Andreas Wagner flirts with Platonism. Flirts actually is too weak a word. The Swiss evolutionary biologist embraces it. Platonism is not a fashionable idea these days--but when your work confronts you with the idea that behind the world of living organisms is a vast library Nature has in store for every possibility, you have to think twice.
Metaphors can be overdone, but in a very real sense Wagner has spent the past 15 years and more uncovering the existence of an astronomically large virtual library of genetic texts which evolution has been exploring since life began.
Arrival of the Fittest: How Nature Innovates, now out in paperback from Current, an imprint of Penguin Random House, is his story. It focuses on the blind side of Darwin's theory: not natural selection, but the raw material on which natural selection works, the random step by step process of organisms as they search, generation by generation, through a great library of genetic texts and come up with vastly different ways to 'spell' success--that is to say, 'survive'.
Innovation, of course, is the one thing the blind process of evolution is supposed to be incapable of. But Wagner, who has his own lab at University of Zurich, hit on a way of testing this.
Simply, by doing what evolution does: journey through the library and edit genomes— through a series of gene transfer or deletion events that add or eliminate at least one gene, one enzyme, or one reaction. The starting point does not have to be special, either. It could be any text in the library of genetic codes, any text that encodes, for example, a metabolism viable on glucose or on any other fuel.
So let’s start with a metabolism viable on glucose, and either delete a randomly chosen reaction or add a randomly chosen reaction from the known reaction universe. Nature would make a simple and brutal evaluation of the new text: life or death. But we scientist travelers are privileged, because we can retrace our steps. We compute the meaning of the altered text, and, if it turns out not to be viable on glucose, return to the starting text, and add or delete another random reaction— remember, there are five thousand ways of doing that. But if the neighbor is viable on glucose, the journey continues. We add or delete a second reaction, compute the phenotype, and repeat, more or less ad infinitum.
In other words, step from a starting text to its neighbor, then to the neighbor’s neighbor, to the neighbor’s neighbor’s neighbor. Wagner wanted to see how far you could walk Darwin's random walk without ever changing its chemical meaning, viability on glucose.
"Because each step alters a text at random, this walk is a random walk through the metabolic library, similar to how a drunkard might stagger home from a night out at the bar, with one difference: Each step in our random walk must encounter a text with the same meaning, the same phenotype."
Further:
If there were only one metabolism viable on glucose, this random walk would lead literally nowhere, because the starting text would have no viable neighbors. We would be rooted to the spot. The same would be true if there were a few such texts scattered widely through the library— we could not reach them without destroying viability on the way. And even if they were close together the random walk might not lead far. A few neighbors of the starting text might be viable, but their neighbors might not be.
It all started in 2006, when Wagner and his assistant Joâo Rodrigues began testing the bacterium E. Coli's viability on glucose— the ability to synthesize all its sixty-odd essential biomass molecules from this single sugar.
They pursued ever more distant 'random walks' from the original genetic code and became more and more astonished at how far the text could change--and still function. The furthest viable metabolism his lab discovered shared only 20 percent of its reactions with E. coli. "We had walked, computationally speaking, almost all the way through the library— 80 percent of the distance that separates the furthest volumes— before we were finally unable to find a glucose-viable text by taking a single step."
Since then, Wagner and his team have tested even more species and processes.
"What we have found so far already tells us that there is much more to evolution than meets the eye," he writes. "It tells us that the principles of innovability are concealed, even beyond the molecular architecture of DNA, in a hidden architecture of life with an otherworldly beauty."
Wagner's years of living and training in the U.S. before he moved back to Switzerland serve him well in his prose. Given the complicated nature of his experiments, he describes them lucidly and with the enthusiasm of a hands-on mechanic.
The partnering of mathematics with biology has made him a convert to the world of forms. But the famous “unreasonable effectiveness” of mathematics is not the only reason to believe in the reality of nature’s libraries and their genotype networks, he writes at the close of his book.
Another is that the technology of the twenty-first century grants us unrestricted access to these libraries. In so doing it can shift the debate about discovery versus invention— uncomfortably abstract for millennia— from its traditional focus on languages like that of mathematics to incorporate experimental science. The reason is that we now can read individual volumes in nature’s libraries. We can, for example, manufacture any volume of the protein library— any amino acid sequence at all— and study its chemical meaning with the instruments of biochemistry. Many of these volumes were discovered by other organisms long before us, and their molecular meaning has surprised us greatly, as antifreeze proteins, crystallins, and Hox regulators testify. It’s a safe bet that nature’s libraries will continue to surprise us— more than anything we just invented.
It's a thrilling realization, he writes. "When we begin to study nature’s libraries we aren’t just investigating life’s innovability or that of technology. We are shedding new light on one of the most durable and fascinating subjects in all of philosophy.
"And we learn that life’s creativity draws from a source that is older than life, and perhaps older than time."
Arrival of the Fittest is 290 pages, with detailed notes and bibliography. Highly recommended.
Follow me on Facebook and Twitter. Subscribe to my Vimeo Channel.
