodent writes:
I have been involved in a lot of debate over the subject of ‘Evo Devo’ and similar ideas that claim to usurp natural selection as the principle driving force of evolution.
From Dawkins’s response:
Of course evo-devo doesn’t usurp natural selection, any more than a car’s engine usurps the driver. There are alternatives to natural selection, and the obvious one is random genetic drift. In its molecular guise of Kimura’s ‘neutral theory’ it is plausible as an alternative driving force of evolution. Indeed, I think it is quite likely that the majority of evolutionary change at the molecular level is neutral. But natural selection is the only known evolutionary driving force that is capable of generating adaptation.
Perhaps this is just a matter of definitions, but, by my understanding, natural selection is an utterly passive process; it can’t “drive” anything. Evolution requires variation — genetic mutation, recombination, epigenetic twiddling. The possibilities manifested out of that variation are then filtered based on environmental pressures (broadly conceived). That filtering process is what is called “natural selection” — it does not “drive” evolution any more than a vacuum cleaner filter is a source of suction.
Note what Dawkins is saying: natural selection generates adaptation. AFAIK, natural selection can not “generate” anything at all — it can only, well, select. An “adaptation” is just some bits of variation that have survived and can be retrospectively crowned as more useful — for the situation under consideration — than the available alternatives that didn’t survive.
So I’m curious: why does this metaphor stay around? Its convenience as a turn of phrase overcomes the degree of deficiency it bears from being misleading? Dawkins seems to use it quite unselfconsciously, and I know I’ve seen it in other places. Does anyone else find it nettlesome, as I do, or am I being hyper picky?
I have wondered whether it arises from something in the mathematics used to describe “fitness landscapes”, i.e. that something about the mathematics somehow makes the metaphor work when applied in that context. It also seems possible that there is some kind metonymy going on here where the forces attributable to selection pressures becomes attributed to selection itself.
I’ve long been a bit suspicious of Dawkins’s metaphors. I tend to find Gould and Lewontin more to my liking. And while I can’t recall whether or not Dawkins has ever engaged in quite the kind of ad hominem foolery against Gould that Dennett (among others) has, I don’t know that he’s ever distanced himself from it either. The weird thing is that I’m not even sure there was truly a substantive scientific issue involved in the big Dawkins vs Gould debate. I haven’t traced it into all its details, but I’ve had the impression at times that it was just a case of “lumpers vs splitters”. That is, Dawkins — the lumper here — sought to designate all the processes involved in evolution Darwinian, and Gould wanted to keep the term Darwinian for just a certain set of core processes, but that in the end the underlying phenomena were not much in question.
From Richard Lewontin’s The Triple Helix: Gene, Organism, and Environment (pp 3-4):
It is not possible to do the work of science without using a language that is filled with metaphors. Virtually the entire body of modern science is an attempt to explain phenomena that cannot be experienced directly by human beings, by reference to forces and processes that we cannot perceive directly because they are too small, like molecules, or too vast, like the entire known universe, or the result of forces that our senses cannot detect, like electromagnetism, or the outcome of extremely complex interactions, like the coming into being of an individual organism from its conception as a fertilized egg. Such explanations, if they are to be not merely formal propositions, framed in an invented technical language, but are to appeal to the understanding of the world we have gained through ordinary experience, must necessarily involve the use of metaphorical language. [...] Indeed, the entire body of modern science rests on Descartes’s metaphor of the world as a machine which he introduced … as a way of thinking about organisms but then generalized as a way of thinking about the entire universe. [...]
While we cannot dispense with metaphors in thinking about nature, there is a great risk of confusing the metaphor with the thing of real interest. We cease to see the world as if it were like a machine and take it to be a machine. The result is that the properties we ascribe to our object of interest and the questions we ask about it reinforce the original metaphorical image and we miss aspects of the system that do not fit the metaphorical approximation. As Alexander Rosenblueth and Norbert Weiner have written, “The price of metaphor is eternal vigilance.”