Friday, July 8, 2016
Aristotle Saves Biology
I confess that I did not know, until tonight, that Aristotle understood precisely what a lunar eclipse is. This is rather significant, because I had generally assumed that Aristotle’s physics was entirely indefensible. While I am now on solid ground in holding that is biology is mostly solid ground, what of his view that a pitched falls back to earth because its earthy nature compels it to return to its natural place? Aristotle did not have a reliable theory of momentum. But then I came across this passage in the Posterior Analytics.
τί ἐστιν ἔκλειψις; στέρησις φωτὸς ἀπὸ σελήνης ὐπὸ γῆς ἀντιφραξεως.
Pretty straight forward, no? Here it is in English.
What is an eclipse? A deprivation of light against the moon due to the obstruction of the earth.
That is dead spot on, which is astonishing for his time. He even goes on to say that this explanation, which relies on speculation, would be directly apparent if we were standing on the moon. We would see the earth moving across the sun. I am not going to try to rehabilitate Aristotle’s astronomy; however, I can’t help pointing out that, in considering the same event from two different points in space, he is perilously close here not only to Newton but to Einstein.
I was reading the PA because I read a very fine paper by Lucas Mix: “Nested explanations in Aristotle and Mayr,” in Synthese (2016) 193: 1817-1832, and Mariska Leunissen’s book Explanation and Teleology in Aristotle’s Science of Nature. Leunissen points out that Aristotle’s explanatory strategies may help us resolve certain fundamental problems in the modern philosophy of biology. This is what Mix tries to do in joining Aristotle with Ernst Mayr, two of my favorite philosophers of biology.
Modern biology involves a host of evolutionary and organismal explanations that cannot be generated by physics and chemistry alone. Chemistry can tell you a lot about the DNA molecules but it cannot explain what a gene is, let alone make sense of organisms, adaptation, end-directed processes, etc. At the same time, all biological phenomena depend on the mechanical laws of physics. All organic activities, from metabolism to mental gymnastics require the expenditure of energy and fail when the energy runs out; yet only organisms can succeed or fail at anything. How are we to understand the relationship between these two domains of science?
Here is how Mix puts it:
Nested explanations provide the most utility for biology. Good evolutionary explanations involve natural selection acting on replicating physical systems; therefore, the fullest biological knowledge will appeal to an evolutionary explanation nested within a mechanical explanation (or series of explanations). The evolutionary explanation is etiologically prior; it defines the categories in question (functions, organisms, genes). The mechanical explanation is temporally prior; it includes the material from which they are made and the rules by which they interact.
To say that evolutionary explanations are nested with mechanical explanations is to say they are a very special case of mechanical explanations. Some physical systems have nothing to do with the former, as in the case of volcanoes. Other physical systems like redwood trees cannot be understood without the former. To say that the evolutionary explanation is etiologically prior to the mechanical explanation is to say that one must approach the study of living organisms with a basic understanding of what they are and that this is something that mechanical explanations cannot provide.
Here is my take, for which Mix bears no responsibility. The relationship between the mechanistic sciences, which ask only how something happened or is what it is, and the life sciences, which ask why something happened or why it is as it is, is analogous to the relationship between the Oxford English dictionary and a good English grammar, on the one hand, and Shakespeare’s Richard the Third on the other hand.
Ignoring poetic license for the moment, Shakespeare was limited to a specific number of letters, a large but finite vocabulary, a large but finite number of grammatical rules, as well as a brevity dictated by the realities of the stage. Given those restraints, an astronomically vast but finite number of plays was possible. If you don’t believe me, read Jorge Luis Borges’ famous story, “The Library of Babel.” It’s a good but sad joke to say that all one needs is a dictionary because all the other books are in it. To get Dickey Three out of the OED, among the vast alternative populations, you need Shakespeare.
To get William Shakespeare out of the vast possibilities that the physical kosmos offers, you need what? It is hardly clear. We have no good idea how life arose out of the chemical soups, sunlight, and lightening scoured landscapes that the earth offered just before it began to fruit. Fruit it did, and the playwright known as natural selection has been scribbling furiously ever since.
Just as an interpreter of Shakespeare must begin with the play and not the dictionary, so a biologist must begin with living organisms and not with the periodic table of elements. Organic chemistry is organic first and chemical second. Of course here the analogy breaks down. The dictionary doesn’t tell you much about the play. Chemistry and physics tell you a lot about living organisms. Why are there a lot of animals here and not so many there? Sunlight and temperature tell you a lot about why there are trees with certain kinds of leaves and that tells you why there are a lot of creates that eat the leaves and predators that eat the leaf eaters.
I like the notion of nested explanations because it seems to reflect the most basic human reality. We are nested within the biosphere on the surface of this planet. We thrive on certain geographies and not so much or at all on others. The biosphere is also nested in a larger range, but still only a sliver of the world. Outside, there is the too cold or too hot and the empty silence.
As Mix observes, Aristotle was good at nesting one kind of explanation within another. He saw no contradiction between material and mechanistic causation, on the one hand, and the power of organic forms and teleological processes on the other. He might have been the last great philosopher to be altogether comfortable with all the ways that science could offer for understand the physical and existential realities of our life on this world. I must admit that I am a little uncomfortable with that.
Discomfort drives the history of philosophy and science. Still, both must continue to pursue the final view that will integrate and resolve all the problems. Just right now, I am feeling some of Aristotle’s confidence.