Chimpanzees’ Fascination with Crystals Offers Clues to Human Ancestors’ Behavior

For hundreds of thousands of years, crystals have been found at archaeological sites alongside Homo remains. Evidence suggests hominins—the ancestors of modern humans—have been collecting these stones for at least 780,000 years ¹. A long-standing mystery has been why these crystals were collected, as they weren’t used as tools, weapons, or jewelry. New research suggests that this fascination may be rooted in our evolutionary history, with chimpanzees exhibiting a similar attraction to crystals.

Why Did Hominins Collect Crystals?

Scientists have long puzzled over the purpose of crystal collections found at archaeological sites. The fact that these objects served no obvious practical function led researchers to investigate the underlying reasons for this behavior. A recent study published in Frontiers in Psychology explored this question by examining the behavior of chimpanzees, our closest living relatives ².

Experiments with Chimpanzees

Researchers in Spain conducted experiments with chimpanzees from the Rainfer Foundation, who were accustomed to interacting with humans ³. The experiments aimed to identify the physical properties of crystals that might attract both chimpanzees and their hominin ancestors.

The “Monolith” Experiment

In the first experiment, a large quartz crystal – referred to as the “monolith” – was placed alongside a normal rock of similar size. Initially, both objects garnered the chimpanzees’ attention, but the crystal quickly became the focus. Once the chimpanzees retrieved the crystal, they carefully examined it, rotating and tilting it to view it from different angles. One chimpanzee, Yvan, even carried the crystal to his sleeping area ³.

The chimpanzees’ interest in the crystal was strongest initially, then gradually declined over time, mirroring a pattern often observed in humans when their curiosity about a new object wanes. Notably, when researchers attempted to retrieve the crystals, they had to trade them for the chimpanzees’ favorite treats – bananas and yogurt – demonstrating the value the chimpanzees placed on the crystals ³.

Identifying Crystals Among Pebbles

A second, more challenging experiment involved mixing small quartz crystals among a pile of 20 round pebbles. The chimpanzees were able to quickly and accurately identify and select the crystals from the pebbles, even when other types of crystals, such as pyrite and calcite (which have different shapes than quartz), were added ³.

The chimpanzees displayed a keen interest in the transparency of the crystals, holding them up to their eyes and looking through them. They repeatedly observed the crystals for hours, and one chimpanzee, Sandy, even carried pebbles and crystals in his mouth to a wooden platform, where he meticulously separated them ³.

Implications for Understanding Human Ancestors

“We show that enculturated chimpanzees can distinguish crystals from other stones,” said Prof. Juan Manuel García-Ruiz, lead author of the study and a professor of crystallography at the Donostia International Physics Center in San Sebastián ⁴. “We were pleasantly surprised by how strong and seemingly natural the chimpanzees’ attraction to crystals was. This suggests that sensitivity to such objects may have deep evolutionary roots.”

Given that modern humans and chimpanzees shared a common ancestor between six and seven million years ago, the shared fascination with crystals suggests that this attraction may be an ancient, inherited trait ¹.