by Dan Ariely
Much of the discussion centers on what exactly is being synchronized—perhaps timing of ovulation, perhaps length of cycle. A review of human data from the 1990s by the father-and-son team of Leonard and Aron Weller of Bar-Ilan University in Israel found that synchrony sometimes occurs and sometimes does not. “If it exists,” Leonard Weller reported, “it is certainly not ubiquitous.”
Although she still retains the assertiveness of her college days, McClintock agrees that the effect is subtler than she thought at first. But she also believes that the critics tend to miss the more important point: that evidence for chemical communication between humans has steadily accumulated since her study. And that it is not surprising that our chemical messaging is turning out to be as intricate as every other form of human communication.
ELIZABETH KOLBERT
Sleeping with the Enemy
FROM The New Yorker
THE MAX PLANCK INSTITUTE for Evolutionary Anthropology, in Leipzig, is a large, mostly glass building shaped a bit like a banana. The institute sits at the southern edge of the city, in a neighborhood that still very much bears the stamp of its East German past. If you walk down the street in one direction, you come to a block of Soviet-style apartment buildings; in the other, to a huge hall with a golden steeple, which used to be known as the Soviet Pavilion. (The pavilion is now empty.) In the lobby of the institute there’s a cafeteria and an exhibit on great apes. A TV in the cafeteria plays a live feed of the orangutans at the Leipzig Zoo.
Svante Pääbo heads the institute’s department of evolutionary genetics. He is tall and lanky, with a long face, a narrow chin, and bushy eyebrows, which he often raises to emphasize some sort of irony. Pääbo’s office is dominated by a life-size model of a Neanderthal skeleton, propped up so that its feet dangle over the floor, and by a larger-than-life-size portrait that his graduate students presented to him on his fiftieth birthday. Each of the students painted a piece of the portrait, the overall effect of which is a surprisingly good likeness of Pääbo, but in mismatched colors that make it look as if he had a skin disease.
At any given moment, Pääbo has at least half a dozen research efforts in progress. When I visited him in May, he had one team analyzing DNA that had been obtained from a 40,000- or 50,000-year-old finger bone found in Siberia, and another trying to extract DNA from a cache of equally ancient bones from China. A third team was slicing open the brains of mice that had been genetically engineered to produce a human protein.
In Pääbo’s mind, at least, these research efforts all hang together. They are attempts to solve a single problem in evolutionary genetics, which might, rather dizzyingly, be posed as: What made us the sort of animal that could create a transgenic mouse?
The question of what defines the human has, of course, been kicking around since Socrates, and probably a lot longer. If it has yet to be satisfactorily resolved, then this, Pääbo suspects, is because it has never been properly framed. “The challenge is to address the questions that are answerable,” he told me.
Pääbo’s most ambitious project to date, for which he has assembled an international consortium to assist him, is an attempt to sequence the entire genome of the Neanderthal. The project is about halfway complete and has already yielded some unsettling results, including the news, announced by Pääbo last year, that modern humans, before doing in the Neanderthals, must have interbred with them.
Once the Neanderthal genome is complete, scientists will be able to lay it gene by gene—indeed, base by base—against the human, and see where they diverge. At that point, Pääbo believes, an answer to the age-old question will finally be at hand. Neanderthals were very closely related to modern humans—so closely that we shared our prehistoric beds with them—and yet clearly they were not humans. Somewhere among the genetic disparities must lie the mutation or, more probably, mutations that define us. Pääbo already has a team scanning the two genomes, drawing up lists of likely candidates.
“I want to know what changed in fully modern humans, compared with Neanderthals, that made a difference,” he said. “What made it possible for us to build up these enormous societies, and spread around the globe, and develop the technology that I think no one can doubt is unique to humans. There has to be a genetic basis for that, and it is hiding somewhere in these lists.”
Pääbo, who is now fifty-six, grew up in Stockholm. His mother, a chemist, was an Estonian refugee. For a time, she worked in the laboratory of a biochemist named Sune Bergström, who later won a Nobel Prize. Pääbo was the product of a lab affair between the two, and, although he knew who his father was, he wasn’t supposed to discuss it. Bergström had a wife and another son; Pääbo’s mother, meanwhile, never married. Every Saturday, Bergström would visit Pääbo and take him for a walk in the woods or somewhere else where he didn’t think he’d be recognized.
