The Sixth Extinction: Chapter 12 Summary & Analysis

In Germany, there is a small valley know as Das Neandertal. Here, in the mid-19th century, workers stumbled upon the first Neanderthal remains. Since then, scientists have found Neanderthal remains in other parts of Europe and the Middle East. Neanderthals had sophisticated tools, wore animal skins to keep themselves warm, and hunted for food. Then, about 30,000 years ago, they vanished. Some researchers argue that environmental changes wiped out the Neanderthals, while others claim that Homo sapiens killed them. It’s likely, however, that Homo sapiens interbred with the Neanderthals.

Kolbert visits the Max Planck Institute for Evolutionary Anthropology in Leipzig. There, she meets Svante Pääbo, the director of the department of evolutionary genetics. Pääbo pioneered “paleogenetics,” the study of ancient genetics. He hopes that, in the near future, humans will succeed in mapping the Neanderthal genome so that they can compare Homo sapiens and Neanderthal genetics side-by-side.

At first, scientists thought that the remains of Neanderthals belonged to regular human beings. However, some specialists pointed out that the bones were bowed in unusual areas. In the coming decades, more Neanderthal bones surfaced, and researchers (or sometimes amateurs) noticed that the skeletons had unusually large skulls and unusually bowed femur bones. Early 20th century scientists portrayed Neanderthals as hairy, brutish creatures who could barely stand up straight, and this was taken as evidence of their uncivilized nature. However, after World War II, anatomists re-examined Neanderthal remains and made some striking conclusions. They decided that Neanderthals didn’t walk with a slouch, weren’t hairy, and, in fact, looked striking like modern humans. There is even some evidence that Neanderthals buried their dead and planted flowers on the graves.

DNA is often considered to be a “blueprint” for the structure of a human being. A human genome consists of billions of “lines” of four chemicals (adenine, thymine, guanine, and cytosine) housed in the nucleus of a cell. After human beings die, their genomic code deteriorates quickly, which means that it’s very difficult to find any genetic information about humans (or Neanderthals) who lived in the distant past. However, scientists have succeeded in finding genetic code in Neanderthal bones. Analysis reveals that Neanderthal DNA is very similar to human DNA, with Europeans and Asians bearing more of a resemblance to Neanderthals than Africans do.

The most popular theory for how humans evolved is the “Out of Africa” hypothesis, which states that modern humans are descendants of a small population of humans who were living in African about 200,000 years ago. Most of those humans’ descendants migrated to the Middle East, followed by Europe, Asia, Australia, and the Americas. This suggests that Neanderthals were already living in Eurasia when the ancestors of modern humans traveled “Out of Africa.”

One problem with the “Out of Africa” account of Neanderthals is that, were it true, one might think that all living humans have the same genetic overlap with Neanderthals—but in fact, some people’s DNA has much more in common with Neanderthal DNA than other people’s DNA does. Scientists have proposed a slight modification to the Out of Africa theory—the “leaky-replacement hypothesis,” which states that early human beings interbred with Neanderthals when they first encountered Neanderthals in Eurasia. Furthermore, the fact that some Neanderthal DNA seems to have survived in human beings suggests that half-human, half-Neanderthal children were cared for, rather than being scorned or hated.

What makes humans human? One might suppose that the deciding factor is intelligence—but, of course, apes and primates show many signs of intelligence. Scientists have shown that primates can make inferences, solve puzzles, etc.—in some ways, apes are better than human children at solving complex puzzles. However, human children always outscore apes in tests designed to measure their ability to read social cues. Perhaps one part of what makes humans human, then, is the ability to engage in “collective problem-solving” — solving a problem by communicating with other people.

What were Neanderthals like? To begin with, it’s pretty clear that they made stone tools. It’s also likely that they buried their dead. Neanderthal remains betray signs of serious injuries, suggesting, perhaps, the “rigors of hunting” in Neanderthal society. Interestingly, there is evidence that Neanderthals were seriously injured, but then survived their injuries, implying that they took care of each other. Neanderthals spread across Europe, but it seems probable that they never built boats to cross bodies of water.

Pääbo has pioneered an intriguing theory about Neanderthals. It seems that restlessness, curiosity, and “mad ambition” are quintessential human qualities—and perhaps they’re genetic. Perhaps Neanderthals lacked these genetic qualities—they never developed the ambition to cross bodies of water, conquer territory, wipe out other species, etc.

Pääbo has found plentiful evidence of species interbreeding in human fossils. For example, in analyzing a fossilized fragment of tooth that belonged to an early, humanoid species called the Denisovans, he concluded that it is likely that humans interbred with the Denisovans. It’s possible that the Denisovans went extinct because of their low reproductive rates, and the same is true of humans’ “next-closest kin,” apes. In the 21st century, apes are going extinct because they’re not reproducing quickly enough. In a few centuries, it’s possible that humans’ “sister species”—not just Neanderthals and Denisovans, but chimpanzees, apes, etc.—will be wiped out.

Kolbert drives to La Ferrassie, a French site where the largest recorded assemblages of Neanderthal remains were discovered 100 years ago. As she watches a team of paleontologists at work, she imagines what life had been like for Neanderthals. She finds a beautiful hand-ax, almost perfectly symmetrical. When she tells a paleontologist that the ax is beautiful, he points out that Kolbert is “projecting the present” onto the past; in other words, there’s no evidence that Neanderthals designed their tools to be beautiful. Indeed, no remains of Neanderthal art or adornment have yet been discovered.

On her last day in France, Kolbert visits another archeological site, Grotte des Combarelles. There, she enters a cave where human beings once lived—on the walls, there are sketches and paintings. It occurs to Kolbert that prehistoric human beings must have been “a little bit mad” to go exploring the caves armed only with fire and axes. Perhaps if humans, with their madness, their ambition, and their “signs and symbols,” had never existed, Neanderthals would still be around.