Water’s Edge Ancestors

Human evolution’s tide may have turned on lake and sea shores

In a cave hugging South Africa’s lush southern coastline, Curtis Marean suspects he has cornered a wily Stone Age crew that brought humans back from extinction’s brink. These plucky refugees of continent-wide desolation were able to pull off such a stunning evolutionary turnaround because they got lucky. A coastal oasis near the bottom of the world spread its sheltering arms in the nick of time.

Stone age human ancestors residing near caves at South Africa’s Pinnacle Point (shown) may have learned to track the tides in order to harvest shellfish. Some propose that this type of activity may have played an important role in human evolution. SACP4

Seashells found at a South African cave were probably carried there by early peoples. A. Jerardino and C. Marean/Journal of Human Evolution 2010

SOUTHERN BOUNTY The distance between a Pinnacle Point cave labeled 13B and the shoreline changed over time. Shellfish collection probably occurred at times when the coast was within 10 kilometers (highlighted below), though the harvest probably changed with sea level. Africa map: geoatlas/graphi-ogre, adapted by Janel Kiley; receding shoreline map: A. Jerardino and C. Marean/Journal of Human Evolution 2010, adapted by Janel Kiley

Stone tools from Channel Island sites dating to 12,200 years ago suggest that the first colonizers to the New World may have come by sea. Univ. of Oregon

Marean proposes that it was there, where the Arizona State University archaeologist now conducts excavations, that humankind’s mental tide turned sometime between 164,000 and 120,000 years ago. Seaside survivors learned to read the moon’s phases in order to harvest heaps of shellfish — brain food extraordinaire — during a few precious days each month when ocean tides safely retreated.

Tantalizing traces of complex thinking and behavior, including lunar literacy, have turned up at South Africa’s Pinnacle Point, a cave-specked promontory that juts into the Indian Ocean. Chunks of dark red pigment and strikingly beautiful seashells found by Marean’s team in one cave attest to ancient ritual activities. Stone points unearthed in the same cave sport glossy patches, signs that the rock was heated to make it easier to work with. The finds challenge the long-standing view that Stone Age people did not think abstractly and perform complex rituals until about 50,000 years ago.

People chanced upon Pinnacle Point and its dietary bounty, Marean says, only after global cooling had rendered much of Africa barren and uninhabitable. Several genetic studies suggest that modern human numbers throughout Africa plummeted to a few hundred breeding individuals around that difficult time.

“Our excavations may have intercepted ancient people who shadowed the shifting shoreline and are the ancestors of everyone on the planet,” Marean says.

Research on Pinnacle Point’s mussel-seeking moon trackers exemplifies a growing scientific conviction that fish and shellfish have played a largely unappreciated role in brain and mind evolution throughout the history of the Homo genus, which appeared at least 2 million years ago and includes people today. Though several East African savanna sites contain butchered animal bones, signaling carnivorous tastes among human ancestors, some scientists now argue that red meat has been oversold as a dietary staple.

At a meeting of the American Association of Physical Anthropologists, held in Minneapolis in April, researchers argued that ancient menus focused heavily on food from lakes, rivers and oceans. New work presented at the meeting pointed to lakeside fishing in East Africa nearly 2 million years ago, the shoreline shellfish harvesting among Homo sapiens at Pinnacle Point starting more than 160,000 years ago and sea voyages to Pacific Ocean islands by an unlikely group of New World settlers around 12,000 years ago.

Food scientists at the meeting emphasized that nutrients essential for brain growth are much more abundant in fish and shellfish than in red meat or any other food. And grabbing catfish out of shallow waters, not to mention scooping up handfuls of shellfish along the shore, may be far easier than hunting land animals or scaring predators away from meaty carcasses, says archaeologist Jon Erlandson of the University of Oregon in Eugene.

Shellfish collecting and fishing probably began early among members of the Homo genus, Erlandson says. “These foods later could have provided nutrients that enabled the evolution of fully modern brain size and cognition.”

Olduvai gorging

Erlandson suspects that, before Homo sapiens’ Pinnacle Point pursuits, fishing was a catch-as-catch-can affair. Consider ancient cuisine unearthed on the eastern shore of Kenya’s Lake Turkana. Someone there bellied up to an aquatic buffet nearly 2 million years ago, leaving a mess that only an evolutionary scientist could love.

At a site unceremoniously dubbed FwJj20, a team led by anthropologist David Braun of the University of Cape Town in South Africa unearthed butchered remains of fish, turtles and crocodiles. Remains of animals that don’t live in the water but often reside nearby, such as tortoises, birds, giraffes, hippos, rhinos and antelope, also turned up. Stone tools lay among scraped and fractured shells of tortoises and water-dwelling turtles. Several catfish bones bore tool marks made by individuals who cut off the heads of their catches. Whatever members of the human evolutionary family once dined at FwJj20, they needed only basic implements to put catfish and other lake animals in hungry mouths.

