Almost every post on this blog refers to biological functions and/or norms. It becomes repetitive to explain the entire theory behind these ideas in every post so in order to keep posts short and not bore readers who have read previous explanations I usually put a quick and fast thumbnail sketch and move on. This post is intended to be a place where I can put a summary of the theoretical background to keep from having to explain it afresh each time.
Nothing written here is an original idea of mine, it is a summary of the philosophical background material. There is a large literature in philosophy of biology dedicated to this topic. Specifically, I will explain the theory of philosopher Ruth Millikan first presented in her 1984 Language, Thought, And Other Biological Categories.
In biology it is common to say things like that the function of the heart is to pump blood, the function of a mating display to attract mates, the function of a danger signal to alert others to the presence of a predator, the function of camouflage to make one invisible to predators, and so on. Hearts do lots of things besides pump blood: they make a “lub-dub” sound, they freeze when put in liquid nitrogen, squish when stepped on, etc. Of all the things hearts do what is special about pumping blood?
Intuitively, the reason pumping blood is special to hearts is because hearts were selected by natural selection for their ability to pump blood, not do those other things. This approach of using selection to understand function was pioneered by Wright (1973), but it was Millikan who opened the floodgates of interest in functions because Millikan revived interest in how the application of a theory of function could do serious work in addressing philosophical disputes.
In the philosophical literature, the effect that an item produces that causes it to be selected for reproduction is called its etiological function, or teleofunction, or proper function. According to Millikan, to have a proper function is not a matter of possessing a certain property or set of properties, but the possession of a certain history: there must be a history of 1. selection resulting in 2. reproduction or copying in order for an item to be considered to be in the possession of a function. A feature of an item is a reproduction in this sense if the presence of that feature is the result of the workings of natural law such that had a previous item (the ancestor) been different in that respect the other item (the descendant) would differ accordingly. Picture the way the color patterns of a chameleon’s skin match the surface upon which it sits. If the surface had been a different color, the chameleon’s skin would differ accordingly (assuming the chameleon’s pigment arrangers are working as designed). Further examples are the way that the characters on the paper that come out of a photocopier correspond in shape to the characters that are on the originals, or the way that children’s genes are copies of their parents’ genes.
The selection requirement for the possession of a function is the Darwinian process by which an item or feature is passed on because it has sufficiently often produced some effect that has contributed to the item’s successful reproduction as opposed to items lacking this feature. Those properties that are reproduced because in the past their ancestors have had a certain effect which lead to successful reproduction are called the reproductively established character of the item, and the effect in question is the function of the item.
And so in short, to understand an item’s proper function is to understand that which its ancestors did that accounts for the item’s reproduction as opposed to items lacking that feature. In the case of biological items such as organs or inherited behaviors such as mating displays, the function is that effect an item’s ancestors had that accounted for the proliferation of the genes responsible for its production. One’s genes are copies of one’s parents’ genes, and the genes that produce hearts have been selected by natural selection because they produce hearts. Hearts themselves contribute to the increased likelihood that an individual’s genes will be passed on due to that fact that they pump blood, not because they make “lub-dub” sounds, or squish when they are stepped on, or freeze when put into liquid nitrogen, or any of a million other things.
Items other than genes and their biological products may have proper functions as the theory merely requires that the reproductively established character to have been selected for reproduction because it has correlated with some effect more positively than items lacking this feature. Millikan, for example, claims that the imperative and indicative linguistic moods possess the functions to produce behavior and to produce true beliefs respectively (see LTOBC: ch. 3). Likewise, a learned behavior can have a function if it is reproduced because it has led to a reward; it being the function of the behavior to bring about this result, and a manufactured good such as a screwdriver can have turning screws as its function since it is this ability that has lead to the selection and reproduction of screwdrivers in manufacturing. It was its ability of previous hammers to drive nails by possessing some particular shape and hardness that caused this hammer get its shape and hardness through our copying these features in manufacture. The possession of a proper function is a purely natural fact of the matter as to whether an item possesses such a history, it is not a matter of human interests, practices, or conventions.
For each item that possesses a function in the sense described here there will be an explanation of how the item has historically managed to perform this function. This explanation will mention how the structure of the item in question has managed to “do its job” historically, what conditions were in effect, what the environment was like that allowed the item to successfully perform it function. Millikan calls such an explanation a “Normal” explanation and the conditions that have historically held in order for the item to succeed in performing its function “Normal” conditions (1984: 33). “Normal” is capitalized to prevent confusion that might occur if one was to think that Normal conditions are average or frequent since “normal” often has that connotation. Millikan’s “Normal” is a technical term with this specific meaning. For example, just think of how few sperm manage to perform their function of fertilizing an egg, or how infrequently the skull needs to perform its function of protecting the brain from impacts. It might be helpful to think of Normal conditions as “activation conditions” or “enabling conditions.” In abNormal conditions an item will fail to perform its function, or at least fail to accomplish it in accordance with a Normal explanation. Diseased hearts are in abNormal conditions, being underwater for extended periods is an abNormal condition for otherwise healthy lungs, and whatever it is that prevents a specific sperm from fertilizing an egg is also an abNormal condition.
