Paleolithic technology and the boom in cultural evolution
About 300,000 years ago something happened that was unlike anything in the previous few billion years, something that would have ever-expanding repercussions.
Stanley Kubrick presented his view of this moment in "2001: A Space Odyssey." An ape realizes the awesome potential of the bone in his hands. Hurled into the sky, the bone morphs into a space station.
Meanwhile, Pope John Paul II, in his 1996 Statement on Evolution, said the turning point was when God intervened and divinely injected the soul into the Neanderthals and prehumans. (Incidentally, this Statement is also where the Pope admitted that "evolution is more than a hypothesis.")
Kubrick was closer to what scientists believe kick-started modern human evolution: the Paleolithic discovery of technology.
Stanley Ambrose, a paleo-anthropologist at the University of Illinois, sets out the evidence for tool-making and the evolution of hands and brains in the March 2 issue of the journal Science. His review explains what happened in the time between an ape ancestor with a bone and an ape descendent working on the international space station.
Chimpanzees have a variety of tool-making and using behaviors, so we can assume that tool-use by our last common ancestor was comparable to chimps. Bipedal locomotion was achieved on the African savanna about 4.2 million years ago, but was not accompanied by tool-use. Australopithecus (of which "Lucy" is the most famous example), lived about 3 million years ago but is not thought to have used tools.
The first evidence of technology in the genus Homo (the descendents of Australopithecus) comes 2.5 million years ago, from the Ethiopian Rift Valley. These early hominids used slivers and lumps of stone; bones with hammer marks suggest that the tools were used for butchery and marrow extraction. Although the tools are simple, they required far greater manual skills than modern chimps have.
Chimps move their arms mainly from the shoulder, and their wrist is immobile. Chimps' wrists lock, to facilitate knuckle-walking. Hominids, walking upright, could develop a mobile wrist - and use it to make stone tools, manipulate small tools... and throw fastballs.
Meat-eating has been considered as the force driving tool-use, but microwear polishes on stone flakes show that they were used for cutting and scraping wood, for cutting reeds and sedges, as well as for cutting meat. Early technology opened the door to high-quality food resources, which could fuel the energy demands of the early Homo with her large brain. (Female chimps show greater skill and persistence in tool-use, suggesting that females played a leading role in technological evolution.)
Homo habilis, with its large brain (600-800 cc compared to 450-500 cc for Australopithecus and chimps), made a major breakthrough. It was able to steady an object in one hand and work it with a tool held in the other.
Hand-axe made by the large-brained
Homo erectus about 1.5 million years ago.
FIGURE COURTESY OF STANLEY AMBROSE
Homo erectus, coming later, manufactured large cutting tools that required preconceived design. By about 1.5 million years ago hominids systematically used fire, and discoveries in Germany show that by 400,000 years ago our ancestors there were making wooden javelins (Vorsprung durch Technik, progress through technology, as their descendents would later say).
But technological and cultural evolution really accelerated from about 300,000 years ago. The Neanderthals and the early humans made stone-tipped knives and spears, and scrapers mounted in wooden handles.
"The increase in technological complexity may be analogous to the difference between primate vocalizations and human speech." says Ambrose. The construction of composite tools (say an ax with a wooden handle and a stone blade bound with vine) involves nonrepetitive, hierarchical actions, in the same way that grammatical language requires a hierarchical sequence of sounds in order to create a meaningful phrase. And both speech and composite tool manufacture are controlled by adjacent parts of the brain, known as Bronca's area.
"If composite tool manufacture and grammatical language coevolved about 300,000 years ago, then Neanderthals and modern humans could speak," said Ambrose. The claim is supported by reconstruction of fossil hominid vocal tracts.
"The complex problem-solving and planning demanded by composite tool manufacture may have influenced the evolution of the frontal lobe," said Ambrose.
For millions of years our ancestors only grunted on the plains of Africa, but when humans developed near-modern brain size, anatomy and grammatical language, cultural evolution took off in a self-reinforcing, ever-faster spiral.
"A mere 12,000 years separate the first bow and arrow from the International Space Station," said Ambrose.
Early humans and Neanderthals had technology and perhaps conversation. But the question gripping the paleontology community at the moment is: Did they do it?
When modern humans got to Europe 40,000 years ago, they found Neanderthals already there. They lived side by side for several thousand years. Our technologies were the same, we hunted the same animals and ate the same plants. Both groups buried their dead.
"I think that one thing that was going on was sex," says Fred Smith, a paleoanthropologist at Northern Illinois University.
The best evidence comes from the bones of a 4-year-old boy buried about 24,500 years ago in Portugal. The skeleton combines features of Neanderthals - short arms and broad trunk - with those of modern humans, such as a strong chin and a pubic bone. The mix convinced Erik Trinkaus of Washington University that interbreeding went on for generations.
"This is not one Neanderthal and one modern human making whoopee in the bushes." he told Time magazine.
And yet mitochondrial DNA extracted from Neanderthal bones is quite different from modern humans, suggesting that moderns replaced Neanderthals without interbreeding. The question is unresolved, so novelists like Jean Auel can continue to write raunchy tales of rough Neanderthals and delicate modern humans and at least have some scientists on their side.E-mail Rowan Hooper at firstname.lastname@example.org