Arrival of the Fittest: Solving Evolution's Greatest Puzzle
Page 1
CURRENT
Published by the Penguin Group
Penguin Group (USA) LLC
375 Hudson Street
New York, New York 10014
USA | Canada | UK | Ireland | Australia | New Zealand | India | South Africa | China
penguin.com
A Penguin Random House Company
First published by Current, a member of Penguin Group (USA) LLC, 2014
Copyright © 2014 by Andreas Wagner
Penguin supports copyright. Copyright fuels creativity, encourages diverse voices, promotes free speech, and creates a vibrant culture. Thank you for buying an authorized edition of this book and for complying with copyright laws by not reproducing, scanning, or distributing any part of it in any form without permission. You are supporting writers and allowing Penguin to continue to publish books for every reader.
Illustrations by the author
LIBRARY OF CONGRESS CATALOGING-IN-PUBLICATION DATA
Wagner, Andreas, 1967 January 26–
Arrival of the fittest : solving evolution’s greatest puzzle / Andreas Wagner.
pages cm
Includes bibliographical references and index.
eBook ISBN 978-1-101-62816-4
1. Natural selection. 2. Evolutionary genetics. I. Title.
QH375.W327 2014
572.8'38—dc23 2014009774
While the author has made every effort to provide accurate telephone numbers and Internet addresses at the time of publication, neither the author nor the publisher is responsible for errors, or for changes that occur after publication. Further, the publisher does not have any control over and does not assume any responsibility for author or third-party websites or their content.
Version_1
CONTENTS
Title Page
Copyright
PROLOGUE
World Enough, and Time
CHAPTER ONE
What Darwin Didn’t Know
CHAPTER TWO
The Origin of Innovation
CHAPTER THREE
The Universal Library
CHAPTER FOUR
Shapely Beauties
CHAPTER FIVE
Command and Control
CHAPTER SIX
The Hidden Architecture
CHAPTER SEVEN
From Nature to Technology
EPILOGUE
Plato’s Cave
ACKNOWLEDGMENTS
NOTES
BIBLIOGRAPHY
INDEX
PROLOGUE
World Enough, and Time
In the spring of 1904, Ernest Rutherford, a thirty-two-year-old New Zealand–born physicist then working at McGill University in Canada, gave a lecture at the world’s oldest scientific organization, the Royal Society of London for Improving Natural Knowledge. His subject was radioactivity and the age of the earth.
At that time, scientists had long since forsworn the biblical accounts asserting that the earth was only six thousand years old. The most widely accepted dates had been calculated by another physicist—William Thomson, better known as Lord Kelvin—who had used the equations of thermodynamics and the earth’s heat conductivity to estimate that the planet was somewhere around twenty million years old.
In geology, that’s not a lot of time, and the implications were profound. The earth’s geological features could not have appeared within this duration if processes like volcanism and erosion proceeded at today’s rate.1 But the real victim of Kelvin’s estimate was Charles Darwin’s theory of evolution by natural selection. Darwin had described himself as “greatly troubled at the short duration of the world according to Sir W. Thomson.”2 He knew that organisms had not changed much since the last ice ages, and from such little change he inferred that the amount of time needed to create all organisms—alive today or preserved in fossils—must be truly enormous.3 Twenty million years was not enough time to create life’s diversity.
But Rutherford, who had discovered the phenomenon of radioactive half-life only a few years before, knew that Kelvin was wrong, by at least several orders of magnitude. As he later recalled:
I came into the room, which was half dark, and presently spotted Lord Kelvin in the audience and realized that I was in for trouble at the last part of the speech dealing with the age of the earth, where my views conflicted with his. . . . The discovery of the radio-active elements, which in their disintegration liberate enormous amounts of energy, thus increases the possible limit of the duration of life on this planet, and allows the time claimed by the geologist and biologist for the process of evolution.4 (emphasis added).
And that was that. Kelvin died in 1907. Rutherford won the Nobel Prize in 1908, and by the 1930s his radiometric methods had shown that the earth was around 4.5 billion years old. Darwin’s theory was saved, since the processes of random mutation and selection now had the time needed to create life’s enormous complexity and diversity.
Or did they?
Consider the peregrine falcon, Falco peregrinus, one of nature’s great predators and an organism of marvelous perfection. Its powerful musculature, matched with an extremely lightweight skeleton, makes it by far the fastest animal on earth, able to reach more than 200 miles per hour in one of its characteristic dives. All that speed translates into enormous kinetic energy when the falcon strikes its prey in midair with razor-sharp talons. If that impact alone does not deliver death, the falcon can sever the spinal column of its prey with a conveniently notched upper beak.5
Before moving in for the kill, F. peregrinus needs to track down its prey. The targeting mechanism is a pair of eyes with full-color binocular vision, possessing resolving power more than five times greater than a human’s, which means that a peregrine can see a pigeon at distances of more than a mile.6 Like many predators, the falcon has an eye with a nictitating membrane—a third eyelid—a bit like a windshield wiper that removes dirt while keeping the eye moist during a high-speed chase. The falcon’s eyes also harbor more photoreceptors, the rods that capture images in very low light, and the cones that provide color vision. 7 Its photoreceptors render even long-wavelength ultraviolet light visible.
