Neanderthals May Have Invented Glue, but That Doesn’t Mean They Were Smart

They may have been as smart as us, or not, but using burned resin to haft weapons turns out not to have been complex process: take bark, add fire on a rock and wait

Ruth Schuster
Ruth Schuster
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An exhibit shows the life of a neanderthal family in a cave in the new Neanderthal Museum in the northern town of Krapina,February 25, 2010.
An exhibit shows the life of a neanderthal family in a cave in the new Neanderthal Museum in the northern town of Krapina,February 25, 2010. Credit: REUTERS
Ruth Schuster
Ruth Schuster

Were Neanderthals “just like us” or not? The pendulum of the “Noble Neanderthal” as opposed to brute has been swinging wildly in recent years, and it just swung backwards. Recently the argument arose that Neanderthal use of birch tar to haft stone tools indicated control of fire and advanced technology. Now a new paper published in PNAS argues that Neanderthal use of tar made from trees as glue doesn’t necessarily prove they had advanced techniques after all. They may have, but gluing their weapons with birch tar isn’t the indicator, claims the paper by Patrick Schmidt of the University of Tübingen and others.

Hafting in this context means to attach stone tools – axes and spearheads and the like – to a haft made of wood or bone. Think how much more effective an ax with a handle is, compared with an ax without a handle. Imagine trying to cut down a tree using an ax without a handle.

Maybe the Neanderthals really did invent glue. Maybe not. Either way, the oldest known evidence of hafting with glue was found in 2005 in Campitello Quarry, central Italy, around 200,000 years ago. The hominins there, probably Neanderthals, were using birch-bark tar to affix stone tools to handles. The dating is based on the fossil voles found at the site. The relevant findings in the quarry were meager: two stone flakes partially covered in birch-bark tar, but they sufficed. 

In June, a new paper published in Science Daily reported finding more Neanderthal tools hafted using birch-bark tar in two coastal caves in Italy, del Fossellone and di Sant’Agostino. These dated to the Middle Paleolithic, 55,000 to 40,000 years ago.

“Other evidence of hafting and adhesive use by Neanderthals shows that they were using adhesives on a wide number of tools – scrapers, knives, spear points,” Paul Kozowyk of the University of Leiden, who conducted a separate study on Neanderthal gluing habits, tells Haaretz.

“Tar could be used to fix the stone tool to a wooden handle (such as for a spear) or simply to create a protective back to the flake, making it easier and safer to hold,” he added. 

The reconstruction of a Homo neanderthalensis, who lived within Eurasia from circa 400,000 until 40,000 years ago, is seen in a modern business suit at the Neanderthal Museum in Mettmann, Germany, JulCredit: Martin Meissner,AP

How much of an achievement is this gluing activity? The question boils down to how tar adhesive was made tens and hundreds of thousands of years ago. A study from 2017 by Kozowyk and his colleagues published in Scientific Reports experimented with birch tar production and concluded that making substantial amounts of useful tar glue required advanced techniques and anaerobic conditions: firing in a closed environment such as a clay castle, ash mount, or ceramic container.

All it took was a tree, an open fire on a rock and some patience, rebuts Schmidt.

Blunt-force trauma and dinner

Stone tools go back more than 3.3 million years, halfway through the saga of Homo sapiens’ evolution, and evidence of hafting also predates sapiens-kind itself. Certainly, hunting large game does. While our earliest ancestors were evidently vegetarian (as gorillas are too today), meat-eating began millions of years ago. Australopithecines who lived about four to two million years ago were omnivorous, and clear evidence of big-animal hunting – a deer – has been found from 780,000 years ago in Gesher Benot Yakov in Israel. At some point early types of humans figured out that killing with a sharp stone spear is a lot more efficient than hunting by blunt-force trauma.

It bears adding that there is still no consensus on whether Neanderthals could control fire, meaning whether they could deliberately ignite it, as opposed to helping themselves to convenient bushfires. It also bears stating that controlling fire temperature and manipulating adhesive properties requires advanced mental traits. So one question was how sensitive the tar production process is.

A birch tree. Credit: Andreas Lakso

Kozowyk published the results of three experiments making tar from birch bark, in anaerobic conditions but without using ceramics, which the Neanderthals didn’t have. They concluded that the Neanderthals had to have been able to recognize “material properties, such as adhesive tack and viscosity” and to have further finessed the technology in order to achieve the quantities of tar found in the Middle Paleolithic archaeological record.

“A simple bark roll in hot ashes can produce enough tar to haft a small tool,” Kozowyk concluded. Kozowyk and his team even postulate that Neanderthals invented the process after noticing tar in partially burned bark rolls; then they might have learned to regulate the temperature of the fire and improve their yield.

Schmidt and his team argued in 2019 against the theory that the mere use of the tar indicates Neanderthal behavioral complexity. Since producing tar, involving burning rolls of bark under anaerobic conditions, was assumed to require a “cognitively demanding setup.” Therefore, its production was considered to be of the earliest manifestations of modern cultural behavior. 

But Schmidt and his team managed to make birch tar by burning the bark on a rock in the open air. When the bark is burned next to a hard surface such as rock, which is normally where it would have been burned, birch tar ensues and can be easily scraped off the rock. This ordinary process produces usable quantities of tar in a single session. Chemical analysis of the tar deemed it similar to the ancient tar, and mechanical tests showed it was suitable for hafting.

So, as Neanderthals had rocks and could use fire, in addition to the fact that birch grows in Europe, and the process did not require special smarts, Schmidt and the team conclude that the presence of birch tar alone cannot reflect on Neanderthal cognition or culture.

Kozowyk begs to differ. “I don’t believe that it ‘closes the case’ at all about Neanderthal glue,” he tells Haaretz. He believes that tar could initially have been discovered (and re-discovered) by very simple methods such as by examining a partially burned roll of birch bark, which was probably commonly used for starting fires. Maybe that is indeed how the glue was discovered for the first time – a Neanderthal noticed stick black goo on his birch-bark matchstick. However, this simple method just doesn’t provide much tar.

“I would suspect that to make the quantities of tar found at sites like Campitello and Konigsaue, Neanderthals already had a more efficient way of making tar,” Kozowyk argues. “Further, the idea more than 200,000 years ago to recognize this sticky substance, to figure out how it got there, and then to repeat the process for hours to make enough tar to collect and glue a multi-component tool together, still shows remarkable determination and forethought by Neanderthals!”