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October 18, 2007

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Trip to beach a milestone in human evolution: study

Oct. 17, 2007
World Science staff

One of the first things mod­ern hu­mans did when they evolved was head for the beach—a set­ting that may have served as a cru­ci­ble and driv­er of our ev­o­lu­tion, a new study sug­gests.

Its au­thors say they’ve found ev­i­dence of the ear­li­est known peo­ple with cul­tur­al trap­pings of the “mod­ern” hu­man spe­cies, such as use of sym­bols and in­no­va­tive tools, about 164,000 years ago. 

The red ar­row marks the en­trance to a cave where, re­search­ers say, they found what some of the first be­hav­ior­al­ly mod­ern hu­mans left be­hind. The shore­line may have moved since their time, but it was prob­a­bly with­in a few miles (km) of here—a rea­son­a­ble for­ag­ing dis­tance, ac­cord­ing to an­thro­pol­o­gists. (Cour­te­sy Cur­tis Marean)

­sands of years.

O­chre with scrape marks, thought to have been made by ear­ly hu­mans who used the red pig­ment in sym­bol­ic be­hav­ior such as body col­or­ing or art cre­a­tion. (Cour­te­sy Mos­sel Bay Ar­chae­ol­o­gy Proj­ect)

The work al­so could shed light on our spe­cies’ migra­t­ion out of its Af­ri­can birth­place, as some theo­ries hold that this jour­ney fol­lowed coast­lines, sci­en­tists said. “Coast­lines gen­er­ally make great migra­t­ion routes,” Mar­e­an re­marked. “Know­ing how to ex­ploit the sea for food meant these early hu­mans could now use coast­lines as pro­duc­tive home ranges and move long dis­tances.” 

The newly iden­ti­fied, an­cient coast dwellers used a bright red col­or­ing and “ex­panded their di­et to in­clude shell­fish and oth­er ma­rine re­sources, per­haps as a re­sponse to harsh en­vi­ron­men­tal con­di­tions,” added Mar­e­an.

Most schol­ars agree based on ge­net­ic and fos­sil ev­i­dence that mod­ern hu­mans, Ho­mo sapi­ens, evolved in Af­ri­ca be­tween 100,000 and 200,000 years ago. But ar­chae­o­log­i­cal sites from that time are rare in the con­ti­nent; and giv­en its huge size, it’s un­clear just where the step to mod­ern­ity oc­curred.

“The world was in a gla­cial stage” for most of this time, and much of Af­ri­ca was dry or des­ert, Mar­e­an said. “There are only five or six places in all of Af­ri­ca where hu­mans could have sur­vived.” Mar­e­an said he looked for a “per­fect site” to ex­plore by stu­dying ocean cur­rents, cli­ma­te da­ta, geolog­i­cal forma­t­ions and oth­er da­ta. He set­tled on the Cape of South Af­ri­ca at Pin­na­cle Point as a spot for in­vest­i­ga­tion.

The re­sults ful­filled all his hopes, he said.

One find­ing was “bladelets,” less than a cen­ti­me­ter wide, that “could be at­tached to the end of a stick to form a point for a spear, or lined up like barbs on a dart,” Mar­e­an said. This shows peo­ple “were al­ready us­ing com­plex com­pound tools. And, we found ev­i­dence that they were us­ing pig­ments, es­pe­cially red ochre, in ways that we be­lieve were sym­bol­ic.” The team re­ported find­ing 57 pieces of this ma­ter­ial, many ap­par­ently ground for use as a col­or­ing agent.

Ar­chae­o­lo­gists view sym­bol­ic be­hav­ior as a clue that lan­guage in the mod­ern sense may have been pre­s­ent, he added.

Dat­ing the find­s—which al­so in­cluded shell­fish re­main­s—was a chal­lenge, Mar­e­an said. This time pe­ri­od is be­yond the range of the most com­mon dat­ing tech­nique, car­bon dat­ing. But two oth­er cutting-edge meth­ods served to fill the gap, he added. One, known as lu­mi­nes­cence dat­ing, in­volved gaug­ing when in­di­vid­ual sand grains were last ex­posed to light; thou­sands of grains were meas­ured.

The dis­cov­er­ies change our pic­ture of early mod­ern hu­man ev­o­lu­tion in sev­eral ways, Mar­e­an added. “Gen­erally speak­ing, coast­al ar­eas were of no use to early hu­mans—unless they knew how to use the sea as a food source,” he said. “For mil­lions of years, our ear­li­est hunter-gatherer rel­a­tives only ate ter­res­tri­al plants and an­i­mals. Shell­fish was one of the last ad­di­tions to the hu­man di­et be­fore domestica­ted plants and an­i­mals were in­tro­duced.” The pre­vi­ously ear­li­est ev­i­dence for hu­man use of ma­rine re­sources and coast­al habi­tats dates to about 125,000 years ago, he said.

