How did modern humans take over the planet? It's one of the most intriguing questions in science.
Right now, sitting pretty at the top of the food chain, it's tempting to see our 200,000-year rise to power since the emergence of the first Homo sapiens as a given - as the evolutionary endpoint of a story that got started on the African savannah via two key innovations: bigger brains, and the shift to walking upright.
Yet for our ancestors, things were not so clear-cut. They were not (as we now find ourselves) the only game in town. When the Cro-Magnons (ancestors of modern humans) migrated north from Africa's Rift Valley to settle Europe around 40,000 years ago, the latter continent was already populated by another breed of hominid, the Neanderthals. Within a few thousands years, the Neanderthals were wiped out, and the Cro-Magnon had taken over.
Why was this? What special attributes did our ancestors possess that the Neanderthals did not?
As Ian Tattersall, curator of anthropology at the American Museum of Natural History, points out, the fossil record often delivers more questions than answers. Neanderthal skeletons, for example, show that Neanderthals had stronger builds and the same-size brains as Cro-Magnons. They were sophisticated toolmakers. Animal remains found at Neanderthal sites reveal they were skilled hunters, experts in bringing down large prey such as woolly mammoths. Based on this evidence, there is no obvious reason why we made it, and they did not.
But Tattersall says he thinks we need to look beyond the fossil record to find the secret to our success. One place to start looking, he says, is in the Lascaux caves in southern France. Discovered accidentally in 1940 by four children, the Lascaux cave complex contains hundreds of paintings of animal figures in caverns larger than football fields.
Talking at the museum this week to promote his new book, “Masters of the Planet: The Search for Human Origins,” Tattersall describes a visit to the caves as “one of the most profound experiences of my life.” It's more than just the beauty of the paleolithic art that moved him, however. The cave paintings, he says, prove early man's ability to think symbolically. Horses drawn on to the cave walls are symbolic representations of real-life horses.
No other species of early humans left artwork behind, which, he says, is the crucial difference.
The capacity for abstract thinking is the key to our success. All our creativity stems from it. But abstract thinking is not only useful for making art. Early hunters, for example, reporting back on the movement of reindeer herds, would be disadvantaged if those hearing the report could not make the mental leap of faith needed to understand that these herds existed even though they had not seen them.
“It is this capacity for 'what if' thinking that sets humans apart from all other creatures,” Tattersall says.
He says it's no coincidence that this advance in human cognition came along at the same time as language. “Symbolic thinking is impossible to imagine without language,” he says.
There is no evidence to tell us whether Cro-Magnons spoke in a language with each other, although Tattersall says he's certain they did. It's also impossible to say if early humans developed linguistic ability, or if it were innate, as acclaimed linguist Noam Chomsky has argued. Chomsky believes humans are born with an ability to learn oral language. Hence, toddlers have amazing talent for stringing words together in the proper order even though they may never have heard the sentences before.
According to Tattersall, humans may have possessed the ability for language for millions of years before some, as yet unknown, cultural stimulus set it in motion.
“Birds had feathers for millions of years before they learned to fly. You acquire a feature and, much later on, you find a use for it,” says Tattersall, who has been researching our history through the fossil record since the 1960s and has written several books on the subject.
Of course, the capacity for symbolic thought is just one theory of how humans got to the top of the food chain, and there are many others.
It may have been, as some anthropologists have argued, that in a prehistoric age where nature was red in tooth and claw and fearsome predators such as saber-toothed tigers roamed the landscape, our ancestors were simply the most efficient at killing off the competition. Disease or drought may have played a part; so too may have historical climate changes.
That humans' unique way of seeing the world helped them on their rise to becoming the masters of the planet seems indisputable, however. Whether it was the one, big thing that made all the difference, we may never know.