Ancient humans were building large wooden structures – possibly houses – almost half a million years ago. The discovery, the earliest evidence of wooden construction, suggests that some ancient communities were far less nomadic than we have assumed.
“These people were behaving in ways I hadn’t expected,” says Larry Barham at the University of Liverpool, UK. “It’s a disruptive discovery.”
Barham and his colleagues uncovered the evidence at Kalambo Falls, an archaeological site in Zambia. In 2019, they spent a month excavating a sandbar some 300 metres upstream of the falls.
One of the first artefacts they found was a wooden tool, probably a digging stick. “The number of sites where wood is preserved is small,” says researcher Geoff Duller at Aberystwyth University, UK.
As they continued to dig, they made another discovery: a 1.4-metre-long log overlying an even larger log that was too big to fully excavate during their month-long project. They saw that the overlying log had been worked with tools to fashion a deep notch midway along its length. This allowed it to interlock with the underlying log at a 75-degree angle, creating a relatively sturdy joint. The researchers speculate that the two interlocking logs were once part of a larger wooden structure.
Duller then dated the artefacts using a technique called post-infrared infrared stimulated luminescence. This involves measuring the time since the mineral grains in the sand that surrounded the wood were last exposed to light prior to their burial. The mineral grains – and the artefacts they surround – were buried about 476,000 years ago, which implies that the wooden structure was built before our species evolved. The engineers therefore belonged to an earlier human species, possibly Homo heidelbergensis.
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We already knew that ancient humans made use of wood. For instance, researchers have discovered 300,000-year-old wooden spears at a site in Germany, possibly made by H. heidelbergensis. “But those wooden implements are portable,” says Barham, which fits with the prevailing idea that early humans were always on the move. The large wooden structure at Kalambo Falls suggests to Barham that at least some early humans were staying put and choosing to enhance their environment. “They were investing in this place.”
“There’s something really exciting about this discovery that they were constructing and [they] had a real sense of the importance of place,” says Penny Bickle at the University of York, UK.
The ability to modify the local environment – sometimes called niche construction – isn’t uniquely human. Plenty of other species, such as beavers, do this too, but their techniques are far less sophisticated than those used at Kalambo Falls. “To my knowledge, [non-human] animals do not use tools to modify materials to create structures,” says Annemieke Milks at the University of Reading, UK.
The engineers at Kalambo Falls needed to produce sharp-edged stone tools from rocks, recognise they could use those tools to cut through wood and then work in groups to transport and modify that wood to produce a large structure. “It involved a lot of planning and I do think language was involved” says Barham.
However, it is difficult to say exactly what sort of wooden structure the logs once belonged to. Barham speculates it might have been a dwelling or maybe a wooden walkway raised above the wet floodplain designed to keep early humans, and their food, dry. Manuel Domínguez-Rodrigo at Rice University in Texas says that, while it may have been a structure or shelter, we can’t read too much into the function of just two pieces of wood.
In an accompanying opinion article, Milks says that the finding shows “when people started to structurally alter the planet for their own benefit”, arguably drawing a line between Kalambo Falls and today’s highly modified human environments.
But Barham thinks the story is more complicated. He says there were periods after the Kalambo Falls structure was built when humans were typically more mobile – meaning there isn’t a direct link between the apparently sedentary behaviour on show at Kalambo Falls and the sedentary human lifestyles of recent millennia.
Either way, the discovery should shift perceptions, says Barham, because it gives us a rare insight into just how important wood must have been to ancient humans. “We might need to rethink our labelling of the Stone Age,” he says. “Maybe it was more of a wood age.”