Survival of the Fittest

 

 

Survival of the Fittest

 

What is it that survives and possesses fitness? The organism, of course: natural selection favors organisms that survive longer than other organisms—they are the ones with a greater chance of reproducing themselves. And the fitter the organism is the greater its chances of survival to reproductive maturity. Evolution is all about which organism can live the longest, i.e. can persist through time better than its rivals. Organisms are the focus of natural selection; they are the things that carry the genes over time, ensuring their survival. Clearly organisms persist over time—the point hardly needs stating—and this fact is key to the evolutionary process: persistence is what every organism strives to achieve, the better to pass on those precious genes. The ontology of the theory of evolution is thus an ontology of organisms existing over time. The theory quantifies over individual organisms and regards them as continuant particulars—substances, in the Aristotelian sense. And it is much concerned with whether these living substances live or die, reproduce or fail to, survive or perish, stay in existence or go out of existence. We are very concerned with that in our own case—we are the death-obsessed species—and evidently so is the process of natural selection: individual survival is the name of the game. How could this not be the case?

            But do organisms survive over time? Don’t caterpillars go out of existence to be replaced by butterflies? Is this contrary to the spirit of natural selection? Doesn’t natural selection seem to favor this plan? It is more adaptive to cease to exist than to continue to exist in the world of Lepidoptera. You might retort that actually the caterpillar still exists in the form of a butterfly, and so does not go out of existence—it survives the transformation—but do you want to commit evolutionary science to this metaphysical proposition? For that is what it is: it isn’t a theorem of biology or an empirically discovered biological fact. It’s a philosophical assumption. And it looks less plausible than the alternative, namely that the caterpillar does not survive metamorphosis and is replaced by a spanking new butterfly. But isn’t this just an extreme example of a biological commonplace, viz. biological change over time? Organisms don’t stay the same: they grow and mutate, often changing their form dramatically. The seed becomes an oak tree; the egg becomes a chicken; the sperm and ovum becomes a great scientist. Does it matter if we say that there is identity through time here? What difference would it make to evolutionary biology if we said instead that organisms don’t persist over time? Maybe selves do (or maybe not), but do we want to make biology hostage to metaphysical fortune? All biology really cares about is whether certain combinations of traits have the ability to survive, not whether some supposed underlying substance does. Can’t we just drop this way of talking and leave evolutionary biology intact? Then the ontology of persisting individual organisms will no longer be central (or even relevant) to biology; instead we will talk of bundles of traits and their adaptive capacity. We might call this Humean biology—biology without persisting substances.    [1] Natural selection works primarily on traits, or bundles thereof, not on individual organisms that allegedly bear these traits; and the traits persist only when they do, not when they are replaced by new traits in the ongoing life of the organism. We have an ontology of traits not an ontology of persisting substance-like organisms—characteristics (“characters” in an earlier terminology), properties, types, forms. Some of these traits work better than others in the bid to reproduce, but we don’t speak of particular organisms surviving or perishing; life and death cease to concern us as theoretical biologists. We drop the metaphysics of enduring substances and replace it with a metaphysics of characteristics—types not tokens. The question is not whether this or that individual organism will survive but whether this or that constellation of traits will survive. Traits are where the evolutionary action is. The dinosaurs are now extinct—there are no such individual organisms stalking the planet—but there are also no more dinosaur traits in the biosphere. Those traits proved not to be adaptive in the new world they confronted, so they disappeared. If by some miracle individual dinosaurs had transformed themselves into mammal-like creatures, thus surviving the drastic change of environmental conditions, the evolutionary situation would have remained essentially the same—no more dinosaur traits. It’s the traits that come and go by natural selection; the individual organisms that happen to bear them are neither here nor there. If organisms could survive their apparent death and continue down the generations, assuming different forms, that would make no difference to the evolutionary story: we would see the same pattern of trait exemplification and trait elimination that we see now. The theory itself is quite neutral on these metaphysical questions; it is concerned only with the explanation of the persistence of designs—plans, phenotypes, forms, and functional structures. The fittest of these survive, or fail to; the individual organisms are as may be. Even if there are no individual organisms—this is just misguided prescientific ontology—that is irrelevant to the truth of standard evolutionary biology. We could drop the whole idea of individual persistence and make do with an ontology of events and processes (as some have suggested for physics): there is nothing that survives from day to day but just an ever changing array of characteristics grouped together—as has often been supposed for the self. According to this conception, nothing ever survives over time in the biological world, so there is no such thing as survival of the fittest organism. But still some bunches of traits do better than others: they survive, but they are not persisting particulars–they are not living organisms.

