Friday, July 25, 2014

On the mythology of natural selection. Part IX: What would it mean if selection really were deterministic?

Today's post will have to do with the question, "What is cause?". This will be a bit abstract, but I hope it will be at least somewhat understandable.

We have been writing about the subject of genetic determinism and its twin, deterministic natural selection.  Pure determinism means that when I know an organism's genotype I can perfectly predict its traits and that given different organisms' genotypes I can perfectly predict their relative fitness (reproductive success).  It's one thing to consider skylarks and oak trees in this regard, because nobody really cares; but now we know that humans are part of Nature rather than separate creations, we naturally want to apply the same principles to ourselves as we do to plants and other animals.  And though issues about determinism apply to all of Nature and its evolution, it's the way they hit home that makes it important for the human sciences, above all, to realize the implications of how we view ourselves in light of our ideas about evolution.

Some people object to suggestions that natural selection might not be genetically deterministic--that there might be other aspects to the organisms' traits, such as environment which in the case of humans includes their culture.  An unstated or perhaps even not even fully aware objection to any challenge to genetic determinism is that if you open the door, even a tiny crack, to the uncertainties of probabilism or environmental, or in the case of humans to cultural effects, you'll venture off into 'softer' non-scientific views of Nature.   That point of view suggests that we can peer into genomes to see individuals' or groups' inherent worth, as one can fancy that Nature in the form of selection sees and has seen it.

To use humans further to illustrate the point, the fact that we wear coats in winter and domesticate our food sources would seem to be manifestly obvious examples of niche construction.  To push this further, can any sane scientist argue that, say, Doric architectural columns were built because of specific genotypic differences between their architects and the architects who built Ionic columns?  If not, and if it's not cultural (environmental), what is the 'cause' of the style differences?  An honest assessment raises the question how far can assertions of genetic determinism go, and if the door is opened to cultural/environmental causation, where do you stop, if you can't read individuals' traits off their genomes?

Doric Order of the Parthenon (Wikimedia)
Ionic Order (Wikimedia)

But let's think a bit deeper than this superficial bit of sociocultural generalizing.

If evolutionary fitness were truly determined
In this series on natural selection we've often accepted, temporarily for the sake of argument, a proposition that genetic causation, and hence selection really are perfectly deterministic.  That means selection reads two organisms' genotypes, say, and determines everything about them, including who will win the evolutionary race, in the same law-like way that gravity pulls objects towards each other as a deterministic force.  Let's again take this as true for the purposes of argument, and see its consequences.

First, such determinism if true would mean that everything--everything--about every organism is perfectly predictable.  And if what happens is perfectly determined and predictable, then we can follow what's here today, using the force-like laws that make it predictable, back as well as forward in time, so that in fact everything--everything--is just following those laws and hence was already predictably inevitable from the instant of the Big Bang.  Of course, to actually predict everything you'd have to have all the information, perfectly understood, which in turn requires that you be above or out of the system whose properties you want to know: in a sense you need to know more than everything there is to know.  Arguing that position is logically no different from just saying "God willed it to be that way." It's not science, and it doesn't explain anything.

Even total genotypic predictability, however, should give no solace to genetic and darwinian determinism. That's because if everything were pre-determined, then there is no 'natural selection': there's no random mutation screened competitively by the environment, because winners and losers and their genotypes were always already in the works waiting to happen.  In that case, 'evolution' really holds only its original sense of the world: an 'unrolling' of what's already there.  Even before its conception, the future rabbit was doomed to be caught by this particular future fox, in the same sense that we would not say the apple 'evolved' onto Newton's head, but that it just followed the law of gravity.  If so, everything including the misleading (under our working assumption of determinism) evidence of chance (genetic drift, mutation) is simply predetermined!  Unfortunately, perfect determinism cannot be tested or proved, so we're not any further along in our understanding.

The role of 'chance'
The point of science is to understand causation and that is essentially the same as making predictions of the future from observations in the present.  However, even if perfect determinism were the case, things are not predictable in the usual informal sense of deterministic world-views: since we can't have perfect information, only the artifacts of measurement and sampling make a perfectly deterministic world seem non-determined.  We have to make assumptions about when, where, how, and how much our measurements were off--about the distribution and probabilities of what would only appear to be chance.  And those probabilities are themselves determined in some way, if you think about it.

