Some 279,000 years ago, on a ridge overlooking a vast lake in central Ethiopia's Rift Valley, hunters painstakingly shaped chunks of greenish black volcanic glass into small, sharp points. After chipping the brittle material to create cutting edges, they attached each point to a shaft of wood, producing a sort of javelin. It might sound like a modest feat of engineering by today's standards. But the technology was nothing less than revolutionary. With it, members of the human lineage had at their disposal a weapon that would allow them to kill much more effectively from afar than a simple wooden spear could. Not only would that development enable our predecessors to hunt a broader range of animals, but it also upped their odds of emerging from the hunt unscathed by putting a safe distance between them and large, dangerous prey, perhaps including the hippos that would have lurked in and around the nearby lake.