In a shallow cave on an island north of Australia, researchers have made a surprising discovery: the 42,000-year-old bones of tuna and sharks that were clearly brought there by human hands. The find, reported online today in Science, provides the strongest evidence yet that people were deep-sea fishing so long ago. And those maritime skills may have allowed the inhabitants of this region to colonize lands far and wide.

The earliest known boats, found in France and the Netherlands, are only 10,000 years old, but archaeologists know they don't tell the whole story. Wood and other common boat-building materials don't preserve well in the archaeological record. And the colonization of Australia and the nearby islands of Southeast Asia, which began at least 45,000 years ago, required sea crossings of at least 30 kilometers. Yet whether these early migrants put out to sea deliberately in boats or simply drifted with the tides in rafts meant for near-shore exploration has been a matter of fierce debate.

Indeed, direct evidence for early seafaring skills has been lacking. Although modern humans were exploiting near-shore resources, such as mussels and abalone, by 165,000 years ago, only a few controversial sites suggest that our early ancestors fished deep waters by 45,000 years ago. (The earliest sure sites are only about 12,000 years old.) Among the skeptics was Susan O'Connor, an archaeologist at the Australian National University in Canberra. "The evidence was pretty slim," she says....