Early humans were beachcombers who lived by the warm seas of East Africa and ate oysters, mussels and crabs.
An archaeological find, on the Eritrean coast, has produced the earliest evidence to show that man may have first colonised the world by migrating along beaches.
Exploiting the resources of the African coastline could have led to boatbuilding, navigation and eventually the discovery of South-east Asia and Australia, long before the first anatomically modern humans inhabited Europe.
It could also explain our modern-day predilection for seaside holidays.
A team of scientists led by Robert Walter, of the Centro de Investigacion Cientifica de Educacion Superior in Ensenada in Mexico, has found a set of stone tools 125,000 years old on the Red Sea coast site, which was rich in edible shellfish. "This is the earliest well-dated evidence for human adaptation to a coastal marine environment, heralding an expansion in the range and complexity of human behaviour from one end of Africa to the other," the scientists say in the journal Nature.
The tools include hand axes - teardrop-shaped pieces of sharpened stone - and deliberately flaked pieces of volcanic glass with razor-sharp edges that are capable of cutting through flesh.
Although the archaeologists cannot at present definitely identify Homo sapiens as the maker of the tools, they believe the artefacts were made by members of our own species. They match other stone tools of the same date found at other sites in Africa where anatomically modern humans were known to have lived.
In addition to the tools, the archaeologists found the remains of several edible marine animals, including oysters, mussels and crabs.
"The simplest explanation for the occurrence of stone tools [at the site] is that whoever made the tools used them to harvest edible - energetically profitable and palatable - shallow marine molluscs and crustaceans and to butcher large land mammals near the shore," the scientists say.
Professor Chris Stringer, the head of human origins at the Natural History Museum in London, said the find supports a new theory of how the first humans migrated out of Africa by following the eastern coastline, which would have led to Australia being discovered before Europe. He said: "The earliest evidence of modern humans in Europe is 40,000 years old whereas we find evidence dating to 60,000 years ago in Australia. The big question is 'how did they do it?' This provides a possible explanation."
Being well adapted to living off coastal animals, seabirds and shellfish, early humans would have preferred to move along the coasts rather than migrate to the less hospitable inland habitats of deserts and rainforests, Professor Stringer said, adding: "As the population grew and resources were depleted they would have moved further and further along the coast. Moving at a rate of one mile a year, it would only take 10,000 years to get from Africa to Australia."
Land bridges would have enabled the early migrants to get as far as Java without using boats but they must have built some sort of sea-going vessels to travel to Australia, Professor Stringer said.
The artefacts found on the coast of Eritrea are of the right age to suggest that early humans used the coastline to migrate to the Asian mainland, say Robert Walter and his colleagues. "It is now clear that the Red Sea basin, and perhaps the entire eastern shoreline of Africa, must be examined for additional evidence to test this model of early human occupation of coastal marine environments before 100,000 years ago, and its role in the dispersal of early humans out of Africa."
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