Researchers at Eberhard Karls-Universität Tübingen and their colleagues in Germany took a closer look at the birch tar used to glue Neanderthals’ tools and found a more complex technology for creating the adhesive than previously considered.

In their paper, “The production method of Konigsu birch stump documents cumulative culture in Neanderthals,” published in Archaeological and Anthropological SciencesThe team compared different ways birch tar was formed with chemical residues found in ancient Neanderthal tools.

One characteristic of human intelligence is the ability to synthesize substances and materials not found in nature. Tool use was once part of this consideration, but as many animals have been found altering and manipulating materials for use as tools, it has become a unique marker of intelligent behaviour.

The manufacture of synthetic materials remains an important aspect of our cognitive advantage over other animals, as it requires conscious thinking, planning, and an understanding of our actions to transform raw materials through a learned process.

The Tübingen study shows that modern humans are not alone in this ability and were not the first to reach this mental milestone. The birch tar used by Neanderthals predates any known adaptation by modern humans by 100,000 years. The adhesive was used as an adhesive backing to bond stone to bone and wood in tools and weapons, with the added advantage of being waterproof and resistant to organic decomposition.

It is believed that how Neanderthals made birch tar was either a manufactured process or an existing substance that was discarded from the rock after a fire. Through a comparative chemical analysis of two pieces of birch tar from Germany and a large reference batch of birch tar made with Stone Age techniques, the researchers found that Neanderthals did not simply find birch tar after the fire, nor did they use the simplest manufacturing method.

Instead, the researchers discovered, the Neanderthals who made German birch tar used the most efficient method with an oxygen-restricted, underground heating, gradual distillation process to extract the synthetic adhesive.

According to the authors, “It is unlikely that this degree of complexity could have been invented spontaneously.” Which indicates that the technique would have started with simpler methods and developed into a more complex process by experiment.

To test the process that led to German tar, the researchers dabbled in experimental archeology by recreating five different extraction techniques, two above ground and three underground. With the birch tar extracted, the team applied infrared spectroscopy, gas chromatography-mass spectrometry, and microcomputed tomography to analyze and compare tar-making techniques with ancient birch tar artifacts.

The availability of oxygen at the time of extraction left a clear mark on the experimental tar, creating a signature that clearly separates the above-ground from the underground routes. The ancient artifacts are identical to the underground manufacturing process. Both the ancient tar artifacts and the underground experiments showed some mineral reactions in the soil and were devoid of soot-bound carbon, unlike the above-ground techniques.

Underground diversion techniques are more difficult to implement than above ground techniques because some elements cannot be noticed or corrected after the procedure has begun which requires more careful preparation.

Evidence for Neanderthals has only grown cognitively complex in recent years, as archaeological evidence reveals that many technological innovations thought to be recent human inventions were already in use among Neanderthals. At this point, it would benefit anyone who prefers to think of human intelligence as an exceptional singularity to admit that Neanderthals were also human.

According to the authors, “Tar-making by Neanderthals appears to be the first documented manifestation of this kind in human evolution.”