“Officially, at home, he worked on Saturday,” Pääbo told me. “It was really crazy. His wife knew. But they never talked about it. She never tried to call him at work on Saturdays.” As a child, Pääbo wasn’t particularly bothered by the whole arrangement; later, he occasionally threatened to knock on Bergström’s door. “I would say, ‘You have to tell your son—your other son—because he will find out sometime,’” he recalled. Bergström would promise to do this but never followed through. (As a result, Bergström’s other son did not learn that Pääbo existed until shortly before Bergström’s death, in 2004.)
From an early age, Pääbo was interested in old things. He discovered that around fallen trees it was sometimes possible to find bits of pottery made by prehistoric Swedes, and he filled his room with potsherds. When he was a teenager, his mother took him to visit the pyramids, and he was entranced. He enrolled at Uppsala University, planning to become an Egyptologist.
“I really wanted to discover mummies, like Indiana Jones,” he said. Mostly, though, the coursework turned out to involve parsing hieroglyphics, and instead of finding it swashbuckling Pääbo thought it was boring. Inspired by his father, he switched first to medicine, then to cell biology.
In the early 1980s, Pääbo was doing doctoral research on viruses when he once again began fantasizing about mummies. At least as far as he could tell, no one had ever tried to obtain DNA from an ancient corpse. It occurred to him that if this was possible, then a whole new way of studying history would open up.
Suspecting that his dissertation adviser would find the idea silly (or worse), Pääbo conducted his mummy research in secret, at night. With the help of one of his former Egyptology professors, he managed to obtain some samples from the Egyptian Museum in what was then East Berlin. In 1984, he published his results in an obscure East German journal. He had, he wrote, been able to detect DNA in the cells of a mummified child who’d been dead for more than two thousand years. Among the questions that Pääbo thought mummy DNA could answer were what caused pharaonic dynasties to change and who Tutankhamen’s mom was.
While Pääbo was preparing a version of his mummy paper for publication in English, a group of scientists from the University of California at Berkeley announced that they had succeeded in sequencing a snippet of DNA from a zebralike animal known as a quagga, which had been hunted to extinction in the 1880s. (The DNA came from a 140-year-old quagga hide preserved at the National History Museum in Mainz.) The leader of the team, Allan Wilson, was an eminent biochemist who had, among other things, come up with a way to study evolution using the concept of a “molecular clock.” Pääbo sent Wilson the galleys of his mummy paper. Impressed, Wilson replied, asking if there was any space in Pääbo’s lab; he might like to spend a sabbatical there. Pääbo had to write back that he could not offer Wilson space in his lab, because, regrettably, he didn’t have a lab—or even, at that point, a PhD.
Pääbo’s mummy paper became the cover article in Nature. It was also written up in the New York Times, which called his achievement “the most dramatic of a series of recent accomplishments using molecular biology.” Pääbo’s colleagues in Sweden,
though, remained skeptical. They urged him to forget about shriveled corpses and stick to viruses.
“Everybody told me that it was really stupid to leave that important area for something which looked like a hobby of some sort,” he said. Ignoring them, Pääbo moved to Berkeley to work for Wilson.
“He just kind of glided in,” Mary-Claire King, who had also been a student of Wilson’s and who is now a professor of genome sciences at the University of Washington, recalled. According to King, Pääbo and Wilson, who died in 1991, turned out to share much more than an interest in ancient DNA.
“Each of them thought of very big ideas,” she told me. “And each of them was very good at translating those ideas into testable hypotheses. And then each of them was very good at developing the technology that’s necessary to test the hypotheses. And to have all three of those capacities is really remarkable.” Also, although “they were both very data-driven, neither was afraid to say outrageous things about their data, and neither was afraid to be wrong.”
