Since long before the oldest physical creations in human culture--the raising of the step pyramid at Saqqara or the Great Wall of China, for example--people have been telling stories of human origins. Through religion, such explanations have become creation myths, sacred genealogies, epic tales, and pious platitudes (e.g., "you are a child of God").
With the publication of Charles Darwin's The Descent of Man in 1871, a rival explanation took shape. We are animals, it said, of the genus Homo, which split from Pan (chimpanzees) some seven million years ago and wandered through a hominin lineage that walked upright, made use of fire, lost its brow ridge and body hair, and at long last became us: members of the uniquely communicative, collaborative, and inventive species Homo sapiens sapiens--the doubly wise ones.
But does science have its story straight?
Typically, as science advances, uncertainty shrinks. In recent years, however, the scientific narrative of our origins has grown increasingly hazy. Consensus on the date of the human-chimpanzee split has shattered. Some have pushed the date back to as much as thirteen million years ago; others have reeled it in to six million years, and a much cited 2006 article in the journal Nature claims genetic evidence for repeated episodes of interbreeding rather than any definitive split.
The post-split tracks have also been muddied. Early anthropologists conceived of an evolutionary lineage leading to modern humans. We have since learned that many kinds of hominin have walked the earth. Some, like the Neanderthals and the recently discovered Denisovans, both competed and interbred with our ancestors before falling to the scythe of natural selection. Others like Homo floresiensis, better known as "the Hobbit" species, remain an enigma.
Now, an astonishing find in the Rising Star caverns of South Africa has touched off an explosion of new questions and controversies.
In a nearly inaccessible chamber at the back of a tortuous cave system, a mysterious trove of fossils lay undisturbed for unknown ages, until a couple of cavers found it in 2013.
"It is the most significant and extensive discovery of early human ... fossils ever made on the continent of Africa," Lee Berger, head of the team that found them, told British television. He's not exaggerating. So far fifteen nearly complete individuals of an entirely new hominin species have been recovered. More than 1,500 fossils have come out of the chamber, and no one knows how many more remain to be discovered. The fossil remains span all ages, with peaks among the elderly and the very young.
All the fossils are similar to each other and different from other known hominin species. Like a child's split-page flipbook, they combine some human-like features with some very apelike features.
Homo naledi (named after the cave where it was found) has humanlike hands and feet and facial features approaching ours, but has a small head and an apelike trunk. Its fingers are more curved than a modern human's and its shoulders more rounded, indicating that it was a climber. However, its feet are nearly identical to ours, suggesting that it was also an accomplished upright walker. This pattern holds down to the smallest details.
"When you look at those teeth, you realize that they are not [from] modern humans," paleoanthropologist Charles Musiba of the University of Colorado-Denver said in a televised interview. "They have some features transitional between modern humans and some of our earliest ancestors."
The most astonishing aspect of the find, however, is not anatomical but implicit. The space where the fossils lay appears to be a burial vault. All the evidence suggests that these primitive creatures with brains the size of an orange took pains to haul their dead through the cave and deposit them in what is now called the Dinaledi Chamber ("chamber of stars").
The discovery of Homo naledi has been hailed as a "missing link" and scorned as a triumph of showmanship over science. But most of all, it has rekindled that eternal question: who are we?
The tale of discovery has been told--and shown--but it bears a brief retelling. In 2013, two slim and brave South Africans were scouting one of many unexplored caverns near the Cradle of Humankind, a World Heritage Site northwest of Johannesburg, in a region that has produced more than a third of all discovered ancestral fossils.
Having scaled a wall at what he thought was the back of the cave, Rick Hunter shifted to make room for his partner, Steve Tucker. Suddenly, like Alice, Rick slithered down a hole into a wonderland. The narrow, twisting passage led to a hidden chamber littered with fossils--hominin fossils, whole hominin fossils, and almost nothing but hominin fossils. (Note: "hominin" is a recent term that denotes a strictly human ancestral lineage, as distinguished from the larger family of closely related primates that includes chimps, orangutans, and gorillas, whose ancestral members are termed "hominids.")
Fortunately, when Hunter dropped into the unsuspected grotto, he had a helmet camera running. Hunter was part of a network of amateur explorers who were paid to report any promising finds to the aforemetioned Berger, (pictured below), an American paleontologist based at South Africa's...