Archaeologists have unearthed crystals at several sites containing Homo remains, suggesting that early human relatives deliberately collected these unusual stones as early as 780,000 years ago. What makes this behavior so interesting is that the crystals were not used as tools, weapons, or jewelry. Then why were they considered worth keeping?
A new study was published in boundaries in psychology Provides one possible answer. Researchers in Spain discovered why crystals are so attractive by studying how one of our closest living relatives, chimpanzees, react to them. His experiments suggest that the attraction to crystals may have deep evolutionary origins that predate modern humans.
“We show that cultured chimpanzees can distinguish crystals from other stones,” said lead author Professor Juan Manuel García-Ruiz, Ikerbask Research Professor on Crystallography at the Donostia International Physics Center in San Sebastian. “We were pleasantly surprised by how strong and natural the chimpanzees’ attraction to crystals seemed. This suggests that sensitivity to such objects may have deep evolutionary roots.”
Chimpanzees show unexpected attraction to crystals
Humans and chimpanzees diverged from a common ancestor six to seven million years ago, and the two species still share many behavioral and genetic traits. To test whether attraction to crystals might be one of them, researchers gave two groups of chimpanzees cultured at the Renfer Foundation access to crystals. The first group consisted of Manuela, Guillermo, Yvan, Yaqui and Toti. The second group consisted of Gombe, Lulu, Pascual and Sandy.
In the first experiment, researchers placed a large crystal next to a regular rock of similar size, known as a monolith. Both objects initially attracted the chimpanzees’ attention, but the crystal soon became the clear favorite while the ordinary rock was largely ignored.
After taking the crystal from the platform, the chimpanzee carefully examined it by rotating and tilting it to view it from different angles. One chimpanzee, Yvan, eventually picked up Crystal and deliberately carried her back to the dormitory.
The researchers found that the animals’ curiosity was strongest immediately after encountering the crystals and gradually died down over time, a pattern similar to the way novelty wears off in humans. The caretakers later had to trade bananas and yogurt to convince the chimpanzees to return the crystals.
Chimps quickly extracted crystals from ordinary stones
A second experiment tested whether chimpanzees could recognize small quartz crystals similar in size to those collected by ancient hominins. The crystals were picked out within a few seconds by mixing them into a pile of 20 round pebbles.
Even after the researchers added pyrite and calcite crystals, each of which were a different shape from the quartz, the chimpanzees still recognized and chose the crystal type of stones.
“The chimpanzees began to study the transparency of the crystals with extreme curiosity, holding them up to eye level and looking at them,” García-Ruiz said.
The animals continued examining the crystals for hours.
One chimpanzee named Sandy displayed particularly interesting behavior. She took both the pebbles and the crystals in her mouth and carried them to a wooden platform, where she divided them into different groups.
“They isolated three types of crystals, which themselves differed in transparency, symmetry and brightness. This ability to recognize crystals despite the differences surprised us,” García-Ruiz said.
Chimpanzees do not generally carry objects in their mouths, so researchers suggest that Sandy may have been hiding the crystals, behavior that may indicate she considered them valuable.
What might crystals have meant to early humans?
The study did not investigate whether some chimpanzees were naturally more interested in crystals than others, although the researchers say differences in personality should be considered in future work.
García-Ruiz explains, “There are Don Quixotes and Sanchos: idealists and pragmatists. Some may find the transparency of crystals attractive, while others are interested in their smell and whether they are edible.”
The researchers also noted that the chimpanzees in this study are accustomed to being around humans and regularly encounter objects that do not exist in the wild. He says similar experiments should eventually be conducted with less cultured apes, ideally wild populations.
Combining observations from both experiments, the team concluded that transparency and geometric shape appear to be the features that make crystals particularly attractive. The same properties may also explain why early humans chose to collect them.
Unlike trees, mountains, rivers, clouds and animals, which are dominated by curved and branching shapes, crystals stand out because of their flat surfaces and straight edges. They are the only naturally occurring polyhedral solids, making them unlike almost anything else in the natural landscape. Researchers suggest that these unusual patterns may have attracted the attention of early humans as they tried to understand the world around them.
Garcia-Ruiz concludes, “Our work helps explain our fascination with crystals and contributes to understanding the evolutionary roots of aesthetics and worldview.” “We now know that crystals have been present in our brains for at least six million years.”