Which Chimp Should Wield The Crystal?

More than a century ago, the Chinese paleontologist and archaeologist Pei Wenzhong found an unusual trove in the same cave near Beijing where he found the skulls of the early hominin Peking Man. Along with the remains of a 700,000-year-old Homo erectus , Wenzhong unearthed a collection of 20 quartz crystals, one of which was a "perfectly faceted, smoky quartz crystal," the researcher Juan Manuel García-Ruiz wrote in a 2018 paper. In 1931, Wenzhong brought the quartz back to Beijing. "After washing and displaying them, I invited my colleagues to observe them," Wenzhong wrote in an article. "One colleague seemed very angry after examining them, picked up a piece straight away, hit it hard on the other stone fragments, and exclaimed, 'These kinds of broken stones can be seen everywhere on the road!'" But later that fall, the French archaeologist Henri Breuil examined the crystals and agreed with Wenzhong: The crystals were not just stones, but artifacts collected by the early humans who lived in the cave.

Since Wenzhong's discovery, archaeologists elsewhere in Asia, Africa, and Europe have excavated quartz crystals from sites occupied by early humans. It's clear that Homo erectus and Homo sapiens collected crystals that were too small to be tools. Rather, these early hominins were attracted to the stones for some other reason. García-Ruiz, who studies crystallography at the Donostia International Physics Center in San Sebastián, Spain, has hypothesized that crystals were an early catalyst of abstract thinking, symbolism, and consciousness in hominins. Such a hypothesis would seem impossible to empirically test, given the extinction of Homo erectus and other early humans. So García-Ruiz turned to our closest living relatives, chimpanzees, to see if they, too, experience what he's dubbed the "crystal allure."

In a paper published today in Frontiers in Psychology , García-Ruiz and colleagues prove without a doubt that chimpanzees are drawn to crystals. The researchers offered crystals to nine chimpanzees living in two groups at a rehabilitation center in Spain. (The chimps, many of whom came from circuses, are all familiar with humans.) In one experiment, the researchers placed a clear quartz crystal and a voluptuous slab of sandstone, each larger than a human hand, on two pedestals. Via a feed from a video camera, the researchers observed the chimps approaching the pedestals, noting when the chimps interacted with either the crystal or the rock. In another experiment, the researchers offered the chimpanzees a scattering of stones and crystals in the grass to see which ones they picked up and examined.