Picture this: 15,000 years ago, somewhere near a river, two hairy, unwashed early humans—let’s call them Grug and Blorg—are deep in
negotiations over a freshly caught salmon. Grug, an expert spear-thrower, has just landed a hefty fish. Blorg, on the other hand, is a skilled toolmaker who knows Grug needs a new spear tip. The barter begins.