DNA is often compared to a text, a comparison that’s apt as long as the definition of “text” encompasses writing that doesn’t make sense. DNA consists of molecules known as nucleotides knit together in the shape of a ladder—the famous double helix. Each nucleotide contains one of four bases: adenine, thymine, guanine, and cytosine, which are designated by the letters A, T, G, and C, so that a stretch of the human genome might be represented as ACCTCCTCTAATGTCA. (This is an actual sequence, from chromosome 10; the comparable sequence in an elephant is ACCTCCCCTAATGTCA.) The human genome is 3 billion bases—or, really, base pairs—long. As far as can be determined, most of it is junk.
With the exception of red blood cells, every cell in an organism contains a complete copy of its DNA. It also contains many copies—from hundreds to thousands—of an abridged form of DNA known as mitochondrial DNA, or mtDNA. But as soon as the organism dies, the long chains of nucleotides begin to break down. Much of the damage is done in the first few hours, by enzymes inside the creature’s own body. After a while, all that remains is snippets, and after a longer while—how long seems to depend on the conditions of decomposition—these snippets, too, disintegrate. “Maybe in the permafrost you could go back five hundred thousand years,” Pääbo told me. “But it’s certainly on this side of a million.” Five hundred thousand years ago, the dinosaurs had been dead for more than 64 million years, so the whole Jurassic Park fantasy is, sadly, just that. On the other hand, 500,000 years ago modern humans did not yet exist.
When Pääbo arrived in California, he was still interested in finding a way to use genetics to study human history. He’d discovered, however, a big problem with trying to locate fragments of ancient Egyptian DNA: they look an awful lot like—indeed, identical to—fragments of contemporary human DNA. Thus a single microscopic particle of his own skin, or of someone else’s, even some long-dead museum curator’s, could nullify months of work.
“It became clear that human contamination was a huge problem,” he explained. (Eventually, Pääbo concluded that the sequences he had obtained for his original mummy paper had probably been corrupted in this way.) As a sort of warmup exercise, he began working on extinct animals. He analyzed scraps of mtDNA from giant ground sloths, which disappeared about 12,000 years ago, and from mammoths, which vanished around the same time, and from Tasmanian tigers, which were hunted to extinction by the 1930s. He extracted mtDNA from moas, the giant flightless birds that populated New Zealand before the arrival of the Maori, and found that moas were more closely related to birds from Australia than to kiwis, the flightless birds that inhabit New Zealand today. “That was a blow to New Zealand self-esteem,” he recalled. He also probed plenty of remains that yielded no usable DNA, including bones from the La Brea tar pits and fossilized insects preserved in amber. In the process of this work, Pääbo more or less invented the field of paleogenetics.
“Frankly, it was a problem that I wouldn’t have tackled myself, because I thought it was too difficult,” Maynard Olson, an emeritus professor at the University of Washington and one of the founders of the Human Genome Project, told me. “Pääbo brought very high standards to this area, and took the field of ancient DNA study from its Jurassic Park origins to a real science, which is a major accomplishment.”
“There’s nothing unique about most of science,” Ed Green, a professor of biomolecular engineering at the University of California at Santa Cruz who works on the Neanderthal Genome Project, said. “If you don’t do it, somebody else is going to do it a few months later. Svante is one of the rare people in science for whom that is not true. There wouldn’t even be a field of ancient DNA as we know it without him.”
“It’s a nice rarity in science when people take not only unique but also productive paths,” Craig Venter, who led a rival effort to the Human Genome Project, told me. “And Svante has clearly done both. I have immense respect for him and what he’s done.”
While Pääbo was living in California, he sometimes went to Germany to visit a woman who was attending graduate school at the University of Munich. “I had many relationships with men, but I also had girlfriends now and again,” he told me. The relationship ended; shortly afterward, the University of Munich offered Pääbo an assistant professorship. With no pressing reason to move to Germany, he demurred. The offer was increased to a full professorship: “So then I said, ‘Germany isn’t that bad after all. I’ll go there for a few years.’”
Pääbo was still in Munich several years later when he got a call from the Rhenish State Museum in Bonn. The museum houses the bones of the first Neanderthal to be identified as such, which was discovered in the summer of 1856. What did Pääbo think the odds were that he could extract usable DNA? He had no way of determining what kind of shape the bones were in until he dissolved them.
