Why not suppose, then, that the same is true of the parts of natural organisms [i.e. that nature acts not for something, i.e. for some final cause, but of necessity]? On this view, it is of necessity that, for example, the front teeth grow sharp and well adapted for biting, and the back ones broad and useful for chewing food; this result was coincidental, not what they were there for. The same will be true of all the other parts that seem to be for something. On this view, then, whenever all the parts come about coincidentally as though they were for something, these animals survived, since their constitution, though coming about by chance, made them suitable . Other animals, however, were differently constituted and so were destroyed; indeed they are still being destroyed, as Empedocles says of the man-headed calves. (Physics II.8, 198b23-33).
What we have here is an articulation of the evolution of species by natural selection. Say some animals have some parts well-adapted ("proper") for biting - sharp teeth. These sharp teeth are not there because that's what they are for, but rather coincidentally. What happens is that these parts get there coincidentally (a modern biologists would say this is "random variation"), and the organisms who had these adaptations would survive, while the one's who do not (like Empedocles' man-headed calves) would not.
This folks, is natural selection in essence. Let's compare it to Darwin's definition:
Can it, then, be thought improbable, seeing that variations useful to man [in the breeding of animals] have undoubtably occurred, that other variations useful in some way to each being in the great and complex battles of life, should occur in the course of many successive generations. If such do occur, can we doubt (remember that many more individuals are born than can possibly survive) that individuals having any advantage, however slight, over others, would have the best chance of surviving and of procreating its kind? On the other hand, we may feel sure that any variation in the least degree injurious would be rigidly destroyed. This preservation of favourable individual differences and variations, and the destruction of those which are injurious, I have called Natural Selection, or the Survival of the Fittest. (Origin, 107)
Now of course Darwin knew of this Aristotle passage - he quotes it in a footnote on the first page of the second edition - but he didn't think Aristotle understood its significance. The significance, from this passage, is that variation can and does occur, and the principle of "selection" of which variations will be reproduced and what will not is their fittest for survival. Aristotle obviously says the same thing, but with a big difference: Aristotle didn't think chance would work like this.
In fact, Aristotle rejects this argument precisely that because we speak of "chance" as something hardly ever taking place, while teeth are "normally" or usually there. In other words, animals having teeth is a very normal occurrence. If it is normal, then it is the very opposite of coincidentally or by chance, which by definition is abnormal. Thus we need to look at another cause. For Aristotle this is the "final" cause, i.e. that an animal needs this or that part to become a fully mature animal.
Now, I can imagine Stephen Jay Gould's response to this: if you want to get on board with Darwin, you need to expand how you think about "chance" to include lots and lots of time (thousands, millions, of years), and lots and lots of interactions at the genetic level. If you look at chance events over millions of years, instead of just a couple, or a few hundred, you can imagine how chance variations can come up, and while they seem like chance variations from a certain perspective, they take on a statistical regularity over the long haul. This "regularity" is enough, if looked at in the right perspective, for natural selection by random variation to make sense. Aristotle of course did not entertain this perspective (the reasons for this are not merely historical, but also philosophical). How could you, Aristotle might say, when by definition chance is not something that is regular? Chance by necessity is rare! But then again, as Daniel Dennett says, perhaps this was a case where Aristotle mistook necessity for a lack of imagination.
So why oh why did it take over 2000 years, from Aristotle to Darwin, for humans to recognize this fact? Was it Aristotle's commitment to "final causes" in nature (an idea that, so far as I've read scientists reading it, is very little understood by most scientists today)? Was it an "essentialism" in Aristotle, Platonism, Islam, and Christianity, modes of thinking that dominated our culture for those thousands of years? Was it that Darwin finally let go the shackles of dogmatism that plagued everyone from Plato to Paley? This is the standard story, no doubt, biologists tell.
Yet I have an alternative hypothesis, something I have not done enough research on to really defend here. My hypothesis is this: in order to entertain random variation there had to be the historical development of population science. This historical develop only arose with the modern state and notions of managing large populations. The very idea of "population" is something almost completely foreign to Aristotle's time. When you ask a question about a species you ask the question about a typical example of the species, not about the "distribution of attributes across populations," which is what statistics like the birth rate and the death rate do. This only happens with the advent of the modern nation-state, where territory and population take on a completely different sense than it ever had, and where you understand the nation in terms of its population, rather than its ethnicity, or its king, etc.
One might retort - 'so what. So that's the development. It's no secret that science and ideas develop over time, and that there are antecedents to ideas. So population science was antecedent to Darwinian evolution. Big deal.' The big deal, however, is a question of perception. What type of perception goes into population studies? How has this perception altered our very everyday senses and perceptions of our world? Do we understand, on the whole, more or less about the world now that we see in "populations"? I don't mean expert scientists, but common people. If we are, presumably, "enlightened" individuals, "moderns" who are no longer bound by the shackles of dogma and religion (unless you happen to be one of those creationist fundamentalists), then we should actually know more about the world than people did, say, 300 years ago. But is the case?
I would say not. In fact, we're probably more ignorant of our world, as a general rule, than people were 300 years ago. Back when people actually engaged with things around them, instead of relying on technology or experts to give them all of their "knowledge" ("giving" here merely means: making things we use, without the slightest idea how they work). I would actually say, even if Aristotle is completely deficient in terms of "scientific" knowledge, he actually does give us something, in terms of common understanding, that really does help us know about our world.
Asking the question "why", for Aristotle, can be answered almost entirely by your senses. You can ask: "why does this bird build a nest like this"? If you look at the nest, you look at the four ways we speak of "cause": you can find the "material" cause, the "efficient" cause, the "formal" cause, and the "final" cause all with your eyes. Paradoxically, modern science actually takes your eyes out of the equation - and replaces it with an equation - algorithms for variation, models of bird behavior, etc. Your eyes are actually deceptive - 'you think this table looks solid? Well my friend, you must know that it is made up of billions of atoms, and most of the volume of an atom - that space between the electron and the nucleus is complete void, empty space. If it weren't for the electromagnetic force that attracts and repels, friends, we'd fall right through this floor!' This type of explanation, like an evolutionary one might be for a bird nest, is much more "accurate" than Aristotle's four ways of speaking about causes, but at the same time, for our normal interaction with the world, is almost useless.
Population studies, and most science today, are the sole purview of well-trained, well-funded, policy-arms of national governments. The "knowledge" of populations and the "management" of populations go hand in hand. Today, as Sajay Samuel says polemically, the polis or people are the subjects of experiment by the "experts." And this has been true since the beginning of population studies. Biology is not merely a way of seeing the world, but a way of making the world.
Now, I'm not saying we go back to Aristotle. What I am saying is that Aristotle's attitude - that we begin with our common sense, our common understanding, is essential. We as modern people have given up our knowledge to a science that has become so obscure that most people have almost no knowledge about their surroundings. Perhaps we need to re-think the value of this common sense?
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