“A large rock is probably all that ancient hominids would have needed to catch fish,” Braun said at the anthropology meeting. Even simpler fishing techniques may extend deep into primate prehistory. Orangutans have been found to snatch catfish from shallow ponds bare-handed and chase the finned snacks out of deeper water with poking sticks (SN: 5/7/11, p. 16).

A steady diet of fish would have nutritionally powered brain expansion in early members of the Homo genus, such as the untidy Lake Turkana crowd, in Braun’s view.

The Lake Turkana finds leave a sweet taste in archaeologist Kathlyn Stewart’s mouth. In a 1994 study, Stewart, of the Canadian Museum of Nature in Ottawa, concluded that abundant fish, crocodile and turtle remains at five sites within Tanzania’s Olduvai Gorge represented leftovers from hominid meals. Finds at these nearly 2-million-year-old locations, which have yielded fossils of early Homo and a related lineage called Paranthropus, also include butchered bones of land animals, which have received the lion’s share of scientific attention for more than 30 years.

Game hunting occasionally occurred at Olduvai Gorge, Stewart pointed out at the meeting in April, but aquatic foods provided stable, high-quality nutrition. Pollen data and chemical analyses of fossils indicate that hominids began hanging out in marshy areas, eating grasses and papyrus shoots, more than 3 million years ago, Stewart reported. Papyrus marshes feature a lot of fish, shrimp, snails, mollusks and microalgae, which the gorge residents also dined on. “Lake and river margins provided high-quality food to ancient hominids, especially pregnant and lactating females,” Stewart says.

Some researchers argue that a few aquatic munchfests don’t confirm that ancient hominids across East and South Africa fancied fish. Doubters and advocates alike await finds from more digs along African lakeshores and riverbanks.

Coast with the most

Marean suspects that such excavations will demonstrate that an increasing taste for catfish and other water creatures accompanied increases in brain size among early Homo species. Stone Age people exploited that evolutionary endowment at Pinnacle Point, putting their outsized brains together to solve the puzzle of the tides, Marean says.

Protein-rich shellfish, loaded with omega-3 fatty acids crucial for brain development, led to further social innovations, including a move from eating for now to organizing seaside harvests for later, in his opinion. If so, a sense of time needed to plan for the future characterized the human species almost from its start about 200,000 years ago.

Marean’s team previously reported that mounds of brown mussels and local sea snails excavated in one Pinnacle Point cave date to 164,000 years ago, providing the earliest evidence of coastal dwellers scarfing shelled food with relish, if not condiments (SN: 10/20/07, p. 243).

The researchers have since found that, by 110,000 years ago, limpets and sand mussels joined the menu. Shellfish foragers face their own brand of perils, Marean explains. Mussels, limpets and sea snails live in treacherous rocks that border the ocean. If the tide is not at its lowest, incoming swells can easily knock collectors onto sharp rocks or into the sea.

The cave excavated by Marean’s group sat two to five kilometers inland around 164,000 years ago, when sea levels were lower than today. Early foragers must have scheduled their activities around the best times to go to the coast for shellfish. When tides were high, foragers instead headed inland eight to 12 kilometers to exploit other foods in South Africa’s rich Cape Floral Region. This 90,000-square-kilometer strip curves around the bottom of Africa like a half-smile. Many plants in the Cape Floral Region produce edible geophytes, underground energy-storage organs that swell with carbohydrates at certain times of the year.

Coastal residents dug up geophytes and hunted inland game until the moon issued a call to the sea, Marean proposed at the anthropology meeting. When the sun and moon align, their combined gravitational forces cause daily tides to spring back and forth from extremely low to extremely high levels. Such spring tides, a twice-monthly effect that has nothing to do with the seasons, correspond to full and new moons.

During spring tides, low tides advance by 50 minutes each day. Fishers and other coastal devotees today consult printed tide schedules or programmed watches to coordinate activities with daily tidal rhythms. Pinnacle Point’s Stone Age crowd informally estimated each day’s prime time for shellfish collecting, Marean suggests.

Access to shellfish wasn’t always available during the Stone Age, though. Climate and environmental records indicate that South Africa’s coastline repeatedly advanced and retreated between 195,000 and 123,000 years ago. Thanks to a gently sloping continental shelf off much of the coast, as much as 95 kilo­meters of land was exposed when sea levels retreated during that period, Marean and his colleagues estimate.

Pinnacle Point attracted human visitors when its caves lay within about a day’s walk of the sea, the scientists assert. This off-and-on shoreline access over tens of thousands of years was enough to trigger big lifestyle changes. “Organizing foraging activities around a complicated system of tidal timing had a trickle-down impact on social life,” Marean says.

Abundant shellfish and geophytes made foragers less nomadic, increased birthrates and reduced infant death rates, Marean suggests. Burgeoning Pinnacle Point communities adopted symbolic and ritual behaviors, as well as advanced toolmaking techniques, to express social identities.

