Even the most genuine and pure tradition does not persist because of the inertia of what once existed. It needs to be affirmed, embraced, cultivated. . . . Even where life changes violently, as in ages of revolution, far more of the old is preserved in the supposed transformation of everything than anyone knows, and it combines with the new to create a new value.
—Hans-Georg Gadamer (1992)
An interlude (Latin inter “between,” ludus “play”) was a short performance between the acts of a long morality play. The previous chapter addressed the origin of purposeful beings whereas the next chapter will address how purposeful beings make sense of their world. This interlude marks a transition from a focus on differences that make a difference in diachronic (evolutionary) time to differences that make a difference in synchronic (behavioral) time.
Recall Darwin’s thought experiment of old springs, wheels, and pulleys that have been employed in a series of different contrivances. What is the function of a pulley? One story might pronounce that the pulley’s real function is the role it performed in the first contrivance of which it formed a part. Another story might declare that the pulley’s functions are the roles it has performed in each of the successive devices in which it has been employed and that its current function is the role in which it is currently employed. Yet another story might aver that the functions of pulleys are the causal role they play in changing the direction of a force independent of the purposes for which any particular pulley is employed. What sayest thou?
Natural selection has two aspects that have been labeled positive selection (associated with origin of novel function and elimination of the old) and negative selection (associated with maintenance of existing function and elimination of the new). Under positive selection, old less-adapted gene sequences are replaced by new more-adapted sequences. Under negative selection, new less-adapted sequences are continually eliminated, soon after they arise, preserving old more-adapted sequences. Bouts of positive selection are invariably accompanied by a background of new deleterious mutations that are eliminated by negative selection. Old sequences now maintained by negative selection were once new variants favored by positive selection. Genetic differences make a difference in fitness under both positive and negative selection. The genetic sequences we see are the survivors of both kinds of selection.
Many differences of opinion in evolutionary theory hinge on whether negative selection is included or excluded as a component of adaptation by natural selection. Adaptationists and structuralists agree that conserved morphological and genomic features are maintained by negative selection. They agree that the gene regulatory networks responsible for developmental constraints are conserved, not because mutations do not occur, but because mutations are not tolerated. The problem is that adaptationists consider these to be functional constraints because they include both positive and negative selection under adaptation by natural selection, whereas structuralists consider them to be structural constraints because they exclude negative selection from adaptation. These semantic differences have been a recipe for mutual misunderstanding. As a consequence, adaptationists interpret the maintenance of structure in the face of mutation as an expression of the power of natural selection, whereas structuralists interpret the absence of positive selection as evidence of a constraint on what can evolve.
A definitional restriction of adaptation to positive selection is often accompanied by claims that a feature is only an adaptation for the “original” function for which it evolved by positive selection but not for any of the subsequent uses in which it is employed, even though performance of these new roles is maintained by negative selection. Thus, Stephen Jay Gould and Elisabeth Vrba (1982, 6) defined an adaptation “as any feature that promotes fitness and was built by selection for its current role. . . . The operation of an adaptation is its function.” They further proposed that “characters, evolved for other usages (or for no function at all), and later ‘coopted’ for their current role, be called exaptations” and that “the operation of a useful character not built by selection for its current role [is] an effect.” Exaptation has been a very successful meme, but what if most features of organisms are modified versions of earlier features that once performed other roles? This would mean that there are almost no real adaptations and very few functions but mostly exaptations and their effects. Not only would adaptation fail to signify many interesting features, but this terminology would fail to distinguish between those effects of an exaptation that were beneficial and those that were detrimental or neutral.
The search for the “original” function of a conserved feature resembles the search for the “original” meaning of a folktale that has been retold many times and has meant many things to different listeners and different storytellers. There may indeed have been an original telling that was not a retelling of yet older tales—and recovery of this original sense would undoubtedly be of antiquarian interest—but the existence of an original sense should not belittle the subsequent senses in which the tale has been told and interpreted. Another example will drive home this point. A word may have an “original” meaning that is listed as obsolete in the Oxford English Dictionary and derived meanings that are currently in use. A pedant might insist that only the earliest definition is the “true” meaning and all subsequent usages are simply exaptations of this original sense; but the reason why the word is currently used is its role in the language as understood by contemporary speakers. Meaning is synchronic use.
