Arrow glue from the Neanderthal

Fifty thousand years ago, a Neanderthal living in northwestern Europe applied sticky birch tar to the back of a sharp flint splinter to make the tool easier to grip. Eventually, this tool washed down the Rhine or Meuse rivers and out into the North Sea. In the 21st century, dredgers scooped it up along with tons of sand, other stone tools, and fossilized bones, and then dumped the whole pile on the beach at Zandmotor in the Netherlands.

Despite all this, the birch tar still clung to the splinter, and it shows that Neanderthals used complex technology to make elaborate tools.

Birch tar

The production of birch tar is a rather complex process. It requires several steps, a lot of planning, and detailed knowledge of the materials and the process. The fact that archaeologists have found a handful of tools glued with birch tar shows us that Neanderthals were quite up to date.

The production of birch tar glue for tools was so routine that Neanderthals would even use it for a simple household tool like a small splinter—surviving even in the extreme Ice Age environment of northwestern Europe, in the shadow of glaciers at the northern edge of the Neanderthal world. And all the while, they used quite advanced methods for more efficient production.

There's not much room to discuss Neanderthal intelligence, given the evidence that they used fire and created art. However, a technology like making tar glue—just one component of a complex, multi-part tool—requires more than just the brain. Anthropologists typically assume that such technologies require a larger, relatively social population. Hunter-gatherers could still manage, but they would have to live in larger groups and move less than the archaeological record for Neanderthals suggests.

As far as we know, Neanderthals lived in relatively small groups with a sparse population scattered across the Eurasian landscape. Due to the shape of their femurs, they walked much more than modern hunter-gatherers. Most anthropologists wouldn't expect them to be capable of developing a technology as complex as pottery or metallurgy. But it now appears that they did.

High-tech and efficient

When experts examined the thick, black tar with a micro-CT scan, they noticed fine grains of charcoal, sand, and iron oxide mixed with the tar. These impurities were mixed very evenly, as if they had been incorporated into the tar as it melted and flowed. To achieve this kind of thorough mixing, birch tar would have to reach temperatures of 350°C or more. The amounts of chemical compounds like botulinum and lupeol in the tar also suggest a temperature in this range. To make the tar this hot, Neanderthals must have used relatively high technology to produce it.

As a study earlier this year showed, it's really not that difficult to make birch bark tar. Burning a roll of birch bark next to a flat rock will do the trick. But that's also a super inefficient way to make tar. Scientists who have tried their hand at tar production for precisely these reasons estimate that it would have taken 10 hours to make enough tar to fix just a single spike. If Neanderthals wanted to go to the trouble of putting tar on a small, everyday household tool like a splinter, then making tar in usable quantities must have been routine. And that means they probably found a more efficient way to do it.

The most efficient way to extract tar from birch bark is to heat the bark roll in a clay pot buried in a mound of earth. It's a more complicated process, requiring more steps, more planning, and more detailed technical knowledge, but it also produces more tar faster and requires about 40 times less bark for the same amount of tar. It's also the only method that produces temperatures hot enough to account for the fine grains of sand and charcoal mixed with the tar (360°C in the pot and 310°C in the bark roll).

Early inventors

The find at the Dutch Zandmotor suggests that Neanderthals used Stone Age high-tech to produce adhesives for their multi-part tools. It was a complex process, collecting and heating birch bark to extract the tar, and then using the tar to adhere a tool or form a handle.