Arrival of the Fittest: Solving Evolution's Greatest Puzzle (2 page)

S
allie 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.”
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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.
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Contrast this with an ever-changing evolving world, where species incessantly spew forth new species that can blend with each other.
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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

A special creation of each species would leave all these threads of knowledge in a messy tangle. Darwin, one of the greatest synthesizers of all time, wove them into the beautiful fabric of his theory. He threw the gauntlet at creationists by claiming that
all
life shares a common ancestor, and thereby dismissed biblical Genesis from the debate table.

That was Darwin’s first great insight. The second one was the central role of natural selection, an insight inspired by the spectacular success of animal and plant breeders.
¹⁴
The
Origin
’s entire first chapter marvels at the diversity of domestic dogs, pigeons, crop plants, and ornamental flowers that human breeders had produced. It is indeed stunning to think that humans could create Great Danes, German shepherds, greyhounds, bulldogs, and Chihuahuas, all from a common lupine ancestor, and all within mere centuries. Darwin realized that natural selection is not so different from such human selection, except that it operates on a much grander scale, and over eons of time. Nature incessantly creates new variants of organisms, most inferior, a few of them superior, and all of these variants must pass through the sieve of natural selection. Only individuals best adapted to their environment survive, procreate, and give rise to further variants. Given enough time, this process helps explain all of life’s diversity, so much so that the geneticist Theodosius Dobzhansky could say in 1973 that “nothing in biology makes sense except in the light of evolution.”

From the very beginning, that light shone more brightly on some of life’s mysteries than on others. One of them was left in especially deep shadows: the mechanism of heritability. Without some mechanism that guarantees faithful inheritance from parents to offspring, adaptations—a bird’s wing, a giraffe’s neck, a snake’s fangs—cannot persist over time. And without inheritance, selection would be powerless. Darwin himself had no idea why children resemble their parents, and his frankness in admitting ignorance is disarming. “The laws governing inheritance are for the most part unknown,” he said in the
Origin.
¹⁵

Darwin’s theory was a bit like that first movie of a galloping horse, revolutionary when compared to still photography, but only a modest step on the path to full-length feature films. The next step on biology’s path—explaining inheritance—was already made by the time Darwin died, but he did not know it. Nor did any other prominent scientist, although decisive experiments had already started in 1856, three years before Darwin published the
Origin.
¹⁶
Even the scientist who performed these experiments would not live to see the avalanche of progress he triggered, which would eventually engulf all of biology.

That scientist was the Austrian monk Gregor Mendel, who studied in Vienna and entered St. Thomas Abbey in Brno, where he would experiment on more than twenty thousand pea plants before he became abbot. For his experiments, he deliberately chose pea plants that differed in several discrete features: One plant might produce smoothly round yellow peas, whereas the other would produce wrinkly green peas, but none with in-between color or shape. Other pea plants differed sharply in flower color, pod shape, or stem length. Mendel cross-fertilized these plants and analyzed their offspring, thousands and thousands of plants.

What he saw was that these features often do not blend in the offspring.
¹⁷
The offspring’s first or second generation produces either round or wrinkly peas, but none with an intermediate shape. And different features can be inherited independently, such that the offspring might sport combinations—round and green, wrinkly and yellow—that neither parent harbored. The causes of inheritance behaved like discrete and indivisible particles. Each parent carried two particles responsible for traits like roundness or color, but would pass only one of them on to its offspring. Different features were inherited through different kinds of particles, and could thus combine and recombine independently.

Mendel worked in an academic backwater far from the intellectual currents of his time. And he committed the error that snuffed many an academic career, then and now: He published little and in the wrong place—in his case a local naturalist journal.
¹⁸
And as bad luck would have it, the abbot who succeeded him would burn Mendel’s papers after his death. But thirty-four years after its publication in 1865, Mendel’s sleeping beauty of a discovery would be roused by the Dutch botanist Hugo de Vries, who independently performed experiments similar to those of Mendel. Historians still argue whether he truly rediscovered Mendel’s laws, or whether he learned about Mendel’s work during his own experiments and tried to hide his knowledge.
¹⁹
The searing disappointment of having not just been scooped, but scooped by three decades, could certainly explain the impulse to rewrite history. Be that as it may, rediscovered Mendel’s laws were, and from then on they spread like wildfire. They became the basis of a whole new branch of biology, the science of genetics. Traits that behave as Mendel described exist in many plants and animals, including humans. Some of our Mendelian traits are as odd as the consistency of ear wax (wet or dry), but others are as important as the major blood groups (A or B), or diseases like sickle-cell anemia.