A still-current sense of dower is “the portion of a deceased husband’s estate which the law allows to his widow for her life,” and this was also the “original” (now obsolete) sense of dowry. Dower and dowry appear to have been minor variants of the “same” word derived from Old French douaire, but a dowry is now “the money or property the wife brings her husband.” Dower and dowry are currently understood to be “different” words. How did an obligation of the husband to the wife become a payment from the bride to the bridegroom? I do not know the answer to this question but can offer a just-so story to be tested against the historical evidence. In far-off days, O Best Beloved, dower was promised by the husband to provide for the wife in the event of his death. Highly desirable husbands then asked in their marriage settlements that the bride’s family endow the property that would constitute the dower if the husband predeceased the wife. Henceforward, what had been an obligation of the husband for support of the wife became a payment to the husband for taking the wife.
The essential oils of Ocimum basilicum (basil) are insecticidal compounds that evolved as a defense against insects. Human foragers would have moved through the woods nibbling the tip of a leaf here, and another tip there, and harvesting those plants that appealed to their palate. Palatable plants were therefore less likely to set seed. Appeal to the human palate was a maladaptation, not a purpose of wild basil, but the situation reversed immediately when foragers started collecting seeds from flavorful and fragrant plants and cultivating them. Now flavor was the reason for being planted. Seeds from less palatable plants were less likely to be planted and less likely to be protected from insects by gardeners. Seeds from plants that tasted good were more likely to be preserved. Appeal to the human palate had become a reason for the existence of basil plants.
What is the function of the essential oils of domesticated basil? One possible answer would be that their function is protection against insects and that appeal to the human palate is not a function but a serendipitous side effect. Another possible answer is that their function was protection against insects but now is appeal to the human palate. A choice between these answers is not a matter of identifying the true function; rather the choice indicates what the answerer means by “function.” I prefer the second answer, but you are not wrong to choose the first; we simply mean different things by “function.” A third answer could be that the function of the essential oils is both protection and flavor because the insecticidal function did not disappear with cultivation: cooks prefer to harvest leaves without chunks bitten out by caterpillars.
My fable of wild and domesticated basil is a retelling of Daniel Dennett’s (1987, 290) allegory of the wandering two-bitser. This was a soft-drink vending machine that had been designed to accept US quarter-dollars and dispense bottles in response. The two-bitser was then transported to Panama where it was used to dispense bottles when customers inserted quarter-balboas. The two-bitser functioned well in this new task because quarter-balboas were struck by the US mint from the same blank as US quarter-dollars, and the machine could not distinguish between the two currencies. Dennett considered the two-bitser’s function was now to accept quarter-balboas even though it had been designed to accept quarter-dollars, just as the function of the essential oils of domestic basil is to appeal to the human palate even though the oils had evolved to deter insects. With respect to its current functions, the two-bitser would “malfunction” if it dispensed a bottle in response to a US quarter in Panama or to a lead slug that had been shaped to mimic a quarter-balboa (or any other counterfeit coin). Similarly, the “designs” of natural selection can malfunction because the environment has changed or because the adaptation enhances fitness in some but not all of its current environments.
The word “function” is used in different senses in different stories. During the twentieth century, “functional morphologists” developed a concept of function that was intended to exclude considerations of end-directedness. Their research program was strongly influenced by engineering with an emphasis on the mechanical properties of Darwin’s springs, wheels, and pulleys but only a peripheral interest in the specific uses for which the mechanical parts were employed. Theirs was a Baconian function shorn of Darwinian purpose. Walter Bock and Gerd von Wahlert (1965) exemplify this tradition. They championed a definition of function that did not invoke “any aspect of purpose, design, or end-directedness” (274). The function of a feature was “its action or how it works” and included “all physical and chemical properties arising from [the feature’s] form” (273). The heart’s functions included thumping sounds as well as the propulsion of blood. Form and function were seen as complementary aspects of physical features. In this formalism, the functions of a feature were simply all of its effects considered without regard for the biological role that the feature might serve. Thus, “the legs of a rabbit have the function of locomotion—either walking, hopping, or running—but the biological roles of the faculty may be to escape from a predator, to move toward a source of food, to move to a favorable habitat, to move about in search of a mate, and so forth” (279).
