Reid Ferring holds a rock in each hand.

They are the size of hens’ eggs. They are oblong. They are grey. They are categorically ordinary. Aside from numbers inked onto their surfaces for cataloging purposes, they look like a quadrillion other natural stones scattered across the face of the Earth.

“The evidence is circumstantial,” Ferring, an American archaeologist, admits. “But we’ve got some good indications they were thrown.”

He is talking about prehistoric pitching.

Hundreds of such nondescript cobbles have been unearthed near the remains of prey animals at Dmanisi , an important hominin site in the forested hills of the former Soviet republic of Georgia.

Homo erectus, the first rambler out of Africa, scavenged through a Pleistocene boneyard here 1.8 million years ago. Our dawn ancestors appear to have chucked rocks at saber-toothed tigers, leopards, wolves, and hyenas to drive them from their kills.

Ferring’s drab cobbles could be the oldest weapons in the world.

“The Dmanisi people were small. They weren’t very powerful, they didn’t have fangs or claws,” says Ferring, a grandfatherly professor from the University of North Texas. “This place was filled with big cats. So how did hominins survive? How did they make it all the way from Africa? Rock throwing offers part of the answer.”

Over the past century, scientists have charted humankind’s evolution using a series of epic milestones: walking upright, tool making, harnessing fire.

But in recent years, experts such as Ferring are digging into an overlooked but equally transformative innovation: not what a stone tool accomplishes in the hand, but what it does after leaving it—at high velocity. Hurling rocks, these researchers say, helped make us fully human.

View Images Archaeologist Reid Ferring displays some possible projectiles. Photograph by Paul Salopek

How?

By socializing us. Throwing stones on hunts, whether to topple deer or rob meat from a lion, involved bombardments by small groups of people: an early collaborative activity.

In addition, the finesse required to whip a stone at a target is thought to be a neurological bridge to later breakthroughs, especially language . Broca’s area, the brain region responsible for intricate hand-eye coordination, is also associated with higher mental functions such as speech and communication.

“Ability to throw was probably achieved at an early stage in human evolution but has received little scholarly attention,” archaeologist Barbara Isaac declares in a pioneering 1987 article, “Throwing and Human Evolution,” wherein she blames “modern city dwellers and scholars” for missing the forgotten power of a well-aimed stone.

European colonists, she reminds us, were astonished by aboriginal Australians’ ability to fire deadly sprays of cobbles “with such rapidity that they seemed poured from some machine.” And an 18th-century account of South Africa’s nomadic San described a hunter nailing “a target the size of a coin with a stone from a hundred paces.” A Tanzanian man in Isaac’s own archaeological team once knocked down a zebra from a distance of 30 to 40 yards with a fist-size stone to the head.

These examples involve modern humans. The overhand throw is much older. It is pre-human.

Many primates—chimpanzees in particular—sometimes fling objects wildly at each other or at predators. (A loutish chimp in a Swedish zoo is famous for secretly caching rocks in the morning to zing at human visitors later in the day.)

Pinpointing that evolutionary transition—from a frightened ape blindly tossing a tree branch at a leopard to Nolan Ryan drilling a hundred-mile-an-hour fastball over home plate—is likely impossible. Unlike spears, which at their oldest date back 400,000 years , rock projectiles are millions of years old. They are neither purposefully chipped nor flaked. They do not announce themselves. They are mute.

View Images Students from across the globe participate in a summer dig at Dmanisi. Photograph by Paul Salopek

Some Clues

Van Gogh could have painted the Dmanisi site. Archaeology students from around the globe walk past farmers' haystacks and lush green pastures to search for stone tools and fossil bones. One of the dig pits is large enough to swallow a multi-story house. The volcanic soil has disgorged the oldest hominin fossils outside of Africa.

The people were petite for Homo erectus—slightly more than five feet tall. They weighed about a hundred pounds. They carried around a brain less than half the size of a modern human’s. Yet they seem to have competed well in a mosaic forest patrolled by unusually high densities of carnivores: giant leopards, lions, wolves, and hyenas. This was a million and a half years before the idea of a spear.

“They were cleverer than we think,” says David Lordkipanidze, the director of the National Museum of Georgia and the research coordinator of the site. “They came from Africa and adapted. They probably lived in groups and learned from other animals—other social hunters.”

And probably, they rocketed stones.

“Let a carnivore do all the work, then pelt it with rocks and steal its meal,” Ferring explains. “But do you know how hard it is to scare a lion away from its kill? You needed coordinated attacks.”

Proving somebody tossed a rock nearly two million summers ago is not easy.

Ferring bolsters his hypothesis with the odd assemblages of natural stones found near butchered kills at Dmanisi. He has discovered rock piles that suggest “ammo dumps” for keeping angry predators at bay. He has mapped carcasses that are peppered with rocks—the aftermath, perhaps, of human bombardments, to flush out a snarling feline. He is seeking telltale rings of rocks around kills: the Stone Age artillery of band of weak humans gorging on meat—turning, anxiously, to cast rocks at a predator circling 20 or 30 yards away.

The rocks are just rocks. Each one weighs between seven and ten ounces. A good heft. They fit comfortably in the palm.