Tide tracking’s domino effect on mental and social life may have given modern humans a survival advantage when they met European Neandertals after leaving Africa. Caves overlooking the Mediterranean Sea in southwestern Europe contain remains of fish, seals and dolphins, as well as mollusks, eaten by Neandertals toward the end of their evolutionary run around 42,000 years ago (SN Online: 9/22/08). But these Neandertal caves contain no huge shell heaps that suggest that coastal visits occurred at tidal low points, when masses of mollusks lay exposed, Marean argues.

It seems that hungry Homo sapiens patiently consulted the moon, whereas Neandertals heeded the urgency of their grumbling bellies.

New World sea cruise
Tide tracking at Pinnacle Point led to expanding numbers of people who eventually turned to sea travel to find virgin territory. These seafood-lovers may well have colonized the world.
Starting around 50,000 years ago, ocean voyagers based in Asia fanned out across the Pacific to Australia and points beyond. These mariners have sailed under the radar of many scientists seeking the earliest settlers of the Americas, Oregon’s Erlandson asserted at the anthropology meeting.
Inland sites in North America contain stone points and mammoth bones that have nurtured a decades-old idea: The New World was first colonized by Asian big game hunters who crossed a land bridge to Alaska around 13,000 years ago. A corridor through massive ice sheets ushered these intrepid carnivores into what’s now the United States, where they founded the Clovis culture, named after a New Mexico site that has yielded stone spear points.
It’s now an open question whether the Clovis-first hypothesis will hold up, Erlandson says. In the March 4 Science, he and his colleagues reported that people lived on California’s Channel Islands by about 12,200 years ago. A sea cruise of nine to 10 kilometers was required to reach these ocean outposts.
Three Channel Island sites — seasonal camps, most likely — yielded narrow-stemmed stone points and crescent-shaped implements, lying among bones of seabirds such as geese and cormorants, seals and other sea mammals, and several types of fish. Piles of shells from red abalone, giant chiton, mussels and other shellfish also turned up.
Stone tools found on the Channel Islands look nothing like Clovis points. In an upcoming Quaternary International, Erlandson and Todd Braje of Humboldt State University in Arcata, Calif., argue that stemmed stone points found on the islands instead resemble those that have been found at coastal sites stretching from Korea, Japan and northeastern Russia to North and South America.
These finds date to between 35,000 and 15,000 years ago in Asia, and to as early as 14,500 years ago in the Pacific Northwest, Erlandson said at the meeting, supporting his suspicion that initial New World colonists used canoes or other vessels to navigate along the coast from Asia to the Americas. Stemmed points found around lakes and marshes in western North America look like Channel Island finds, indicating that coastal people not only cruised the open sea but headed inland, possibly to trade for goods with Clovis people, Erlandson says.
“We have to start creating new models of the peopling of the Americas,” he says. “Received wisdom and a good story can inhibit research for decades, as happened with the Clovis hypothesis.”

Inundated evidence
Encroaching oceans also inhibit investigations of humankind’s water-traveling ancestors. A global sea level rise of about 120 meters between 20,000 and 6,000 years ago flooded shorelines and nearby lowlands where ancient populations presumably camped. “Current evidence for Stone Age coastal occupations represents the tip of the iceberg,” Erlandson says.
Yet the patchy evidence available for ancient tide tracking on South Africa’s coast leaves some researchers skeptical. A connection between shellfish harvesting at Pinnacle Point and a rapid transformation in human thinking remains questionable, argues Stanford University archaeologist Richard Klein.
Coastal caves bearing stone tools and seafood remains from more than 164,000 years ago may yet be found, he asserts. And shellfish gathering requires no special knowledge, tools or personal risk if the tide happens to be out. Coastal baboons in Africa collect and eat shellfish. Seagulls drop mussels and other tidal treats on hard ground to break open shells, leaving behind what sometimes looks like human garbage, Klein says. Also, abundant archaeological evidence of fish eating by Europeans and Africans dates to no more than 50,000 years ago, long after brain size had ballooned.
“It will take a long time to test my hypothesis about an ancient coastal adaptation in South Africa,” Marean acknowledges. Prime shoreline camps from long ago undoubtedly lie under­water, “guarded by great white sharks and dangerous currents,” he says.
He and his colleagues are now exploring more caves at Pinnacle Point and have expanded their search to caves on South Africa’s eastern coast. Some of these sites are located where the continental shelf drops steeply and the coast was always near, possibly giving researchers access to ancient camps that never got inundated by the ocean.
Marean looks forward to further encounters with long-dead lunar tide trackers. This is, after all, no fishing expedition.

Bruce Bower

Bruce Bower has written about the behavioral sciences for Science News since 1984. He writes about psychology, anthropology, archaeology and mental health issues.

More Stories from Science News on Humans

From the Nature Index

Paid Content