A growing market for ejiao—a gelatin made from donkey hide believed by practitioners of traditional Chinese medicine to increase libido and slow aging—has led to a global trade of millions of donkey skins each year. Asses are often kidnapped from rural African villages, where their labor is valued highly, then taken to markets and slaughtered for export. “The donkeys,” said a sanctuary manager while visiting a market in Tanzania, “are very stressed.”

The head female of a paper-wasp nest allows others to occupy space in her home—so long as they help raise her offspring. The labor market is, however, elastic: if other nests nearby have childcare needs, she maintains a lower work requirement from her “helper” wasps.

Ottoman humorist Yusuf al-Shirbini of Egypt railed against unfair levies, referring to them as “things being called innovation.” Al-Shirbini quoted scripture: one who brings about “an innovation or provides accommodation for an innovator, upon him be the curse of God.”

When Arctic traveler Vilhjalmur Stefansson traded with the Inuit of Victoria Island in 1911, he found the metal of their knives to be of curious provenance: Inuit to the east had bought guns from the Hudson Bay Company and traded them westward; the firearms were then traded farther west, eventually reaching the Inuit he’d met—who, having no use for guns, had beat the metal barrels into knife blades.

A hand’s primary function, Elias Canetti writes in Crowds and Power, is as “a claw to grasp whole branches” while climbing; both hands partner in “grasping” and “letting go.” This is like trade, he argues: “one hand tenaciously holds on to the object with which it seeks to tempt the stranger” while the other “is stretched out in demand.” Trading, then, offers “profound and universal pleasure” as “a translation into nonphysical terms of one of the oldest movement patterns.”