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Do We Need Purposes in Biology?

Emily Dickinson often had a rather chilly view of things. Around the end of the Civil War, five years after Charles Darwin had published his Origin of Species, she wrote this short poem about the life of worms:

Our little Kinsmen—after Rain
In plenty may be seen,
A Pink and Pulpy multitude
The tepid Ground upon

A needless life, it seemed to me
Until a little Bird
As to a Hospitality
Advanced and breakfasted.

As I of He, so God of Me
I pondered, may have judged,
And left the little Angle Worm
With Modesties enlarged.

Notice how, right at the beginning, the poet identifies us humans with worms. Things only go downhill from there! The worms are gobbled down by a bird, and much the same seems to be said of our relationship with God. I doubt the suggestion is that God likes a good human flank steak. Instead, the point is this: As we see the worm has a purpose, so God sees that we have a purpose; but just as the purpose of the worm has no connection to the worm’s wellbeing, so our purpose seems not to have much to do with our wellbeing.

Now, I don’t want to go into a detailed discussion of the full meaning of the poem. (What does Dickinson intend by “modesties enlarged,” for instance? Does that give us a break?) Rather, I want to pick up on the structure of Dickinson’s reasoning. The worm’s existence has meaning when we see that it exists in order to be food for the bird. The same for us with God. The purpose of the worm — its end — is to feed the bird. Our purpose, our end, comes from God’s needs. (That is what makes the poem chilly, because we often think God focuses on our needs.) Notice what is going on: Normally, when we consider the way things in nature exist and are connected with other things, we think in terms of what philosophers call “efficient causes.” The bird is hungry; it sees a worm; various physiological processes kick in and the next moment the worm is on the breakfast menu. Dickinson isn’t quite thinking this way. She is putting the worm before the bird, one might say. Why does the worm exist? In order to feed the bird. That is the worm’s purpose.

Leave aside whether biologists would agree with Dickinson’s reasoning here. I want to point out that we seem to have a reversal from what happens in the case of efficient causes. Instead of hunger explaining why the bird feeds, the nature of the worm explains why the bird acts to satisfy its hunger. In other words, instead of having the hunger cause the feeding, we have the bird’s behavior being explained — i.e., caused — by the worm. The order of explanation is reversed: not causal event (hunger) to future effect (feeding), but future goal or purpose (feeding) to past phenomena (hunger). This is what is known as “final causation” or teleology.

But what happens if a cat suddenly jumps in and kills and eats the bird? Clearly, the bird would not be able to eat the worm, and so the worm’s purpose — or telos — would not be realized. Here’s the rub: in the case of teleological causation, there is no guarantee the goal will be attained. You cannot say that if there is a worm there necessarily will be feeding, even though the worm exists in order to feed the bird; only time will tell. From the modern scientific perspective, this may not seem like a very satisfactory type of explanation. We want to be able to predict with accuracy what will happen, not what tends to happen but very well may not.

Such problems involving causation have occupied thinkers at least since the ancient Greeks. Beginning with modern science, “final causes” have proved particularly controversial. Some scientists and philosophers have suggested we just stop thinking and speaking this way and stay with efficient causes. In fact, already in the time of the ancient philosophers, the atomist Democritus expressed such a view. Several centuries later, his follower, the Roman poet Lucretius, wrote scathingly of final causes that,

… explanations of this type …

are back to front, due to distorted reasoning

… all the things which were first

actually engendered, and gave rise to the preconception of

their usefulness later.

Primary in this class are, we can see, the senses and the limbs.

Hence, I repeat, there is no way you can believe

that they were created for their function of utility.

But dropping final causes may be easier said than done. In the world of evolutionary biology, in particular, there is still a huge amount of final-cause thinking, despite the fact that Darwin is often said to have done away with teleology. Why does the stegosaurus have diamond-like plates running down its back? In order to control body temperature, cooling in the heat and catching sun in the cold (no small issue for a cold-blooded organism). The plates exist (or rather used to exist) in order to — for the purpose of — controlling the temperature. You don’t get this kind of thinking in the physical sciences. In physics, objects don’t have any purposes; we don’t need to appeal to the final goal or purpose of the moon, for instance, in order to explain it. (If the sardonic suggestion is made that the moon exists in order to light the way home for drunken philosophers, you know that is a joke.) But if physics can do without final causes, why can’t biology?

The worries about final-cause thinking increase when one looks at some of the purposes to which it gets put. Are final causes the thin end of a wedge that, when driven in, gets us into religion, perhaps even the Christian religion? You think you are doing paleontology, unearthing the characteristics of animals and plants, but truly you are in the God business, revealing His ultimate designs. Plato and Aristotle lived centuries before Christ, but their views about final causality came to influence later Christian (as well as other religious) thinkers.

Plato suggested that the key to purpose-like thinking is that the world was designed by an intelligent being — something that in the Timaeus he called the “Demiurge.” Aristotle believed in an ultimate deity, the Unmoved Mover, but had no sense that this being did any designing. Indeed, He (or She or It) seems almost oblivious to earthly existence, as it contemplates its own perfection. But, in some sense, Aristotle thought there must be some kind of drive or force directing everything in nature toward their intrinsic ends. Ultimately, he thought this drive could be explained by a natural impulse to draw nearer to the Unmoved Mover. Whether this tendency in things is construed as something actual — a kind of occult force — or a principle of ordering, we have goal-directed activity. I wouldn’t say that this forces the Christian God on you, but the natural world of Plato and Aristotle is a lot more spirit-infused than it is under the Cartesian philosophy, where matter is just lifeless extension — res extensa.