A marvel indeed. But even more marvelous is knowing that every one of those brilliant adaptations is the sum of innumerable tiny steps, each one preserved by natural selection, each one a change in a single molecule. The deadly beak and talons of F. peregrinus are built from the same raw material as its feathers, the protein molecules known as keratin, the human versions of which make up your hair and nails.8 For color vision, those extraordinary eyes depend on opsins, protein molecules in the eyes’ rods and cones. Crucial for their remarkable acuity are their lenses, composed of transparent proteins known as crystallins.9
The first vertebrates to use crystallins in lenses did so more than five hundred million years ago, and the opsins that enable the falcon’s vision are some seven hundred million years old.10 They originated some three billion years after life first appeared on earth. That sounds like a helpfully long amount of time to come up with these molecular innovations. But each one of those opsin and crystallin proteins is a chain of hundreds of amino acids, highly specific sequences of molecules written in an alphabet of twenty amino acid letters. If only one such sequence could sense light or help form a transparent cameralike lens, how many different hundred-amino-acid-long protein strings would we have to sift through? The first amino acid of such a string could be any one of the twenty kinds of amino acids, and the same holds for the second amino acid. Because 20 × 20 = 400, there are there are 400 possible strings of two amino acids. Consider also the third am
ino acid, and you have arrived at 20 × 20 × 20, or 8,000, possibilities. At four amino acids we already have 160,000 possibilities. For a protein with a hundred amino acids (crystallins and opsins are much longer), the numbers multiply to a 1 with more than 130 trailing zeroes, or more than 10130 possible amino acid strings. To get a sense of this number’s magnitude, consider that most atoms in the universe are hydrogen atoms, and physicists have estimated the number of these atoms as 1090, or 1,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000. This is “only” a 1 with 90 zeroes. The number of potential proteins is not merely astronomical, it is hyperastronomical, much greater than the number of hydrogen atoms in the universe.11 To find a specific sequence like that is not just less likely than winning the jackpot in the lottery, it is less likely than winning a jackpot every year since the Big Bang.12 In fact, it’s countless billions of times less likely. If a trillion different organisms had tried an amino acid string every second since life began, they might have tried a tiny fraction of the 10130 potential ones. They would never have found the one opsin string. There are a lot of different ways to arrange molecules. And not nearly enough time.
When the seventeenth-century lyric poet Andrew Marvell bemoaned, “Had we but world enough, and time” to avoid the “deserts of vast eternity” that lay before him, he was attempting to unlock his mistress’s bedchamber, not the secrets of nature. But he was on to something. Common wisdom holds that natural selection, combined with the magic wand of random change, will produce the falcon’s eye in good time. This is the mainstream perspective on Darwinian evolution: A tiny fraction of small and random heritable changes confers a reproductive advantage to the organisms that win this genetic lottery and, accumulating over time, such changes explain the falcon’s eye—and, by extension, everything from the falcon itself to all of life’s diversity.
The power of natural selection is beyond dispute, but this power has limits. Natural selection can preserve innovations, but it cannot create them. And calling the change that creates them random is just another way of admitting our ignorance about it. Nature’s many innovations—some uncannily perfect—call for natural principles that accelerate life’s ability to innovate, its innovability.
For the d last fifteen years, I have been privileged to help uncover these principles, first in the United States and later, joined by a group of highly talented researchers, in my laboratory at the University of Zürich in Switzerland. Using experimental and computational technologies unimagined by Darwin or Rutherford, our goal is not to discover individual innovations, but to find the wellsprings of all biological innovation. What we have found so far already tells us that there is much more to evolution than meets the eye. 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.
These principles are the subject of this book.
CHAPTER ONE
What Darwin Didn’t Know
Sallie Gardner was the world’s first movie star. Her graceful debut in 1878 launched cinema itself, though she was only six years old. Sallie, you see, happened to be the Thoroughbred horse that the English-born photographer Eadweard Muybridge shot in full gallop with his zoopraxiscope, an array of twenty-four cameras along her path, to settle a pressing question that undoubtedly keeps many people awake at night: Does a galloping horse ever lift all four legs off the ground? (The answer is yes.) His grainy, jerky silent movie, all of a second long, is worlds apart from the high-definition digital surround-sound cinematography taken for granted in the early twenty-first century. Yet the time separating Muybridge’s photographic study from modern movies spans just over a century, a stretch not much longer than the time since Darwin published The Origin of Species, only nineteen years before Sallie Gardner’s star turn.
During the same time, biology has been transformed by a revolution even more dramatic than the cinematic one.1 This revolution has revealed a world as inaccessible to Darwin as outer space was to cavemen. And it has helped to answer the single most important question about evolution, the question that Darwin and generations of scientists after him did not, could not touch: How does nature bring forth the new, the better, the superior? How does life create?
