Discover 1-2

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12 DISCOVERMAGAZINE.COM

FROM TOP: KATE JOHNSON/SAN DIEGO NATURAL HISTORY MUSEUM; TOM DÉMÉRE/SDNHM; SDNHM

Stateside Stones and Bones

A Nature study published in April made a startling claim: Rounded

stones found beside fractured mastodon bones near San Diego

were evidence of someone processing the animal’s remains 130,

years ago.

The current timeline for humans arriving in the Americas,

however, is a mere 15,000 to 20,000 years ago, via Siberia and the

now-submerged land bridge Beringia. Many in the field are highly

skeptical of the Nature paper.

“These are just naturally occurring rocks that, over time, have

broken along existing fractures,” says Texas A&M University

archaeologist Michael Waters. “The evidence for early human

occupation is not there.”

Found during highway

construction in 1992, the

Southern California site yielded

the stones and mastodon bones,

several of which were fractured

or in unusual positions. But the

items weren’t interpreted as

evidence of hominin activity until

recently, when they drew the

interest of Steven Holen, lead

author of the Nature paper.

“My first reaction was, ‘This

is not possible,’ ” Holen says. His

team took a multidisciplinary

approach to analyzing the

material, from sophisticated

dating techniques to re-creating

the kinds of fractures such stones

might have made, using fresh

elephant bones in Africa.

Holen argues fluctuating

sea levels exposed Beringia

130,000 to 160,000 years ago,

when bison crossed the land

bridge into the Americas. It’s

possible, he believes, that a

population of hominins — Neanderthals, Denisovans or even

archaic Homo sapiens — followed the animals.

Holen says he knew his paper would ignite controversy, and that

he’d be the first to admit “you need to have more than one site if

you’re going to have a paradigm shift.” He hopes more researchers

will remain open-minded.

“The most important thing for a reader to take away from this,

and also for young scientists in general, is that we don’t have all

the answers,” Holen says. “That’s why we do science."

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A museum drawer full of fossils from a Southern

California site. The remains hint at the fact humans

might have arrived in the Americas more than 100,

years earlier than we thought.

Researchers argue that around

130,000 years ago, hominins used

the stones above like a blacksmith

uses an anvil. But instead of

hammering metal, these archaic

tool-wielders processed animal

remains.