Is evolutionary biology about to prove a two-millennia old metaphysical speculation? Or is metaphysics about to fundamentally change the way we look at biology? Andreas Wagner, a developmental biologist at the University of Zurich, argues for both theses. I’m not convinced.
Just read the last two sentences of his 2014 book, Arrival of the Fittest: How Nature Innovates. They come in an epilogue, titled “Plato’s Cave.” “We are shedding new light on one of the most durable and fascinating subjects in all of philosophy,” he writes. “And we learn that life’s creativity draws from a source that is older than life, and perhaps older than time.” (Italics mine.) The source of this creativity, Wagner argues, is “nature’s libraries.” It’s a metaphor for an abstract storehouse of information that we can never physically encounter. “These libraries and texts,” he writes, “are concepts, mathematical concepts, touchable only by the mind’s eye.” This is Platonism, and Wagner’s not shy about admitting it. Are conceptual truths discovered, or invented? Platonists believe the former, and “Platonism,” Wagner writes, “has the upper hand in this debate.”
I have known Wagner for years (we met a couple of times, but I am very familiar with his writings in biology), and I can say without hesitation that he is one of the most interesting and provocative theorists out there. Last year, he published an essay in Aeon titled, “Without a library of Platonic forms, evolution couldn’t work.” I beg differ.
Wagner tells us that a fundamental unit in biological classification is the species. It is true that species are a more crucial level in the taxonomic hierarchy than both levels below (sub-species, races) and above (genus, family, order). But Wagner begins to veer off the main course of modern biology when he talks about the “essence” of species, which he links directly to Platonism: “A systematist’s task”—of organizing biological forms in nested, highly branching trees, or clades—“might be daunting, but it becomes manageable if each species is distinguished by its own Platonic essence,” he writes. “For example, a legless body and flexible jaws might be part of a snake’s essence, different from that of other reptiles. Indeed, the essence really is the species in the world of Platonists. To be a snake is nothing other than to be an instance of the form of the snake.”
No, definitely not. Modern biology has long since rejected any talk of “essence.” Indeed, Darwin was what we might call a species anti-realist: He thought species are arbitrary boundaries drawn by humans for their own convenience, not reflective of any deeper metaphysical reality. Second, no, snakes cannot reasonably be thought of as “nothing other than an instance of the Form of the snake.” Not only is that idea scientifically inert (how do we study these Forms? Where are they?), it is also a way of seeing things that is in serious tension with the whole concept of evolution.
Snakes are a group of reptiles that likely evolved from burrowing lizards back in the Cretaceous, some 66 million years ago. This means that they acquired their supposed Platonic Form gradually, first by passing through a two-legged stage (in the fossil known as Najash rionegrina), a species with hind limbs but lacking connection between the pelvic bones and the vertebrae (as in Haasiophis, Pachyrhachis and Eupodophis). Who knows what future evolution has in store for the descendants of today’s snakes. To say that what we see now somehow represents the Platonic terminus of an evolutionary process is entirely groundless.
Wagner is aware of this sort of objection, and indeed brings up the so-called “glass lizard,” legless and indistinguishable from a snake yet classified among lizards on the basis of a number of other anatomical traits. He also mentions the Cretaceous “snakes” with rudimentary hind legs. Because of these cases, the famed 20th century evolutionary biologist Ernst Mayr called Plato “the great anti-hero of evolutionism.” But Wagner insists that Plato will have the last word—we just need to dig deeper. He quotes the 1905 biologist Hugo De Vries, one of the re-discoverers of the work of Mendel, who established genetics and was skeptical of Darwin. De Vries famously said: “Natural selection can explain the survival of the fittest, but it cannot explain the arrival of the fittest.”
This is odd because the reconciliation of genetics and Darwinism is one of the crowning achievements of 20th century biology, the so-called Modern Synthesis. It incorporates the ideas of common descent, natural selection, mutation, and recombination into a general mathematical theory of how evolution works. Harking back to De Vries would seem to be a dead-end but, undeterred, Wagner introduces the metaphor—presumably taking inspiration from Jorge Luis Borges—of “nature’s libraries” to clarify why he doesn’t seem himself walking toward a dead end.
