P. J. Texier copyright MPK/WTAP

Cutting edge. In ancient sediments near Kenya's Lake Turkana, archaeologists have found stone hand axes dating to 1.76 million years ago—the oldest examples yet found of the Acheulian stone-tool technology.

Why Did Early Humans Leave Africa Without the Latest Gadgets?

People love to get their hands on the latest and greatest technology, and scientists had long believed that early humans were no exception. Paleontologists theorized that our ancestors didn't start leaving Africa until they had developed advanced hand axes. But a new study finds that early humans began to migrate out of the continent with more primitive tools even though better technology had been invented.

Over time, various groups of ancient humans have made various types of stone tools. The oldest and most rudimentary instruments—sharp-edged stones created by banging rounded rocks against larger stone "anvils"—belong to the Oldowan culture, dating back to about 2.6 million years ago and persisting to about 1.7 million years ago. From the Oldowan, a more complex tool culture developed called the Acheulian about 1.6 million years ago. These are more complicated tools, such as teardrop-shaped hand axes, created by striking carefully selected stones with other rocks called hammerstones. These tools were useful for a wider range of tasks than the Oldowan ones. It was the Acheulian culture that first spread farthest around the globe, and it persisted until about 100,000 years ago.

Paleontologists used to think that humans didn't start leaving Africa until they had developed the advanced Acheulian tools. But recent discoveries of Oldowan tools in Dmanisi, Georgia, indicate that some of our prehistoric relatives must have left Africa with just a primitive toolkit. The new discovery, however, suggests that at least some of our African ancestors had better tools to chose from.

On the northwest shoreline of Kenya's Lake Turkana, at a site known as Kokiselei, researchers previously found both Oldowan and Acheulian tool types in the same 1.76-million-year-old sediments. The tools were located in a series of gravel, sand, and mudstone beds and included picklike tools, basic hand axes, and broken pieces of stone left behind in the tool-making process. (Just who made the tools is unclear from the archaeological evidence alone, though our relative Homo erectus is identified as the likely creator of at least the Acheulian tools.) The new research pins down a new geological date for the site.

The date pushes back the origin of the Acheulian culture by almost 200,000 years, the team reports online today in Nature. And that means that advanced hand axes had already been invented when humans first started leaving Africa, says the study's lead author, geologist Christopher Lepre of the Lamont-Doherty Earth Observatory in Palisades, New York.

"It seems that the Acheulian culture branched off from the Oldowan while the Oldowan was still being used," he says, "and both persisted contemporaneously for a period."

So why did early humans leave home without a better toolkit? That is a mystery, but it may have something to do with the way knowledge of how to make the tools was transmitted from group to group. Even though the Acheulian tools had been invented, those who made them may have perished without passing on their skills, meaning that another group may have had to reinvent the same tools thousands of years later. Likewise, because some populations were already leaving Africa, it would have taken time for the skill to spread in Africa before being carried elsewhere.

"Novelties like blade tools and bows and arrows may have been invented and reinvented many times over," and, therefore, "we cannot be sure that the tools found at Kokiselei were really the beginning of the establishment of the Acheulian," says anthropologist Chris Stringer of London's Natural History Museum, who was not involved with the study. The Kokiselei tools may have been an early experiment that did not catch on, and, if this is the case, another, later population of humans stumbled upon the same technology and more successfully transmitted that knowledge to other pockets of prehistoric people, about 1.6 million years ago. The hand ax and other Acheulian artifacts at Kokiselei may have been tools before their time.

Posted in Paleontology