Thanks to recent discoveries that they were canny hunters, clever toolmakers, and probably endowed with the gift of language, Neanderthals have overcome some of the nastier calumnies hurled at them, especially that they were the "dumb brutes of the North," as evolutionary ecologist Clive Finlayson describes their popular image. But they have never managed to shake the charge that their extinction 30,000 years ago, when our subspecies of Homo sapiens replaced them in their European home, was their own dumb fault. Modern humans mounted a genocidal assault on them, goes one explanation, triumphing through superior skills. Moderns drove them into extinction through greater evolutionary fitness, says another, especially the moderns' greater intelligence or social advances like the sexual division of labor. (Click here to follow Sharon Begley).

Winners—of prehistory no less than history—get to write the textbooks. So it is no surprise that we, the children of the humans who replaced Neanderthals, "portray ourselves in the role of victors and reduce the rest [of the human lineage] to the lower echelons of vanquished," Finlayson writes. "To accept our existence as the product of chance requires a large dose of humility." But in a provocative new book, The Humans Who Went Extinct: Why Neanderthals Died Out and We Survived, he argues that chance is precisely what got us here. "A slight change of fortunes and the descendants of the Neanderthals would today be debating the demise of those other people that lived long ago," he argues.

Evolutionary biologists have long recognized the role serendipity plays in which species thrive and which wither on the Darwinian vine. Without the asteroid impact 65 million years ago, for instance, mammals would not have spread so soon into almost every ecological niche on Earth (dinosaurs were in the way). Yet when the subject strikes as close to home as why our ancestors survived and Neanderthals did not, scientists have resisted giving chance a starring role, preferring to credit the superiority of ancient H. sapiens. Both are descendants of Homo erectus: some spread across Eurasia beginning 1.8 million years ago and evolved into Neanderthal by 300,000 years ago, and others evolved in Africa, becoming anatomically modern by 200,000 years ago and reaching Europe some 45,000 years ago.

These arrivistes are often portrayed as technologically and culturally more advanced, with their bone and ivory (not just stone) tools and weapons, their jewelry making and cave painting—the last two evidence of symbolic thought. Finlayson has his doubts. Neanderthals may have painted, too (but on perishable surfaces); they were no slouches as toolmakers; and studies of their DNA show they had the same genes for speech that we do. "They survived for nearly 300,000 years," Finlayson says by phone from Gibraltar, where he is director of the Gibraltar Museum. "That modern humans got to Australia before they penetrated Europe suggests that Neanderthals held them off for millennia. That suggests they weren't that backward."

Instead, moderns were very, very lucky—so lucky that Finlayson calls what happened "survival of the weakest." About 30,000 years ago, the vast forests of Eurasia began to retreat, leaving treeless steppes and tundra and forcing forest animals to disperse over vast distances. Because they evolved in the warm climate of Africa before spreading into Europe, modern humans had a body like marathon runners, adapted to track prey over such distances. But Neanderthals were built like wrestlers. That was great for ambush hunting, which they practiced in the once ubiquitous forests, but a handicap on the steppes, where endurance mattered more. This is the luck part: the open, African type of terrain in which modern humans evolved their less-muscled, more-slender body type "subsequently expanded so greatly" in Europe, writes Finlayson. And that was "pure chance."

Because Neanderthals were not adept at tracking herds on the tundra, they had to retreat with the receding woodlands. They made their last stand where pockets of woodland survived, including in a cave in the Rock of Gibraltar. There, Finlayson and colleagues discovered in 2005, Neanderthals held on at least 2,000 years later than anywhere else before going extinct, victims of bad luck more than any evolutionary failings, let alone any inherent superiority of their successors.

Sharon Begley is NEWSWEEK's science editor and author of The Plastic Mind: New science reveals our extraordinary potential to transform ourselves  and Train Your Mind, Change Your Brain: How a New Science Reveals Our Extraordinary Potential to Transform Ourselves .

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