The Violinist's Thumb: And Other Lost Tales of Love, War, and Genius, as Written by Our Genetic Code (28 page)

Once again DNA humbles and muddies our view of
ourselves. And
apoE
is just one of many cases where DNA research has transformed our knowledge of our ancient selves: filling in forgotten details in some narratives, overthrowing long-held beliefs in others, but always, always revealing how fraught hominid history has been.

To appreciate how much DNA can supplement, annotate, or plain rewrite ancient history, it helps to look back to the days when scholars first started digging up human remains and studying them—the beginnings of archaeology and paleontology. These scientists started off with confidence about human origins, were thrown into confusion by unsettling finds, and only recently flowed back toward (if not all the way to) clarity, thanks largely to genetics.

Except in unnatural cases, like Dutch sailors massacring dodos, virtually no scientist before 1800 believed that species went extinct. They had been created as is, and that was that. But a French naturalist named Jean-Léopold-Nicolas-Frédéric Cuvier upended this notion in 1796. Cuvier was a formidable man, half Darwin, half Machiavelli. He later latched onto Napoleon and rode the little dictator’s blue coattails to the pinnacle of European scientific power; by life’s end, he was Baron Cuvier. But along the way the baron proved himself one of the great naturalists ever (his power wasn’t undeserved), and he built an authoritative case that species could in fact vanish. The first clue came when he recognized that an ancient pachyderm, unearthed in a quarry near Paris, had no living descendants. Even more spectacularly, Cuvier disproved old legends about the so-called
Homo diluvii testis
skeleton. These bones, unearthed years before in Europe, resembled a deformed man with stunted limbs. Folklore had identified “him” as one of the lecherous and corrupted folk that God had expunged with Noah’s flood. The less credulous
Cuvier correctly identified the skeleton as, of all things, a titanic salamander that had long ago disappeared from the earth.

Still, not everyone believed Cuvier about the impermanence of species. The keen amateur naturalist (and U.S. president) Thomas Jefferson instructed Lewis and Clark to keep their eyes peeled inside the Louisiana Territory for giant sloths and mastodons. Fossils of both creatures had previously turned up in North America, drawing huge crowds to dig sites. (Charles Willson Peale’s painting
The Exhumation of the Mastodon
captures the scene elegantly.) Jefferson wanted to track down living examples of these beasts for patriotic reasons: he was fed up with
European naturalists who, without ever coming within an ocean of America, dismissed the fauna here as sickly, weak, and stunted, a snobby theory called “American degeneracy.” Jefferson wanted to prove American wildlife was as big and hairy and virile as European beasts, and underlying his hope that mastodons and giant sloths still roamed (or inched across) the Great Plains was the belief that species cannot go extinct.

The Exhumation of the Mastodon
, by Charles Willson Peale, showing the discovery of mastodon bones in New York in 1801. U.S. president Thomas Jefferson argued that mastodons must still be lumbering across North America, and ordered Lewis and Clark to keep their eyes peeled. (MA5911, courtesy of the Maryland Historical Society)

Although William Buckland came down more with the sober extinctionists than the excitable nonextinctionists, he contributed to the debate in his characteristically flamboyant way. For his honeymoon, Buckland dragged his wife specimen hunting across Europe; and even while hiking to remote outcroppings and pickaxing rocks for fossils, he insisted on wearing black academic robes and often a top hat. In addition to bones, Buckland grew obsessed with fossilized hunks of animal shit, called coprolites, which he generously donated to museums. But Buckland made discoveries exciting enough to be forgiven his eccentricities. In one case he excavated an ancient underground predators’ lair in Yorkshire, with plenty of snarly teeth and gnawed-on skulls to wow the public. But the work had great scientific merit and bolstered the extinctionist case: the predators were cave hyenas, and since those hyenas no longer lived in England, they must have gone extinct. More profoundly—and fitting, given his proclivity for meat—Buckland identified some vast bones exhumed from an English quarry as a new species of giant reptile, the first example of the most terrifying carnivores ever, dinosaurs. He named it
Megalosaurus.
^*

