University of Zurich evolutionary biologist Andreas Wagner is the first to give Darwin his due, but in his new book, Arrival of the Fittest: Solving Evolution’s Greatest Puzzle, argues that natural selection alone cannot explain the totality of evolution. We got a chance to chat with him recently about the natural phenomena that give rise to life’s stunning innovations.
(Note: This interview has been lightly edited and condensed.)
World Science Festival: We’ve all heard of ‘survival of the fittest.’ What does ‘arrival of the fittest’ mean?
Andreas Wagner: It’s actually taken from a famous botanist, Hugo de Vries, from the last sentence of a book he wrote in 1905: “Natural selection can explain the survival of the fittest, but it cannot explain the arrival of the fittest.”
The arrival of the fittest here simply means how new traits originate. For example, there is this interesting fish called the winter flounder, which lives close to the Arctic Circle, in very deep, cold waters—so cold that our body fluids would freeze solid. Yet this fish survives there. It turns out that its ancestors discovered a new class of antifreeze proteins that work a bit similar to the antifreeze in your car.
It’s very easy to understand how natural selection could help such an innovation spread through a population of fish, since it helps them survive; but it doesn’t tell us anything about how the innovation arose in the first place. That’s a puzzle that’s been with us since Darwin’s time.
WSF: So is it all down to random chance—genes get juggled, and stuff arises?
AW: There’s a whole lot more to it. Random chance still plays a role—we know that the DNA of organisms changes randomly. But there’s actually an organization process that helps these organisms discover new things.
Think of a library that is so large that it contains all possible strings of letters. Each volume in this library contains a different string, and there would be many more volumes than there are atoms in the universe. We could call that a universal library. It would contain a lot of nonsense, but it would also contain a lot of interesting texts—your biography, my biography, the life story of every human who’s been alive, the political history of every country, all novels ever written. And it would also contain descriptions of every single technological innovation, from fire to the steam engine, to innovations we haven’t made yet. Nature innovates with libraries much like that one.
A protein is basically a string of letters, corresponding to one of 20 different kinds of amino acid building blocks in humans. A single protein could be 100 amino acids. So we can think of a library of all possible amino acid texts. When evolution changes organisms, what it does is explore this library through random changes in DNA, which are then translated by organisms into changes in the amino acid sequences of proteins. A population is like a crowd of readers that goes from one text to the next.
Now, how would you organize a library if you wanted to easily find the text on a particular technology? You would have a catalog, and have all the texts about, say, transistors in one section of the library. That works for us because we can read catalogs, but in nature’s library it’s very different. Evolution doesn’t have a catalog; its readers explore the library through random steps.
There’s also something that’s very curious about this library. You think of antifreeze proteins as being a solution to a very specific problem that nature faces: “How do I keep this fish alive?” You may think there is only one single solution to this, one amino acid strain that provides this protection. But if that were the case, evolution would have a serious problem, because the library is so huge it could never be explored in the 4 billion years life has been around, or even 40 billion years. But it turns out there is not just one text that solves the problem, there are myriad texts that all have a different amino acid sequence specifying antifreeze protection. And these texts are not clustered in one corner of the library; they’re spread out all over…
WSF: So you’re more likely to run into it!
AW: Exactly. This particular organization also helps because when you, as a reader in a library of books, pick up a text that doesn’t have any meaning, you’d put it aside. But in evolution’s libraries that’s completely different: if an organism has an antifreeze protein, and a single mutation changes the sequence and disrupts the function of the protein, it becomes useless and the organism dies. Missteps in nature’s libraries are fatal. A large network of synonymous texts ensures that nature’s readers can stay on a path that specifies, say, antifreeze function.
This network organization buys an additional benefit: As a population explores the library, near the network of synonymous texts you might find new innovations—superior antifreeze proteins, perhaps. So the peculiar organization of this library allows blind exploration, the preservation of things that work already, and the discovery of new things that allows the arrival of the fittest.
WSF: What’s the main thing you want readers to take away from the book?
AW: That there’s a fascinating world out there that Darwin didn’t have any idea about, and that really helps us explain how evolution can work. Evolution has been criticized from various quarters by people who say, “well, it can’t all just be random change.” The book shows principles that are in agreement with Darwinism, but go beyond it. There’s rhyme and reason to how life evolved.
Below, check out this vision of nature’s library from Arrival of the Fittest:
If you wandered through the universal library of books long enough, you would find books that surprise you. They contain novel thoughts, ideas, and inventions. The genotypic texts in the universal metabolic library are no different. They can encode metabolisms with never-before-seen chemical abilities, novel phenotypes that manufacture new molecules or use new fuels. In short, innovations.
Because metabolism is as old as life itself, evolving life has explored this library ever since it originated. A billion years ago, nature had already discovered unimaginably many metabolic phenotypes, enough of them that it might have stopped finding innovative metabolic texts long since. But far from resting on its early laurels, evolution is still discovering such texts, much faster than we can decipher them, in billions and trillions of organisms alive today. Some of these texts appeared less than a hundred years ago—a mere moment in evolutionary time.
Consider pentachlorophenol, a nasty molecule that humans first produced in the 1930s. It is used in antifouling paint to coat ships’ hulls, and also as an insecticide, fungicide, and disinfectant—in short, to kill life. Pentachlorophenol also damages our kidneys, blood, and nervous system, and it causes cancer. But despite its noxious nature, life has found ways not only to tolerate pentachlorophenol but to thrive on it. The aptly named bacterium Sphingobium chlorophenolicum can extract both energy and carbon from it, using pentachlorophenol as its only food source. To do so, its genome encodes four enzyme-catalyzed reactions that convert pentachlorophenol into molecules that are as digestible as glucose—the equivalent of transforming a chemical weapon into a chocolate bar.
The combination of these reactions is unique to S. chlorophenolicum, but the reactions themselves are not. Each of them occurs in hundreds if not thousands of other organisms. Two of them help recycle superfluous amino acids in some bacteria, whereas the other two disarm toxic molecules produced by some fungi and insects—molecules that happen to resemble pentachlorophenol. Like a garage mechanic building a sprinkler system out of an alarm clock, a bicycle pump, and some PVC pipe, evolution has created in S. chlorophenolicum a new arrangement of chemical reactions catalyzed by enzymes that individually exist in other organisms. In other words, metabolic innovation is combinatorial.
Reprinted from Arrival of the Fittest: Solving Evolution’s Greatest Puzzle by Andreas Wagner with permission of Current, a member of Penguin Group (USA) LLC, A Penguin Random House Company. Copyright (c) Andreas Wagner, 2014.