We are to imagine a library containing all possible sequences of DNA, not unlike one that might contain all possible combinations of letters in the alphabet. In the latter, we’d recognize neighboring entries—say, Darwin’s Origin of Species and the similar Orygyn of Spesies. Some of the neighbors may actually change the meaning of a word, while still be readable in sensible English, for instance with a “mutation” transforming GOLD into MOLD.
Wagner sees the genomic equivalent of the library arranged in the same way. This library will describe all functional proteins, as well as a bunch that will never work. All DNA sequences that maintain the same functional protein, or all sequences that change amino-acids in the protein while retaining functionality, are connected by single steps, so that one can traverse the entire library without having to make huge jumps across a bunch of sequences that would be non-functional and therefore fatal. In the English text version, it would be like never encountering an unreadable version of Origin of Species.
The question Wagner believes he’s answered is: “Since mutation is random, how does natural selection ‘know’ how to find its way in the very, very large library of possible forms?” As he says: “Without these pathways of synonymous texts, these sets of genes that express precisely the same function in ever-shifting sequences of letters, it would not be possible to keep finding new innovations via random mutation. Evolution would not work.”
Yes it would! Natural selection does the work of “walking” a population through the library, and it is the combination of a random process (mutation) and a non-random one (selection) that yields evolutionary change. But the library doesn’t exist before natural selection “walks” through it. The analogy is misleading: It is better to think of a library that is created (and partially destroyed) moment by moment as life evolves. There is no mystery here, and there hasn’t been for about a century. Thinking in terms of libraries and Platonic Forms is simply not helpful to the biologist.
Wagner is forced to compound the unnecessary complexity of his solution by trying to answer a further mystery: “So nature’s libraries and their sprawling networks go a long way towards explaining life’s capacity to evolve. But where do they come from? They exist in a world of concepts, the kind of abstract concepts that mathematicians explore. Does that make them any less real?”
Yes, of course it does. What does it mean for an abstract concept, or a possibility, to “exist”? These are the very same questions faced by mathematical Platonists, and biological Platonism—like its mathematical counterpart—simply seems to conjure up a problem where none existed before. Short on arguments, Wagner resorts to name-dropping illustrious fellow-Platonists like Charles Fefferman, winner of the Fields medal. Wagner writes, “He expressed his experience when breaking new mathematical ground this way: ‘There’s something awe-inspiring. You aren’t creating. You’re discovering what was there all the time, and that is much more beautiful than anything that man can create.’” Wagner is awed by the fact that, “for whatever reason, reality appears to obey certain mathematical formulae” we can discover. “In physics,” he writes, “the Nobel laureate Eugene Wigner called it ‘the unreasonable effectiveness of mathematics.’ And indeed, it is not clear why Newton’s law of gravitation should describe everything from accreting planets to entire solar systems and rotating galaxies. Except that it does.”
To take it in reverse order: First, reality doesn’t “obey” mathematical formulae. That’s backwards. Rather, mathematical formulae are human inventions that more or less accurately describe reality. Second, Newton’s law is actually wrong; and General Relativity, of which Newton’s law is an approximation, is in some sense wrong or incomplete in turn—it’s hardly a Platonic truth. Third, every pro-Platonist quote by an eminent scientist or mathematician or philosopher can be matched by a skeptic of equal rank. Take Albert Einstein: “As far as the laws of mathematics refer to reality, they are not certain; and as far as they are certain, they do not refer to reality.”
In philosophy of science, we like to keep metaphysics to the necessary minimum, and Platonism simply multiplies ontologies gratuitously, without any payback in either philosophy or science.
Massimo Pigliucci is chair of the philosophy department at CUNY-Lehman and the author of Answers for Aristotle: How Science and Philosophy Can Lead Us to a More Meaningful Life. Follow him on Twitter @mpigliucci.
Watch: “I love talking with philosophers,” the MIT theoretical physicist Max Tegmark says. “They are so annoying!”
The lead image is courtesy of Dave Scriven via Flickr.
A version of this post, from Plato’s Footnote, was reprinted with permission from Massimo Pigliucci.