However confident he was with extinct animals, Buckland wavered, even equivocated, on the more loaded question of whether ancient human lineages ever existed. Although an ordained minister, Buckland didn’t believe in the aleph-by-aleph accuracy of the Old Testament. He speculated that geological eras had existed before “In the Beginning,” eras populated with
the likes of
Megalosaurus.
Nevertheless, like virtually all scientists, Buckland hesitated to contradict Genesis regarding human origins and our special, recent creation. In 1823, when Buckland unearthed the alluring Red Lady of Paviland—a skeleton covered with seashell jewelry and dusted with red ocher makeup—he ignored plenty of contextual evidence and identified her as a witch or prostitute from no earlier than Roman times. The lady was actually thirty thousand years old (and a man). Buckland also dismissed clear evidence at another site of chipped-flint tools appearing in the same soil layer as pre-Genesis beasts like mammoths and saber-toothed tigers.

Even less forgivable, Buckland pretty much dropped a steaming coprolite on one of the most spectacular archaeological discoveries ever. In 1829 Philippe-Charles Schmerling unearthed, among some ancient animal remains, a few uncanny, human-but-not-quite-human bones in Belgium. Basing his conclusions especially on skull fragments from a child, he suggested they belonged to an extinct hominid species. Buckland examined the bones in 1835 at a scientific meeting but never removed his biblical blinders. He rejected Schmerling’s theory and, instead of saying so quietly, proceeded to humiliate him. Buckland often claimed that because of various chemical changes, fossilized bones naturally stick to the tongue, whereas fresher bones don’t. During a lecture at the meeting, Buckland placed onto his tongue one of the animal bones (a bear’s) that Schmerling had found mixed in with the hominid remains. The bear bone stuck fast, and Buckland continued to lecture, the bone flopping about hilariously. He then challenged Schmerling to stick his “extinct human” bones to his own tongue. They fell off. Ergo they weren’t ancient.

Though hardly definitive proof, the dismissal lingered in the minds of paleontologists. So when more uncanny skulls turned up in Gibraltar in 1848, prudent scientists ignored them. Eight
years later—and just months after the death of Buckland, the last great Deluge scientist—miners worked loose still more of the odd bones from a limestone quarry in Germany’s Neander Valley. One scholar, channeling Buckland, identified them as belonging to a deformed Cossack who had been injured by Napoleon’s army and crawled into a cliff-side cave to die. But this time two other scientists reasserted that the remains belonged to a distinct line of hominids, a race more outcast than the biblical Ishmaelites. Perhaps it helped that, among the various bones, the duo had located an adult skullcap down to the eye sockets, which emphasized the thick, glowering brow we still associate with Neanderthals.
^*

With their eyes opened—and with the publication in 1859 of a little book by Charles Darwin—paleontologists began to find Neanderthals and related hominids across Africa, the Middle East, and Europe. The existence of ancient humans became a scientific fact. But just as predictably, the new evidence provoked new confusion. Skeletons can shift in the ground as rock formations buckle, fouling up attempts to date or interpret them. Bones also scatter and get crushed into smithereens, forcing scientists to rebuild entire creatures from a few stray molars or metatarsals—a subjective process open to dissension and differing interpretations. There’s no guarantee either that scientists will find representative samples: if scientists in AD 1,000,000 discovered what remains of Wilt Chamberlain, Tom Thumb, and Joseph Merrick, would they even classify them as the same species? For these reasons, every new discovery of
Homo
this and
Homo
that in the 1800s and 1900s incited further and often nasty debate. And decade after decade passed without the ultimate questions (Were all archaic humanoids our ancestors? If not, how many twigs of humanity existed?) becoming clearer. As the old joke went, put twenty paleontologists into a room, and you’d get twenty-one different schemes for human evolution. One
world expert in archaic human genetics, Svante Pääbo, has noted, “I’m often rather surprised about how much scientists fight in paleontology…. I suppose the reason is that paleontology is a rather data-poor science. There are probably more paleontologists than there are important fossils in the world.”