            On this way of looking at things, organisms and their individual survival recede into the background, theoretically speaking, to be replaced by more general entities. We won’t any longer say dinosaurs are extinct; we will say their traits are. It doesn’t matter whether the individual animals somehow made it through the dust and darkness and now exist in the garb of birds; all that matters is that their phenotype went the way of the dodo’s phenotype (individual dodos might have survived in the form of platypuses). We humans are very concerned about matters of individual life and death, but from nature’s point of view that is an irrelevancy: organisms are simply bearers of traits, and traits are where the evolutionary action is. Evolution is essentially a process of trait generation and trait elimination: if there could be traits without organisms to possess them, the process would be essentially the same. So stop thinking of individual organisms coming and going and think instead of a vast sea of biological characteristics subject to forces of elimination. Animals only come and go in virtue of possessing these characteristics, so we may as well put the characteristics at center stage. Theoretically speaking, that is all there is: the individual is just a tiny pawn in a vast game of trait competition and differential survival. Alternatively, it is the traits of individual genes that are locked into the competitive battle not the individual genes themselves (types not tokens). Whether token genes persist through time is of no significance; what matters is that certain types of genes make it into the next generation. It doesn’t matter whether the gene tokens live or die; all that counts is that they give rise to copies of themselves that may be passed on, i.e. tokens of the same type. To put the point differently: nature doesn’t care about the individual and its survival; all it cares about is the general type exemplified by that individual. The usual way of putting things places the individual organism at the center of the story, but that is a human viewpoint not the viewpoint of impersonal nature.    [2]

            Think of it this way: human artifacts are also locked in a struggle for survival as a result of market forces, but the struggle is between designs not particular objects. It doesn’t matter whether your individual phone is a good survivor or even whether it exists over time; what matters is that certain designs are selected by the prevailing economic forces. The fittest phone design will persist into the future, because that’s what matters to market success. Similarly, the best mouse design will be the thing that persists in the future; the fate of individual mice is of no consequence. The mice are just carriers, temporary vehicles. This is why lifespan is biologically irrelevant: you might think that longer lived species have the advantage over shorter lived species, since after all the species members survive longer, but a moment’s reflection shows that this is wrong. The shorter-lived species prospers in proportion to its ability to propagate its traits; it doesn’t matter that individuals don’t last long. Long-lived species can easily go extinct if their traits are no longer adaptive. Turtles are not more adaptive than ants just because individual turtles live a long time; and the ant phenotype has been around forever. The fittest organism on the planet is not the one that has lived the longest (some tree somewhere) but the one that has the most viable phenotype with respect to reproductive success. In a slogan: it’s the phenotype, stupid. Individual persistence through time is not the important variable; frequency of traits is. Here insects and bacteria have the advantage over every other species. Or, to put it within the requisite theoretical perspective, being a quadruped (say) is a massively successful trait—as is having eyes and ears, a stomach and lungs, blood and bile. These traits are everywhere, existing across species; they are what have won out in the evolutionary lottery. Even the species as a biological entity pales in comparison with these highly general traits: they are the true units of natural selection, the building blocks of life. They don’t tend to go extinct simply because they are remarkably successful: they are the real survivors. But they are nothing like individual organisms, let alone sentient creatures; they don’t resemble human persons at all. Yet they are the things whose fitness leads to their survival; they are what nature really cares about. That is, they are what nature in all its uncaring indifference actually selects to enjoy the privilege of existence—organs, bodily shapes, biochemical processes, and efficient physiological mechanisms. These are the most prized products of natural selection at the basic level.    

[1] I am thinking of so-called Humean views of personal identity, according to which there is no continuing substance constituting the self but just a succession of connected psychological characteristics. It is easy to apply this conception to organisms: they are just series of linked characteristics not continuing underlying substances. We thus arrive at eliminative views of both the self and the organism. Such views, whether right or wrong, should not be incompatible with either psychology or biology as theoretical sciences.    

    [2] There is also a bias in favor of the particular: we like to think that reality revolves around particular things, since they constitute our perceptual world. We shy away from abstractions (hence the desire to think of laws of nature as somehow made up of particulars). Accordingly, we place particular organisms at the center of our theories of the biological world. But we do better to see that the important generalizations apply at the level of types, i.e. traits of organisms. Much the same is true of physics: the physicist is not greatly concerned with the fate of particular particles, or even particular galaxies, but with such abstractions as gravity, electricity, motion, mass, etc. In other words, biology needs to step back from the perceptible particular in framing its theories.

 

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