For a while, experts assumed that our ancient human counterparts, the Neanderthals, were less advanced and intelligent than we were. But a study recently published in Science Advances is calling this long-held notion into question, reporting evidence of Neanderthals using adhesive material. That is to say, they were making glue.

“Compound adhesives are considered to be among the first expressions of the modern cognitive processes that are still active today,” said Patrick Schmidt, who co-led the study and works in the University of Tübingen’s Early Prehistory and Quaternary Ecology section, in the press release. “What our study shows is that early Homo sapiens in Africa and Neanderthals in Europe had similar thought patterns.”

Researching Ancient Tools

Glue might not seem like a novel advancement. But there is a complex chemistry that goes behind attaching a stone to a stick.

In the recent study, researchers analyzed tools over 40,000 years old from formerly unexamined collections at the Museum of Prehistory and Ancient History in Berlin, Germany. Wrapped since the 1960s, the items, and their delicate organic components, were well-preserved. On stone blades and scrapers, the team found a mix of ochre and bitumen – minerals that both occur naturally in soil and rock. 

“We were surprised that the ochre content was more than 50 percent,” said Schmidt. “This is because air-dried bitumen can be used unaltered as an adhesive but loses its adhesive properties when such large proportions of ochre are added.” 

Read More: What Types of Tools Did Neanderthals Use and Develop?

Neanderthals and Glue

Why would Neanderthals make tools with less sticky components? The team believes that they took advantage of some nifty material properties. Bitumen in liquid form is unwieldy and hard to process into a malleable material. But by adding ochre, Neanderthal hands could shape it into a solid, sticky mass. 

The team believes that the ancient hominids used these properties to craft the perfect glue: just adhesive enough to bind a stone implement to a wooden handle but not too sticky to prevent one from easily putting it down. The team ran physical tests to measure tensile strength, finding that a mixture of 55 percent ochre produces optimal ergonomics.

Close examination of the tools themselves revealed patterns of microscopic wear and tear patterns, suggesting hominid hands used them as a handle or grip.

“The tools showed two kinds of wear: one is the typical polish on the sharp edges that is generally caused by working other materials,” said Radu Iovita, an associate professor at New York University’s Center for the Study of Human Origins who ran the analysis. “The other is a bright polish distributed over the presumed hand-held part, which we interpreted as the results of abrasion from the ochre due to movement of the tool within the grip.”

Read More: 20 Things You Didn’t Know About … Neanderthals

Evidence of Advanced Tool Making

Other archeological findings observed the use of adhesives like tree resin and the aforementioned ochre from ancient human communities in Africa. However, these recent findings demonstrate for the first time that the European Neanderthals were also experimenting with more advanced tool use.

In fact, these glue-bound neanderthal tools, coming from an age called the Moustian spanning 120,000 years to 40,000 years ago, represent the oldest evidence of complex adhesives on the continent. And the team says it’s likely that the tools’ creators made great treks to find enough geographically distant ochre and bitumen for their instruments, further bolstering the case for an advanced, thoughtful design process.

Read More: Neanderthals Also Had Superior Toolmaking Abilities, Not Just Humans

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