Ron Amundson and George Lauder (1994) defended a “causal role” concept of function that was “both non-historical and non-purposive in its applications” (466). They saw the goal of functional analysis as explaining “a capacity of a system by appealing to the capacities of the system’s component parts” (447). Functions were capacities of particular interest (not simply all physical and chemical properties of a feature). The thumping of the heart was a simple and uninteresting property. “Scientists choose capacities which they feel are worthy of functional analysis, and then try to devise accounts of how those capacities arise from interactions among (capacities) of component parts” (447). By such criteria of functional worth, “Functional anatomists typically choose to analyze integrated character complexes which have significant biological roles” (450). For example, an anatomist might analyze the crushing capacity of a piscine jaw, but “While the decision to analyze the jaw may have been motivated by a knowledge of its biological role (the fish eats snails), that knowledge plays no part in the analysis itself” (451). Considerations of biological purpose could be used to choose which capacities were worthy of analysis, but these considerations were excluded from the analysis itself. Amundson and Lauder were thus able to choose objects of study by intuitive criteria of value but avow that their causal-role functions were uncontaminated by teleology.
Robert Cummins similarly rejected the grounding of function by natural selection and recent utility:
While it is plausible to suppose that there was a first flight-enabling wing somewhere among the ancestors of today’s sparrows, those ancestors were not sparrows. . . . Similarly, somewhere in our ancestral lineage is to be found the first appearance of centralized blood circulation. But those ancestors were not even vertebrates. . . . It follows from these considerations that sparrow wings and human hearts were not selected because of their functions. Selection requires variation, and there was no variation in function in the structures in question, only variation in how well their functions were performed. (2002, 164–165)
But variation of function was not absent. Cummins ignores the ever-present background of mutational variation and negative selection. Mutation is an expression of the universal tendency to disorder. Negative selection maintains useful order. Some sparrow chicks hatch without functional wings. Some human embryos are conceived without hearts. Neither wingless chicks nor heartless embryos leave descendants because sparrow wings are needed for flight and human hearts are needed for the circulation of blood.
A complete history of everything that happened (the Laplacean how come?) is unattainable and unusable. A useful history needs to identify patterns of events of particular significance (the reasons why things are as they are). The evolving sequences of genes preserve a textual record of past differences that have made a difference. The previous chapter analogized this textual record with the Aristotelian notion of formal cause. The initial dissemination of fortuitous slips of the pen is the role of positive selection, but any repeatedly recopied text will accumulate errors if not corrected for sense (this is the role of negative selection). The chapter also provided a justification for ascribing purposes to the products of natural selection. Final causes (functions) were identified with the reasons why some textual variants have been favored over others. These reasons may change with time. One might give a different answer to why this variant has been favored over the last hundred generations or the last thousand generations, and a different answer for why it was favored a thousand years ago and a million years ago. That is the nature of historical explanation. The restriction of the laurels of function to the original reasons for positive selection ignores the importance of negative selection. A long history of negative selection is essential if any record is to survive of ancient positive selection.
The next chapter addresses the intentionality of designed or evolved automata that interact meaningfully with their world. It will propose that the meaning of information for an automaton be considered the automaton’s output in response to the informative input. Some automata are simple: the meaning for the two-bitser of the “coin” that is inserted into its inner mechanism is whether or not a bottle is dispensed. Other automata are highly sophisticated, even capable of arguing about the meaning of “meaning.” Dennett (1987, 387) compared organisms to highly sophisticated automata that derived their original intentionality from natural selection but acted autonomously in the world: “We, the reason-representers, the self-representers, are a late and specialized product. What this representation of our reasons gives us is foresight: the real-time anticipatory power that Mother Nature wholly lacks. . . . We may call our own intentionality real, but we must recognize that it is derived from the intentionality of natural selection, which is just as real—but just less easily discerned because of the vast difference in time scale and size.”