By Paul Rincon
Science reporter, BBC News
Learning how to live off the sea may have played a key role in the expansion of early humans around the globe.
Coastlines were rich in resources for early humans
After leaving Africa, human groups probably followed coastal routes to the Americas and South-East Asia.
Professor Jon Erlandson says the maritime capabilities of ancient humans have been greatly underestimated.
He has found evidence that early peoples in California pursued a sophisticated seafaring lifestyle 10,000 years ago.
Anthropologists have long regarded the exploitation of marine resources as a recent development in human history, and as peripheral to the development of civilisation.
This view has been reinforced by a relative lack of evidence of ancient occupation in coastal areas.
But that view is gradually changing; genetic studies, for example, suggest a major early human expansion out of Africa occurred along the southern coastline of Asia, leading to the colonisation of Australia 50,000 years ago.
The knotted "cordage" could have been used to make nets and lines
Shifting sea levels since the last Ice Age, combined with coastal erosion, would have erased many traces of a maritime past, Professor Erlandson explained.
"The story of human evolution and human migrations has been dominated by terrestrial perspectives," the University of Oregon researcher told BBC News.
"I grew up on the coast and I always thought this didn't make much sense. Coastlines are exceptionally rich in resources."
Professor Erlandson has carried out extensive excavations on San Miguel Island, off the coast of California, which is known to have been inhabited at least 13,000 years ago.
About 100,000 seals and sea lions of six different species live on the island. These slow-moving sea mammals would have been easy prey for the island's early human inhabitants.
Seals would have been easy prey for hunters
"The big elephant seals weigh over 3,000lbs," he explained. "It has always seemed to me that these were a resource that early humans would not want to miss."
One of the digs, at Daisy Cave, on San Miguel Island, has yielded about 20 bone "gorges", a form of fish hook.
The gorges were covered with bait to be swallowed whole by fish, which were then reeled in. These are between 8,600 and 9,600 years old and are associated with more than 30,000 fish bones. They are the oldest examples of such artefacts in the New World.
The researchers have also recovered fragments of knotted "cordage" - woven seagrass - that might have been used to make fishing nets. These delicate items were preserved by pickling under layers of ancient cormorant dung.
"The preservation is superb, so we interpreted the cordage as 'cut-offs' from the manufacture and maintenance of nets, fishing lines, and other maritime-related woven technologies," Professor Erlandson said.
At other sites, the researchers have found barbed points that were most likely used for hunting sea mammals - possibly sea otters. They also unearthed examples of 9,000-year-old basketry as well as 8,600-year-old shell bead jewellery.
The findings from Daisy Cave could be consistent with the idea that some of America's first colonists followed a coastal migration route from Asia.
Conquering the cold waters of the northern Pacific would have required advanced seafaring skills as well as an ability to successfully exploit marine resources.
The gorges are a form of fishing hook
At the height of the last Ice Age, a land mass called Beringia would have connected North-East Asia to North America.
Traditionally, the first Americans were thought to be big game hunters, who marched from Siberia across the land bridge to Alaska. Then, they were thought to have travelled south through the Canadian Arctic via an "ice-free corridor" that emerged in the central US.
But the earliest signs of human occupation from the ice-free corridor date to 11,000 years ago, while California's Channel Islands are now known to have been inhabited at least 13,000 years ago.
Professor Erlandson has come up with an alternative theory that maritime peoples from Asia followed forests of kelp to the New World.
Kelp Forest would have hugged the coastline from Japan up through Siberia to Alaska and down along the Pacific coast of North America. This marine plant grows in rocky, nearshore habitats and cold water up to 20C.
Humans may have followed the kelp from Siberia to America
It creates rich ecosystems, providing habitats for seals, sea otters, hundreds of fish species and shellfish. These could have been important sources of food and other resources such as skins for early peoples.
However, the professor of archaeology says "actually proving such a migration took place is a very difficult thing to do because of sea level changes and coastal erosion".
He added: "I think the peopling of the New World was much more complex than has traditionally been viewed. I think it probably involved maritime and terrestrial migrations."
Jon Erlandson was speaking at the Calpe Conference 2006 in Gibraltar.