You might be puzzled. Wasn’t that exactly Darwin’s great achievement, to understand that life evolved and to explain how? Isn’t that his legacy? Yes and no. Darwin’s theory surely is the most important intellectual achievement of his time, perhaps of all time. But the biggest mystery about evolution eluded his theory. And he couldn’t even get close to solving it. To see why, we first need to take a look at what Darwin knew and what he didn’t, what was new about his theory and what wasn’t, and why only now, more than a century later, can we begin to see how the living world creates.
Germs of thought about an evolving natural world existed long before Darwin. No fewer than twenty-five hundred years ago, the Greek philosopher Anaximander—better known as the great-grandfather of the heliocentric worldview—thought that humans emerged from fish. The fourteenth-century Muslim historian Ibn Khaldun thought that life progressed gradually from minerals to plants to animals. Much later, the nineteenth-century French anatomist Etienne Geoffroy Saint-Hilaire deduced from fossilized reptiles that they had changed over time.2 The Viennese botanist Franz Unger argued in 1850, just a few years before Darwin published The Origin of Species in 1859, that all other plants descend from algae.3 And the French zoologist Jean-Baptiste Lamarck postulated that evolution occurred through use and disuse of organs. Some of the earliest thinkers even seem prescient about evolution, until you dig a bit and find some bizarre nuggets, such as Anaximander’s notion that early humans lived inside fish until puberty, when their hosts burst and released them. Beliefs that are alien to today’s science persisted well into Darwin’s era. According to one of them, shared by many from the ancient Greeks to Lamarck, simple organisms are spontaneously created from inanimate matter like wet mud.4
Just as evolution had its proponents, it had equally vocal opponents well into Darwin’s era. And no, I do not mean people like today’s young earth creationists—half literate and wholly ignorant—who believe that earth was created on a Saturday night in October of 4004 BC (and that Noah’s Ark could have saved more than a million species, but Noah somehow forgot the huge dinosaurs, perhaps forgivably so, considering that he was six hundred years old). I mean scientific leaders of the time. One of them was the French geologist Georges Cuvier, the founder of paleontology, literally the science of “ancient beings” (think dinosaurs).5 He discovered that the fossils embedded in older rocks are quite different from those in younger rocks, which resemble today’s life. Yet he thought that each species had essential, immutable characteristics, and could only vary in superficial traits. Another example is Carl Linnaeus, who lived a mere century before Darwin. He is the father of our modern system for classifying life’s diversity, yet until late in life he did not believe in evolution’s great chain of living beings.6
Christian beliefs are the best-known reason for such resistance. To Cuvier, life’s diversity wasn’t evidence of evolution but of the Creator’s great talents. Another reason, however, has even deeper roots. It goes back all the way to the Greek philosopher Plato, whose influence on Western philosophy is so great that the twentieth-century philosopher Alfred North Whitehead demoted all of European philosophy to “a series of footnotes to Plato.”7 Plato’s philosophy was deeply influenced by the ideal, abstract world of mathematics and geometry. It maintains that the visible, material world is but a faint, fleeting shadow of a higher reality, which consists of abstract geometric forms, such as triangles and circles. To a Platonist, basketballs, tennis balls, and Ping-Pong balls share an essence, their ball-like shape. It is this essence—perfect, geometric, abstract—that is real, not the physical balls, which are as fleeting and changeable as shadows.
The goals of scientists like
Linnaeus and Cuvier—to organize the chaos of life’s diversity—are much easier to achieve if each species has a Platonic essence that distinguishes it from all others, in the same way that the absence of legs and eyelids is essential to snakes and distinguishes them from other reptiles. In this Platonic worldview, the task of naturalists is to find the essence for each species. Actually, that understates the case: In an essentialist world, the essence really is the species.8 Contrast this with an ever-changing evolving world, where species incessantly spew forth new species that can blend with each other.9 The snake Eupodophis from the late Cretaceous period, which had rudimentary hind legs, and the glass lizard, which is alive today and lacks legs, are just two of many witnesses to the blurry boundaries of species. Evolution’s messy world is anathema to the clear, pristine order that essentialism craves. It is thus no accident that Plato and his essentialism became the “great antihero of evolutionism,” as the twentieth-century zoologist Ernst Mayr called it.10
In the controversy between Darwinists and their opponents, fossils like Eupodophis were mere boulders in a mountain of evidence that helped Darwin’s supporters gain the upper hand.11 At Darwin’s time, systematists had already classified thousands of living species and unveiled deep similarities among them. Geologists had discovered that the earth’s surface was roiling, incessantly creating, folding, and crushing layers of rock. Paleontologists had discovered countless extinct species, some in young rocks and similar to the life we know, others in ancient rocks and very different. Embryologists had shown that organisms as different as a freely paddling shrimp and a barnacle clamped to a ship’s hull can have deeply similar embryos.12 Explorers, Darwin among them, had found many intriguing patterns of biogeography. Small islands have fewer species, opposite shores of the same continent harbor very different faunas, Europe and South America host completely different mammals.13