“I didn’t know what to tell them, so I said, ‘There’s a five-percent chance that it works,’” he recalled. A few months later, he received a small chunk of the Neanderthal’s right humerus.
The first Neanderthal was found in a limestone cave about forty-five miles north of Bonn, in an area known as the Neander Valley, or, in German, das Neandertal. Although the cave is gone—the limestone was long ago quarried into building blocks—the area is now a sort of Neanderthal theme park, with its own museum, hiking trails, and a garden planted with the kinds of shrubs that would have been encountered during an ice age. In the museum, Neanderthals are portrayed as kindly, if not particularly telegenic, humans. By the entrance to the building, there’s a model of an elderly Neanderthal leaning on a stick. He is smiling benignantly and resembles an unkempt Yogi Berra. Next to him is one of the museum’s most popular attractions—a booth called the Morphing-Station. For three euros, visitors to the station can get a normal profile shot of themselves and, facing that, a second shot that has been doctored. In the second, the chin recedes, the forehead slopes, and the back of the head bulges out. Kids love to see themselves—or, better yet, their siblings—morphed into Neanderthals. They find it screamingly funny.
When the first Neanderthal bones showed up in the Neander Valley, they were treated as rubbish (and almost certainly damaged in the process). The fragments—a skullcap, four arm bones, two thighbones, and part of a pelvis—were later salvaged by a local businessman, who, thinking they belonged to a cave bear, passed them on to a fossil collector. The fossil collector realized that he was dealing with something much stranger than a bear. He declared the remains to be traces of a “primitive member of our race.”
As it happened, this was right around the time that Darwin published On the Origin of Species, and the fragments soon got caught up in the debate over the origin of humans. Opponents of evolution insisted that they belonged to an ordinary person. One theory held that it was a Cossack who had wandered into the region in the tumult following the Napoleonic Wars. The reason the bones looked odd—Neanderthal femurs are distinctly bowed—was that the Cossack had spent too long on his horse. Another attributed the remains to a m
an with rickets: the man had been in so much pain from his disease that he’d kept his forehead perpetually tensed—hence the protruding brow ridge. (What a man with rickets and in constant pain was doing climbing into a cave was never really explained.)
Over the next decades, bones resembling those from the Neander Valley—thicker than those of modern humans, with strangely shaped skulls—were discovered at several more sites, including two in Belgium and one in France. Meanwhile, a skull that had been unearthed years earlier in Gibraltar was shown to look much like the one from Germany. Clearly, all these remains could not be explained by stories of disoriented Cossacks or rachitic spelunkers. But evolutionists, too, were perplexed by them. Neanderthals had very large skulls—larger, on average, than people today. This made it hard to fit them into an account of evolution that started with small-brained apes and led, through progressively bigger brains, up to humans. In The Descent of Man, which appeared in 1871, Darwin mentioned Neanderthals only in passing. “It must be admitted that some skulls of very high antiquity, such as the famous one of Neanderthal, are well developed and capacious,” he noted.
In 1908 a nearly complete Neanderthal skeleton was discovered in a cave near La Chapelle-aux-Saints, in southern France. The skeleton was sent to a paleontologist named Marcellin Boule, at Paris’s National Museum of Natural History. In a series of monographs, Boule invented what might be called the cartoon version of the Neanderthals—bent-kneed, hunched over, and brutish. Neanderthal bones, Boule wrote, displayed a “distinctly simian arrangement,” while the shape of their skulls indicated “the predominance of functions of a purely vegetative or bestial kind.” Boule’s conclusions were studied and then echoed by many of his contemporaries; the British anthropologist Sir Grafton Elliot Smith, for instance, described Neanderthals as walking with “a half-stooping slouch” upon “legs of a peculiarly ungraceful form.” (Smith also claimed that Neanderthals’ “unattractiveness” was “further emphasized by a shaggy covering of hair over most of the body,” although there was—and still is—no clear evidence that they were hairy.)