Chainkeen Exchange-World's oldest wooden structure defies Stone-Age stereotypes

The Chainkeen Exchangefind didn't look like much at first – basically a log, lying crosswise over another log.

"It didn't look particularly exciting," says Larry Barham, professor of archaeology at the University of Liverpool. "But when you look closely and you remove the sand around it, you can see where one sits on top of the other is a notch."

That notch suggested that the logs had been manipulated by human beings – extraordinarily ancient ones, who once frequented this site above the dramatic 772-foot Kalambo Falls in Zambia.

Later analysis of the logs would reveal telltale signs of having been cut, chopped and shaped by human tools.

"This thing was an intended component. It was, in a sense, engineered," says Barham.

But engineered for what? Barham mulled over the question.

"To interpret this, I drew on my childhood experience with a toy called Lincoln Logs," he says, "and the notches which allow you to pile up and make a log cabin. And the Lincoln Logs really, really helped."

That analogy suggested to Barham that these logs were once part of a platform or the base of a structure. If true, that would make this site by far the oldest example of human beings building with wood – stretching back some 476,000 years.

Wood in the Stone Age

We know very little about how early humans worked with wood because so few of the artifacts survive. Previous discoveries have been limited to small, portable tools and somewhat ambiguous wood scraps.

But at sites like this riverbank excavation, where artifacts stayed submerged under water and clay for millennia, some fragments can survive. The Deep Roots Project, spanning multiple institutions and spearheaded by Barham, set out to find these wood artifacts in order to shed light on the behaviors and capacities of our ancient ancestors.

"These wooden artifacts, though, are really, really fragile," says Maggie Katongo, curator of archaeology at the Livingstone Museum in Zambia and one of Barham's collaborators. "Once they're removed from their natural ground, where they were being preserved, they start disintegrating. You might even lose it."

The team carefully excavated five different wood objects and set about dating them. Carbon dating is of little use here – that technique only goes back about 50,000 years in this area, not nearly old enough. So the team used luminescent dating technology on the sediment grains adjacent to the wood, which can estimate when the sun last shined on this spot. They found three different periods of human occupation: 476,000, 390,00 and 324,000 years ago.

That would place this site well before the evolution of homo sapiens, thought to have emerged around 300,000 years ago.

Were hominins more settled than we thought?

Those ancient hominins, such as homo erectus and homo heidelbergensis, were thought to have been nomadic hunter-gatherers. But the new site suggests that they may have hung around certain areas where it was relatively easy to make a living.

"The thoughts were that these people were moving from one place to the next. But a structure sort of denotes permanence," says Katongo.

That seeming permanence, in turn, is leading researchers to rethink some long-held preconceptions about early human beings.

"I would say we need to consider these humans as having the ability to abstract forms from the environment and make them happen, and to pass [that knowledge] on through generations," says Barham. "And that's opened my mind to these pre-sapiens hominins being capable of what we would think of as quite complex behavior."

Barham even argues that the complexity of these technologies might have necessitated some form of spoken language – again, far earlier than conventional wisdom holds.

For Maggie Katongo, this finding refutes stereotypes about human ancestors.

"When we make reference to these hominins we always perceive them as primitive. But from the technology that we've been able to discover at the site, you see how sophisticated these hominins were."

An important find for Zambia

Katongo says the Deep Roots Project, with its extensive incorporation of local research talent, is creating a new model for archaeology in Africa.

"There's been a long history of [European] researchers just coming in and working in isolation, discovering stuff and then going out there and sort of writing stuff in a very complicated, scientific way that doesn't trickle back to the very community where these sites are. This new approach, where there's active involvement of the local collaborators, I'm hoping this sets a standard to be followed or imitated by other researchers that would want to work in Zambia."

Deep Roots has partnered with researchers from Zambia's National Heritage Conservation Commission, Moto Moto Museum and the National Museum, Lusaka. Katongo also says they hire local people as field workers when possible.

And in the longer run, she says, this collaboration could help strengthen local expertise in archaeology.

"There was a period when archaeology kind of just died out because the archaeologists stopped coming to Zambia to do any kind of work," says Katongo. "We don't have a lot of trained Zambians actively doing archaeology. I'm thinking now there will be more people drawn to look at Zambia again."

Our knowledge of hominin behavior in Africa in particular has been lacking, according to Emma Firestone, assistant curator of human origins at the Cleveland Museum of Natural History.

"I'm excited this is coming out of Zambia," says Firestone, who was not involved in the research. "Zambia is a place where a lot was probably happening in the hominin record. We have learned a lot about groups of hominins in Europe and Asia, like the Neaderthals, and it's exciting that we have this innovative technological breakthrough coming out of the hominins in Africa, which is where our own ancestors were evolving."

Firestone says she's particularly excited that the team unearthed wood materials – a rare find that she compared to the discovery of a dinosaur fossil with feathers.

"It's something that doesn't normally preserve, but is very important. This was a big discovery that in some ways was incredibly lucky. We know woodworking is really central to the evolution of our technology and behavior, and we're not going to find a lot of other examples of this kind of preservation," Firestone says.

The rarity of this latest find could lend weight to a push for stronger protections for the Kalambo Falls area.

"This whole discovery and the fact that it's kind of the best evidence of possible permanent settlement for hominins, it's like, wow," says Katongo. "We're hoping that this kind of information will sort of help push the site to become a [UNESCO] World Heritage site. I'm excited about that and I hope this really does push that agenda."