by Gene Callahan
Mario called into doubt the usefulness of purposive explanations in biology in this thread. I started to write up the following as a comment, but it grew long enough, and, I hope, of enough general interest, that I found it appropriate to elevate it to “post level.”
I think the evidence is very strong that biologists just have not been able to do without thinking of the “purposes” of biological features, despite the scientistic prejudice against regarding any such consideration as scientific. (Note: The previous and all future scare quotes in this post are introduced to indicate the disputed and possibly merely metaphorical usage of the terms in scare quotes, so that I am not guilty of petitio principii.) For instance, the semiotician Thomas Sebeok has noted the many ways in which semiotic analysis has enhanced biological understanding, and has concluded that the primary characteristic of life is that living things engage in semiosis. For example, single-celled organisms “interpret” a chemical gradient, with “memories” lasting up to a few seconds, so as to direct their movement away from toxins and towards nutrients. Similarly, in more complex creatures, the immune system “interprets” objects it encounters so as to classify them into “self” and “non-self,” in the interest of attacking the “non-self” entities.
These interpretive schemes imply purposes: in the first case, to avoid toxins and find food, and in the second to destroy harmful invaders. Indeed, I find it hard to imagine how biologists could even identify something called an immune system without the idea of “that part of an organism that has the purpose of destroying foreign invaders.” And how in the world would ethologists begin to understand, or even to recognize as separate from all other wolf behaviour, the way a wolf pack coordinates its hunting activities, except by recognizing that these activities have the “purpose” of catching prey? Or consider the “bee dance.” It was a major breakthrough in understanding what was going on with this activity (which had been recognized as early as Aristotle) when Karl Von Frisch realized that this dance had the “purpose” of directing other bees to good sources of nectar.
Mario writes: “If a evolutionary biologist says something like ‘the animal’s long neck has the function of helping it get food from high trees,’ there is no implication that it might not also have another function.” Secondary functions of biological features no doubt exist. Indeed, as we have seen, Aquinas assigns to human sexuality three different functions. But does anyone really doubt that eyes evolved “in order to” yield to their bearers increased information about their environment from the electro-magnetic spectrum, even if, as a secondary feature, when I bat my baby blues all the ladies swoon? (Well, OK, perhaps only my wife swoons.)
I don’t regard any of the examples presented above as being anywhere near conclusive evidence that biological theorizing inherently incorporates the notion of purpose. Perhaps some ideal, future biological science will indeed do without teleology. But the fact that most biologists, for more than a century, have pledged their allegiance, at least when directly addressing the matter, to the scientistic goal of banishing teleological thinking from their theories, and yet biology is still suffused with such heretical explanations, to the extent that even a religious materialist such as Richard Dawkins cannot help but assigning to genes the “purpose” of replicating themselves, should at least make us give serious consideration to the idea that intentionality is a perfectly valid, perhaps indispensable, part of biological science.