We know from such things as chaos theory among others, that even tiny measurement errors can lead predictions to be completely wrong in a way that's largely unpredictable and untestable (this is often referred to as the 'butterfly effect').  From A to Z we face measurement errors and make assumptions about phenomena that lead us to treat them as driven by chance even if they were entirely pre-determined.

We thus seem to face an inevitable degree of unpredictability even if we're in a wholly deterministic cosmos.  And many physicists argue that the cosmos in fact is at its most fundamental level irreducibly probabilistic (this, for example, in quantum mechanics).  In turn, this means that things cannot be predicted more precisely than by probability--and the conditions under which we can actually know what that probability is, or how it limits the accuracy to which we can aspire, are very limited.

And what if life and its working-out really do have a fundamentally probabilistic component--that is, selection, mutation, mate choice, and genetic interactions with environments?  In that case, at present we generally have scant knowledge of what such probabilities actually are or even how to identify them.  In other words, whether life is or is not wholly deterministic, it at least inescapably appears to be probabilistic. And that means that individuals' natures cannot just be read off a DNA sequencer.

Either, neither, both!
There is some strangeness here.  Think about this:
Natural selection can in principle be
either deterministic, because it moves traits in some direction over time
or probabilistic, because its direction inherently wavers over time
or both deterministic and probabilistic, because a trait can change in a given ‘direction’ over time yet
    not in a straight projection,
or neither deterministic and probabilistic, because a trait doesn’t change in a straight line nor does it just
    change purely randomly.  
As we'll discuss in the next po, one can always see after-the-fact then-to-now evolutionary change and argue that it was somehow determined and inevitable, in a force-like way.  Alternatively, one can argue that it's at least largely luck where things have got to where they are today.  Or, one can say it was deterministic at any given time but that the driving context changed over time.

The very same either-or-both-neither characteristics apply to the causal relationships between an organism's genotype and its traits.  Not all bearers of a given genotype have the same trait value, and a given environment doesn't seem always to have the same effect. Most genetic variants empirically, at as current studies are designed, have small or unstable effects relative to each other; the exceptions are often lethal.  That in turn means that natural selection cannot be a deterministic screen--it can't 'see' each individual's genotype.

We as yet have nothing close to a precise general theory for how deterministic these factors could be, or if not deterministic what causes them to be probabilistic, or if probabilistic what the determines the probability values.  Even in the latter case, we're usually stuck with very limited sampling and observation, not strong theory.

One deep but simple truth might be that DNA is basically an inert molecule that has no function until it interacts with (a physicist might say is 'measured by') its environmental context, however that itself is determined.  Genes and environment are not as simply separable as their separate names indicate.

We should take what we know about what we don't know seriously and make more of an effort to understand it.  Ignorance the the proper driver of science, but only if we acknowledge it.

In the end
Dogma is not helpful here.  Even to acknowledge that natural selection is a mix of determinism and probabilism is a rather empty tautology.  What sort of 'mix'?  Are there general laws that can tell us?  Causation, determinism, probability, uncertainty: are in themselves elusive concepts.

Most scientists acknowledge these facts when they’re pointed out, even if grudgingly when a vested point of view is threatened by that acknowledgment. While the facts we know may require that we gain a deeper insight into what determinism and probabilism actually may mean here, declarations of what is the primary mover are simply not very helpful.

All of this should temper the fervor with which stances are taken on this subject. Opening the door of complexity threatens ideological stances, in science and more acutely when applied to human life and society, but it's the only way to try to gain a deeper understanding, even if once the door is open you can't control the uncertainties that come pouring in.

The drug that reinforces staunch positions are those clear-cut conditions that we do know of, and this goes back to Mendel himself.  But even strongly causal individual alleles, even purportedly lethal alleles, demonstrably vary in their effects and sometimes have essentially no effects.  This is very clear from lots of data, including in humans where it is not just a politically-correct dream-world.  Neither environmentalists nor genomic determinists should shut the door on the nature of biological and evolutionary causation, including the important role of unpredictable chance.

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