Deep in a sulfur cave in southern Mexico, a group of indigenous people have for centuries asked their gods for bountiful rain by stunning the cave's fish with a natural plant toxin. Once the fish have succumbed, the Zoque people scoop them into baskets for eating. Now scientists are finding the ancient religious practice is impacting the fish's evolution.
Those fish that are resistant to the anesthesia survive to pass on their genes, while the others simply meet their demise.
The religious ceremony is held in the sulfur cave Cueva del Azufre each year at the end of the dry season during the holy week before Easter. The Zoque grind up the toxic, carrot-shaped roots of the tropical barbasco plant and mix them with lime to form a paste, which they wrap in leaves. They place the bundles about 110 yards (100 meters) into the cave to poison its waters and anesthetize fish, which the Zoque believe are gifts from gods that inhabit the underworld. The collected fish supplement the meals of the Zoque until crops are ready for harvest.