And so as an intuitive shorthand we can think of “biologically normal” or Normal (for short) as working as designed by natural selection, or being in the condition it is supposed to be in, where “design” and “supposed to” means that the item is in the condition its ancestors were in on those occasions where they actually were selected for by natural selection.
For instance, take the nectar retrieval system of the honeybee. When a bee finds a source of nectar it flies back to the hive and does a squiggle dance. The turns and pace of the dance indicate to watching bees the location of the nectar relative to the sun and hive. The perceiving bees then fly off to the location indicated by the dance and retrieve the nectar. That is how the retrieval system is supposed to work, how it is designed to work. Lots can go wrong however. For one, perhaps the bee misidentifies something as a source of nectar that isn’t one. Maybe it is a plastic flower and not a real one. Or perhaps this bee has a brain parasite and its internal mapping system miscalculates the location of the nectar. Or perhaps the system that translates the bee’s inner directions into dance moves suffers from brain damage so that the bee does a malformed dance. Or perhaps the viewing bees have visual impairment and perceive the dance incorrectly and so fly off in the wrong direction. Or maybe environmental conditions are unfavorable and the bees are blown off course by a tornado. All of these are abnormalities that prevent the dance from performing its function as it was designed to. But none of this shows that the dance wasn’t supposed to map the location of nectar, or that a sperm which doesn’t fertilize an egg wasn’t supposed to, or a heart that can’t pump blood wasn’t supposed to, or camouflage that fails to make an animal invisible to predators wasn’t supposed to. This is how it can be said that camouflage might fail, or that a heart might be deformed, or that there is a right dance for the bee to do given the location of nectar, or that a thalidomide baby developed abNormally.
Teleological functions and Norms have some interesting characteristics.
A) Human intentions do not determine an object’s function. One may intend to use a toaster as a door jam, or a space heater, or to illuminate a room by the glow of its electric coils, but none of these things are its function (what Millikan calls a direct proper function). These uses are what Millikan would call “derived” proper functions; the sense in which we would say that the toaster is functioning as a heater is derived from the user’s intentions (Language, Thought, and Other Biological Categories, ch. 2). Prototypes of artifacts have only derived functions, when they begin to be replicated because they produce some effect they acquire a direct function as well.
B) An item may be able to perform its function only if external conditions are right, and yet because conditions are never right, the item may never perform its function. Millikan gives as an example an ice-cream machine. In order for an otherwise working ice-cream machine to perform its function, it needs to be hooked up to the appropriate environment and receive the appropriate ingredients as inputs. But because in this example the environment is never right and this particular ice-cream machine is never actually loaded with the correct ingredients, or plugged in and turned on, it never performs its function. And yet making ice cream remains its function (see “Existence Proof for a Viable Externalism,” The Externalist Challenge. New Studies on Cognition and Intentionality, p. 230).
C) An item with a teleofunction may be physically unable to perform it. A diseased heart may be unable to pump blood, yet that remains its function. It is because the possession of a teleofunction is a matter of what one’s ancestors did that the current item may lack these features and yet still have the performance of that action as its function.
D) The possession of a function is an objective fact. It is not a matter of opinion, or interpretation, or a matter of social agreement. It is a fact that the function of the heart is to pump blood. Anyone thinking otherwise is factually wrong. Aristotle thought that the function of the brain was to cool the blood; his proposition to that effect was false. Indeed, generations of biologists may be in agreement as to the function of some mechanism, and yet be wrong about it.
E) An item may fail in the performance of its function more often that it actually achieves it. For example, certain animal mating dances might fail more often than they succeed, yet they succeed often enough to make it worthwhile to keep them in use.
F) Saying that an item has a function is not to provide a conceptual analysis of the concept of that item. In describing an item’s function one is not giving a list of necessary and sufficient conditions for being that thing; having a function is neither necessary nor sufficient for producing the effect in question. Being a heart is a matter of possessing a certain history, and this history can not be revealed by conceptual analysis. In addition to possessing this history, in order to perform a function conditions must be what Millikan calls Normal conditions (LTOBC, p. 33). Even pumping blood can be missing from a heart, as is the case in deceased, diseased, or damaged hearts, and yet pumping blood remains the heart’s function.
Darwinian Reactionary 