As a matter of fact, this type of final-cause thinking was the basis of the so-called argument from design, used by Catholics like Thomas Aquinas and Protestants like Archdeacon William Paley to demonstrate the existence of God. Paley famously used the analogy of the watch. Why does a watch have a short arm and a long arm? Because someone designed it that way so that it could tell us about hours and minutes, The arms exist for the purpose of telling the time. By analogy, the stegosaurus has those plates because the Great Zoologist designed them to be the way they are in order to control heat.

I don’t want to say that final causes — whether understood as external teleology (as in Plato) or internal teleology (as in Aristotle) — are silly or useless. However, such thinking does run into philosophical problems, especially when put to work proving the existence of God. The philosopher David Hume pointed out that there are all sorts of things that call for final-cause thinking, and which nevertheless seem to point not to a perfect designer, but to a rather nasty one. As Darwin worried, what about the adaptations of parasites that cause so much discomfort to the hosts? In Emily Dickinson’s poem, however “enlarged” its “modesties,” the worm doesn’t fare so well. At the very least, how do we know that the designer in question is the singular all perfect creator-being revealed in the Abrahamic religions and not, say, a committee of super-designers? Is the analogy between the universe and a watch even plausible to begin with? As for internal forces, what is the empirical evidence for them? Are they spirit clouds hovering over everything in nature rather like the fog over the meer in the Sherlock Holmes novel The Hound of the Baskervilles? If so, why should modern science care?

Breaking with tradition, Immanuel Kant argued in the eighteenth century that final-cause thinking is essentially heuristic: final causes don’t exist out there in nature, but are instead something we impose on nature to make sense of things. We may appeal to purpose or function of temperature control when interpreting the stegosaurus plates, but that doesn’t mean that these purposes actually subsist outside our minds. Maybe Kant was on to something. But where he fell short was not explaining why final-cause thinking is appropriate and even necessary in the case of biology — to explain organisms, for instance — and not physics. Why can we talk of the purpose of the stegosaur fins but not of the moon? Kant was not like Democritus or Lucretius, sneering at the use of final causes, though he did agree with these ancients that such causes lack objective existence. In the end, Kant gave up, declaring that “it is absurd … to hope that another Newton will arise in the future, who shall make comprehensible by us the production of a blade of grass.” One suspects that Kant really thought that God was behind it all, but his philosophy forbade him introducing God into these kinds of discussions in an explanatory way. One also suspects that Kant’s Pietist background, with its stress of faith over reason, may be important here.

Charles Darwin added the missing piece. His mechanism of natural selection didn’t just introduce change into the biological picture. It introduced change of a particular kind, namely natural processes that produce features that look design-like. In the Darwinian account, if natural features, such as the stegosaurus’s plates, weren’t design-like, they wouldn’t help their possessors survive and so they would lose out in the “struggle for existence.” Contrary to popular representations, Darwinian change is not higgledy-piggledy but orderly (if not designed). As Darwin himself puts it:

How have all those exquisite adaptations of one part of the organisation to another part, and to the conditions of life, and of one distinct organic being to another being, been perfected? We see these beautiful co-adaptations most plainly in the woodpecker and mistletoe; and only a little less plainly in the humblest parasite which clings to the hairs of a quadruped or feathers of a bird; in the structure of the beetle which dives through the water; in the plumed seed which is wafted by the gentlest breeze; in short, we see beautiful adaptations everywhere and in every part of the organic world.

The answer is natural selection. So here we have the reason why final-cause talk is permissible and necessary. Thanks to the processes of evolution, organisms appear design-like, even though they are ultimately the result of random variations plus natural selection. In order to make sense of this fact, we often think and talk in terms of ends or purposes, although these ends or purposes don’t actually exist in the real world. So in a sense, Kant was right: teleological thinking is heuristic, something imposed on the world by us. It is no less useful or legitimate for all of that. Physics doesn’t have need of final-cause talk because, not having been produced by natural selection, the objects of physics do not appear designed in the same way.

While this takes God or occult forces out of the scientific picture, don’t think that going this direction means that all is secular or meaningless — Kant and Darwin today, Richard Dawkins tomorrow. Far from it! The believer can continue to see nature as God’s creation and natural processes as God working His purposes out. It is just that God does it through evolution, rather than by intervening miracle. Moreover, something that remains important for both the believer and the non-believer is whether final-cause thinking (understood heuristically) applies not only to the natural world but also to the human context. Can we treat human reasons as final causes?

I have my opinions on this but now is not the time for them. Suffice it to say that, thanks to Darwinian biology, we have a good solution to a major problem in the history of philosophy, but like all good solutions it opens up new questions and challenges. That is what makes it all so very worthwhile to be a human being and why I, for one, much as I love Emily Dickinson’s poetry, am not about to buy into her rather gloomy and cynical view of our place here on earth.