Such was the general state of things when genetics invaded paleontology and archaeology beginning in the 1960s—and
invaded
is the apt word. Despite their quarrels, U-turns, and antiquated tools, paleontologists and archaeologists had figured out a lot about human origins. They didn’t need a savior, thanks. So many of them resented the intrusion of biologists with their DNA clocks and molecular-based family trees, hotshots intent on overturning decades of research with a single paper. (One anthropologist scoffed at the strictly molecular approach as “no muss, no fuss, no dishpan hands. Just throw some proteins into a laboratory apparatus, shake them up, and bingo!—we have an answer to questions that have puzzled us for three generations.”) And really, the older scientists’ skepticism was warranted: paleogenetics turned out to be beastly hard, and despite their promising ideas, paleogeneticists had to spend years proving their worth.

One problem with paleogenetics is that DNA is thermodynamically unstable. Over time, C chemically degrades into T, and G degrades into A, so paleogeneticists can’t always believe what they read in ancient samples. What’s more, even in the coldest climates, DNA breaks down into gibberish after 100,000 years; samples older than that harbor virtually no intact DNA. Even in relatively fresh samples, scientists might find themselves piecing together a billion-base-pair genome from fragments just fifty letters long—proportionally equivalent to reconstructing your typical hardcover from strokes, loops, serifs, and other fragments smaller than the tittle on an
i.

Oh, and most of those fragments are junk. No matter where a corpse falls—the coldest polar ice cap, the driest Saharan
dune—bacteria and fungi will worm inside and smear their own DNA around. Some ancient bones contain more than 99 percent foreign DNA, all of which must be laboriously extracted. And that’s the easy kind of contamination to deal with. DNA spreads so easily from human contact (even touching or breathing on a sample can pollute it), and ancient hominid DNA so closely mirrors our own, that ruling out human contamination in samples is almost impossible.

These obstacles (plus a few embarrassing retractions over the years) have pushed paleogeneticists into near paranoia about contamination, and they demand controls and safeguards that seem a better fit for a biological warfare lab. Paleogeneticists prefer samples no human has ever handled—ideally, ones still dirty from remote dig sites, where workers use surgical masks and gloves and drop everything into sterile bags. Hair is the best material, since it absorbs fewer contaminants and can be bleached clean, but paleogeneticists will settle for less fragile bone. (And given the paucity of uncontaminated sites, they often settle for bones in museum storage lockers, especially bones so boring no one ever bothered studying them before.)

The sample selected, scientists bring it into a “clean room” maintained at higher-than-normal air pressure, so that air currents—and more to the point, the floating scraps of DNA that can ride around on air currents—cannot flow inward when the door opens. Anyone allowed inside the room dresses toe to top in sterile scrubs with face masks and booties and two pairs of gloves, and they get pretty used to the odor of the bleach swabbed over most surfaces. (One lab bragged that its technicians, presumably while in their suits, are given sponge baths in bleach.) If the sample is bone, scientists use dentist drills or picks to shave off a few grams of powder. They might even doctor the drill so it rotates only at 100 rpm, since the heat of a standard, 1,000-rpm drill can fry DNA. They then dissolve the nib of
powder with chemicals, which liberates the DNA. At this point paleogeneticists often add tags—snippets of artificial DNA—to every fragment. That way they can tell if extraneous DNA, which lacks the tag,
^*
ever infiltrates the sample after it leaves the clean room. Scientists might also note the racial backgrounds of technicians and other scientists (and probably even janitors) at the lab, so that if unexpected ethnic sequences show up, they can judge whether their sample was compromised.