This week we can all enjoy the hotly anticipated debut of one of Philosophy's first open-access general journal Ergo, for which we have the fantastic Franz Huber and Jonathan Weisberg of Toronto to heartily thank.
Of course, we already have the Philosopher's Imprint, which provides totally free refereed journal articles. But Ergo is the very first to try and include section editors from all areas and traditions within philosophy. They can further boast a triple-anonymous review policy and will publish data about their submissions and turn-around times.
Spearheading its launch comes a fine paper scrutinising an analogy which has been getting a bad rep in philosophy of biology lately. Velasco & Hitchcock's Evolutionary and Newtonian Forces asks how far we can go by comparing natural selection, drift and other evolutionary phenomena to physical forces such as gravity.
Against defenders of the statistical view of selection, for whom evolution is just the net aggregate of everyday birth and death events, rather than being the outcome of any overarching force, the authors claim that the analogy is in fact sound, so long as we let go of gravity being the sine qua none of dynamical forces. If, instead, we consider forces such as friction and elasticity, then we see that those features, whose absence supposedly disqualifies selection and drift from being Newtonian, are actually lacking in some of Newton's paradigm forces too. The criticisms, in other words, "rest on false presuppositions about what a theory of forces must look like." This is good news for all those, such as Elliott Sober, who have long argued that natural selection is a genuine cause of evolution, because our notion of causality finds perhaps its strongest exemplars in good old-fashioned Newtonian causes of motion.
Our chat about natural selection gets metaphorical in various ways - genes as agents, traits as designed, etc. One of the most central and, for me, vivid figures of thought casts natural selection Herself (She is always female) as an agent. I think of Her as being much like the wispy magical hand from the national lottery adverts, coming down and choosing organisms to be the lucky ones that make it. We could equally spell the idea out as some sort of giant boot that squashes the not-good-enough (Final destination style?) but I prefer the happy version. Either way, natural selection acts, She chooses, She favours, etc etc.
More precisely, these critics (in particular Denis Walsh, Tim Lewens, Mohan Matthen and André Ariew) hold that "The analogy between Newtonian forces and evolutionary 'forces' such as natural selection, drift, mutation and migration is misleading." Against this, Velasco & Hitchcock maintain that there is no danger of being misled, so long as we are careful to match up evolutionary forces to the appropriate Newtonian analogs. Natural Selection, for example, matches up rather nicely to friction or to the elastic force, while migration and mutation approximate gravity. The authers give a careful, detailed refutation of several supposed sources of disanalogy, including;
- Isolability - whether or not the force can be conceived as acting independently of others.
- Source laws - which spell out the way in which the force acts independently of any body actually being acted upon.
- Composition of forces - whether we can compute the net effects of forces acting in concert (Sober 1984).
- Tertium quid - whether the process in question is a distinct causal variable acting as an intermediate link in a causal chain.
The source law requirement is satisfied by any zero force law - usually the Hardy-Weinberg equilibrium, but Brandon & McShea's ZEFL would work too. NB there are a lot of laws required, for a subject which is often claimed to involve none. And as someone who thinks mostly about case studies involving either plants or bacteria, I feel a bit twitchy about anything that puts fundamental importance on the Hardy-Weinberg equilibrium, which only applies to diploid organisms. I wonder if Lewontin's conditions couldn't act as a general source law for evolutionary forces?
One outstanding wrinkle in all this: while it's true that the argument is often framed as being about whether natural selection is comparable to a Newtonian force, and true that friction and the elastic force are definitely Newtonian forces, there might be a legitimate sense in which a defender of a statistical view could say 'but those forces are different.' As Velasco & Hitchcock acknowledge, friction and elasticity are usually thought of by physicists as emerging "from the aggregate statistical behaviour of more elementary forces in certain kinds of system." It's easiest to see this with friction - roughly friction is what we call the resistance offered to a body by the stickiness of some surface. The stickiness of the whole surface is a sum of the stickiness of the molecules from which it is composed, which ultimately boils down to weak and strong nuclear forces between subatomic particles. So in this sense we might say that friction supervenes on more basic forces, rather than having any causal oomph of its own.
But this is grist to the statistical view's mill, we might say. They argue that natural selection supervenes on more basic causal events, without adding any extra causal power of its own. So these critics might happily accept that evolutionary forces are analagous to non-fundamental Newtonian forces, whilst holding their ground on the claim that natural selection is not causal.
Velasco & Hitchcock's response to this possibility is interesting. They point out that actually "the situation is a bit tricky, since the details of how these forces arise are not completely understood. Moreover, the explanation will likely take us out fo the realm of Newtonian mechanics......so it may be fair to say that from the perspective of elementary Newtonian mechanics, friction and spring forces are basic."
I suppose what the authors want to do here is put pressure on the idea of some level being more basic or elemental than another. If we mean epistemically, then friction has priority over electromagnetic forces, since it is better understood. Further, we could argue for friction as emergent rather than being reducible to lower level forces, in so far as our lack of understanding about how the electromagnetic forces sum makes us unable to compute the friction they give rise to. More simply, however, there is no point complaining that selection isn't force-like on the grounds that there is something metaphysically ambiguous about its status in relation to the lower-level events with which it is intimately related, given that analogous metaphysical concerns accompany the more-and-less fundamental physical forces. Gravity is the paradigm spooky action-at-a-distance. Quantum entanglement, wtf? If there is anything magical about thinking of natural selection as an overall force producing all the multifarious births and deaths that we actually observe, then it is in very good company lumped in with physical forces.
When we compare natural selection, drift, mutation and migration to the strange, complex and only incompletely understood forces of actual physics, as opposed to the simplified forces of folk physics, the obvious disanalogies evaporate. In fact I'd guess that the straw man is actually what my A-level physics teacher, the excellent Mr Drum, used to call 'balls in a box.' The simplest kind of mechanics, the kind most people have little trouble making predictions about, concerns the behaviour of snooker balls. In Newton's mechanistic paradigm, all physical events were to be understood as arising out of the collisions of corpuscles. His laws act on these corpuscles much as snooker cues push snooker balls around on a table. Evolution can similarly be conceptualised in terms of the motion of particles, where the particles are organisms whose 'collisions' - their fitness-affecting interactions, in other words, form macro patterns. Evolutionary forces dictate the eddies and currents, some sections of the stream moving faster than others, some swirling into deadends, others branching off.
Velasco & Hitchcock say "The analogy succeeds, in part, because Newtonian forces and evolutionary forces are both heterogeneous. Gravity is very different from friction, and natural selection is very different from migration." I would add that it succeeds because actual physical forces, unlike folk physical forces, are actually pretty ambiguous and badly understood. In both cases, the notion of a force as some sort of power posessing a magnitude and a direction, like a gust of wind or the slap of a hand, is a heuristic by which we attempt to get a handle on the messy underlying reality.