Neanderthals glued their stone tools into place on wooden handles, a new study suggests. Archaeologists found chemical traces of pine resin on 10 stone tools from Grotta del Fossellone and Grotta di Sant’Agostino, on the western coast of central Italy. That’s pretty solid evidence that Neanderthals living in Italy were hafting their stone tools and securing them in place with resin between 55,000 and 40,000 years ago—long before Homo sapiens set foot in Europe.

Getting a grip on stone tools

For around three million years, hominins had been shaping various cutting, pounding, and scraping tools out of stone, but something was still missing. Imagine trying to skin and butcher a deer using a knife with no handle, and you’ve got life for most of hominin history. Hafting tools was a major improvement.

Typically, hafting a stone tool involves fitting it into a notch or slot in a wooden handle; the tool-maker might then lash it into place with tightly wrapped sinews or plant fibers. But people also use tree resin or pitch as a glue to help hold the tool in place.

“Once softened, the resin is pliable and can be pushed into position in the haft and around the stone tool with a pointed stick,” wrote University of Pisa chemist Ilaria Degano and her colleagues. “The resin then sets again and hardens as it cools down, keeping the stone in place.” That’s how modern hunter-gatherers do it, and archaeological evidence suggests that humans—and Neanderthals—have been doing it for at least 200,000 years. In a previous study, a team of archaeologists identified the chemical signature of birch bark pitch on two stone flakes from a site in central Italy that had the bones of a young elephant nearby.

The stone tools from Grotta del Fossellone and Grotta di Sant’Agostino are about 150,000 years more recent than the two flakes from Capitello Quarry. But they’re quite significant, because they show us that Neanderthals in southern Europe were hafting their stone tools, and using adhesives to do it, more often than archaeologists had assumed so far. Previous studies have involved archaeologists practicing their butchery skills with stone tools, and those suggested that Paleolithic hunters would have had no need to haft their tools to get the job done. It now appears likely that the Neanderthals did not read that particular study.

Held together with resin and beeswax

We don’t have a lot of direct evidence of hafted stone tools, because wooden handles and sinew lashings tend to decay pretty quickly unless something really unusual happens. For example, a 5,300-year-old mountaineer now known as Ötzi carried hafted weapons, complete with lashings and adhesive to hold the blades in place. Thanks to the deep freeze of a glacier, those tools were found intact alongside his corpse in 1993. Burial in a peat bog can also do the trick. But so far, archaeologists haven’t gotten lucky enough to find well-preserved hafted tools dating back to the reign of the Neanderthals.

For the most part, if we want to understand when, where, and how often people started putting handles on their tools, we have to look for more subtle clues, like microscopic marks left by the haft and the lashing rubbing against the stone tool during its lifetime. Sometimes the clues are a little more obvious: visible traces of some type of residue still clung to several of the 1,000 stone tools found at Grotta del Fossellone and Grotta di Sant’Agostino.

But it's difficult to demonstrate that the sticky old residue you found on a stone tool is an ancient adhesive and not just something out of the sediment it was buried in. That’s where gas chromatography/mass spectrometry (GC/MS to its friends) comes in. By vaporizing a small sample of a substance and then separating the different compounds in the gas, GC/MS can tell you—at a sometimes dizzying level of detail—what something is made of.

The residue on 10 of the stone tools from Grotta del Fossellone and Grotta di Sant’Agostino contained compounds called diterpenes. In fact, the residues contained a particular set of diterpenes that only turn up in conifer resin. One of the samples, from Grotta del Fossellone, also contained chemicals from beeswax. Mixing beeswax with plant resin makes a stronger adhesive, and the combination has been found at other archaeological sites and among some groups of modern hunter-gatherers. And all of the samples contained chemicals like palmitic acid and stearic acid, which suggest plant oils and waxes were also part of the mix.

Neanderthals weren't stupid

The beeswax compounds, along with diterpenes from a scraper and a flake from Grotta di Sant’Agostino, showed signs that the resin had been heated. The Sant’Agostino samples contained compounds derived from methanol, which is usually given off by heated wood. That’s a perfect fit with what we know about working with resin. It tends to dry and harden when it’s exposed to air, so the Neanderthals at Grotta del Fossellone and Grotta di Sant’Agostino would have needed to heat it over a fire in order to soften it up again.

That suggests Neanderthals could start fires whenever they needed to, which is somehow still a subject of debate despite evidence that, for instance, Neanderthals in Tuscany used fire to shape and harden the ends of digging sticks 171,000 years ago. Archaeologists found traces of charcoal and an ancient fireplace at Grotta del Fossellone, in the same layer as the once-hafted tools, and both caves contained a few pieces of burnt stone.

Those fires may have been used to work on existing tools, not just haft new ones. If you re-heat the hardened resin on a hafted tool, it softens up again, and you can remove or reposition the tool. One scraper from Grotta di Sant’Agostino had pine resin residue on its scraping edge—not where you’d expect a haft to be attached. Degano and her colleagues suggest that someone used the scraper to catch melted resin while re-hafting another tool.

“We continue to find evidence that the Neanderthals were not inferior primitives but were quite capable of doing things that have traditionally only been attributed to modern humans,” said co-author Paolo Villa, adjunct curator at the University of Colorado Museum of Natural History.

PLOS ONE, 2019. DOI: 10.1371/journal.pone.0213473;(About DOIs).