/ 17 October 2007

Mussel power: How seafood encouraged migration

Archaeologists have uncovered the earliest known remains of human habitation at the coast, a finding that may explain how humans ventured beyond Africa at the start of their planetary odyssey.

Mussel shells, sharpened pieces of red ochre and stone micro-tools found in a sea cave in South Africa suggest that Homo sapiens headed for the beach quite soon after emerging from the savannah, they say.

By stumbling upon the rich harvest of the sea, man found the means to explore beyond Africa, sustaining himself through maritime edibles by probing along the coast, they suggest.

Until now, the earliest evidence of human settlement by the coast dates from 120 000 years ago — about 80 000 years after the approximate time when, according to fossil evidence, Homo sapiens arose in the grasslands of East Africa.

Experts have long suspected that coastal migration must have occurred earlier than this.

The problem, though, has been finding proof to back this belief.

Turn the clock back to an era between 195 000 and 135 000 years ago, and you will find Earth in the grip of an Ice Age.

So much water was locked up in glaciers that the sea level was as much as 125m lower than today. When the glaciers eventually retreated, the sea rose once more, swamping coastlines and sweeping away the traces of habitation.

One remarkable location that survived, though, was a cave overlooking the Indian Ocean in coastal cliffs at Pinnacle Point, near South Africa’s Mossel Bay.

The cave is so high that, even now, it is 15m above the sea. At the time when it was inhabited, it was located within 5km to 10km of the coast.

Curtis Marean of Arizona State University led a team that sifted through the cave’s walls and floor and found remains of hearths, of some two dozen shellfish, mainly brown mussels, as well as 57 pieces of ochre pigment, some of them brilliant red, and nearly three dozen ”bladelets,” or tiny tools made of chipped stone.

The find has been dated to around 164 000 years ago, give or take 12 000 years, according to their paper, which appears on Thursday in the British weekly journal Nature.

Marean believes the discovery opens a door to understanding the movements of our early forebears.

During the long glacial period, Southern Africa was cooler and drier, and hunter-gatherers probably found it hard to get food from animals, fruits and berries, he says.

Moving to the coast thus opened up a whole new larder of food.

”Shellfish may have been a critical food source to the survival of human populations when they were faced with depressed terrestrial productivity during glacial stages … when much of Southern Africa was more arid and populations were isolated and perhaps concentrated on now-submerged coastal platforms,” the study says.

Seafood was the biggest shift in the human diet until animal farming began at the end of the last Ice Age, roughly 11 000 years ago, it contends.

Once humans realised the bounty of food that lay within their grasp, they could use it for sustenance as they moved out of Africa, along the coast of the Red Sea and northwards into the Middle East and beyond, as the species embarked on its trek around the world.

Humans expanded into Southern Asia along the coast and also island-hopped their way to Australia and New Guinea using coastal food resources.

In a commentary, also published by Nature, anthropologist Sally McBrearty of the University of Connecticut and palaeontologist Chris Stringer of London’s Natural History Museum say the pigment is an equally exciting find.

This substance, also called haematite, has some practical use as an adhesive.

However, the brilliant red colours that feature in the find suggest it was also used for decorating the body or objects, given that red has always played a key role in human rite and society.

”It suggests that early humans in Africa inhabited a cognitive world enriched by symbols before 160 000 years ago,” the pair say. – Sapa-AFP