In a com­men­tary published with the stu­dy, two sci­en­tists not in­volved with it wrote that it pro­vides “strong ev­i­dence” for its claim of early mod­ern hu­man be­hav­ior at Pin­na­cle Point, whose ar­ea is now dotted with golf re­sorts. “The site pro­vides a rare glimpse in­to hu­man adapta­t­ion to coast­al con­di­tions,” added the writ­ers, Sa­lly Mc­Brear­ty of the Un­ivers­ity of Con­nect­i­cut and Chris String­er of Lon­don’s Nat­u­ral His­to­ry Mu­se­um.

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One of the first things modern humans did when they evolved was head for the beach—and this sandy zone may have served as a crucible and driver of our evolution, a new study suggests. Its authors say they’ve found evidence of the earliest known people with cultural trappings of the “modern” human species, such as use of symbols and innovative tools, about 164,000 years ago. Unlike their more primitive ancestors, this group lived near and harvested the sea—probably pushed by a dry, frigid climate to try this as a new survival gambit, according to the scientists. “We believe that on the far southern shore of Africa there was a small population of modern humans who struggled through this glacial period using shellfish and advanced technologies, and symbolism was important to their social relations,” said paleoanthropologist Curtis Marean of Arizona State University in Tempe, Ariz., one of the researchers. The people, who dwelt in a large, high cave overlooking the Indian Ocean, might have been “the progenitor population for all modern humans,” added Marean. His group reports its findings in the Oct. 18 issue of the research journal Nature. Exactly when the arguably “modern” human species emerged, is debated. Research has also pointed to a long delay between the origin of “modern” anatomy and, later, of “modern” behavior. A 2005 study, for instance, found that modern anatomy arose by 195,000 years ago. Not until about 100,000 years later do signs of modern behavior appear, in the form of beads thought to attest to the use of symbols, according to findings published last year. Thus, the new study doesn’t present the oldest evidence ever put forth for “modern” anatomy; but it does claim the earliest evidence of “modern” behavior, by far. The work also could shed light on people’s migration out of the species’ African birthplace, as this journey is also thought to followed coastlines, scientists said. “Coastlines generally make great migration routes,” Marean remarked. “Knowing how to exploit the sea for food meant these early humans could now use coastlines as productive home ranges and move long distances.” The newly identified ancient coast dwellers used a bright red coloring and “expanded their diet to include shellfish and other marine resources, perhaps as a response to harsh environmental conditions,” added Marean. Most scholars agree based on genetic and fossil evidence that modern humans, or Homo sapiens, evolved in Africa between 100,000 and 200,000 years ago. But archaeological sites from that time are rare in the continent; and given its huge size, it’s unclear just where the step to modernity occurred. “The world was in a glacial stage” for most of this time, and much of Africa was dry or desert, Marean said. “There are only five or six places in all of Africa where humans could have survived.” Marean said he looked for a “perfect site” to explore by studying ocean currents, climate data, geological formations and other data. He settled on the Cape of South Africa at Pinnacle Point as an ideal searching spot. The results fulfilled all his hopes, he said. One finding was “bladelets,” less than a centimeter wide, that “could be attached to the end of a stick to form a point for a spear, or lined up like barbs on a dart,” Marean said. This “shows [people] were already using complex compound tools. And, we found evidence that they were using pigments, especially red ochre, in ways that we believe were symbolic.” The team reported finding 57 pieces of it, many apparently ground for use as a coloring agent. Archaeologists view symbolic behavior as a clue that language in the modern sense may have been present, he added. Dating the finds—which also included shellfish remains—was a challenge, Marean said. This time period is beyond the range of the most common dating technique, carbon dating. But two other cutting-edge methods served to fill the gap, he added. One, known as luminescence dating, involved figuring out the last time individual sand grains were exposed to light; thousands of grains were measured. The discoveries change our picture of early modern human evolution in several ways, Marean added. “Generally speaking, coastal areas were of no use to early humans—unless they knew how to use the sea as a food source,” he said. “For millions of years, our earliest hunter-gatherer relatives only ate terrestrial plants and animals. Shellfish was one of the last additions to the human diet before domesticated plants and animals were introduced.” The previously earliest evidence for human use of marine resources and coastal habitats was dated about 125,000 years ago, he continued, so “our research shows that humans started doing this at least 40,000 years earlier.” In a commentary accompanying the study, two scientists not involved with it wrote that it provides “strong evidence” for its claim of early modern human behavior at Pinnacle Point, an area now home to an oceanside golf resort. “The site provides a rare glimpse into human adaptation to coastal conditions,” added the writers, Sally McBrearty of the University of Connecticut and Chris Stringer of London’s Natural History Museum.