Ancient tools show how humans adapted to rainforests

The objects were found in a cave in Sri Lanka and include the oldest known bow-and-arrow technology outside Africa, dating back to 48,000 years ago.

Tuesday, June 16, 2020,
By Tim Vernimmen
Photograph by Image by M. C. Langley

At a jungle-covered cave site in southwestern Sri Lanka, archaeologists have found a remarkable collection of ancient objects, including tools that they believe are among the oldest survival gear humans used in rainforests.

The artifacts range in age from 48,000 to 4,000 years old and include 130 bone arrow tips—the oldest arrow tips found outside of Africa—as well as 29 bone tools for making bags or clothing and a handful of ornamental beads. Archaeologists discovered the objects as they excavated the cave and believe they correspond to four distinct phases of human habitation of the site, with arrowheads and awl-like tools first appearing in the earliest phase. Thirty items from the site have also been dated using radiocarbon technology, allowing researchers to create a timeline and see how the tools grew more sophisticated over the centuries.

“Most of these tools were made out of monkey bone, and many of them appear to have been carefully shaped into arrowheads,” says archeologist Michelle Langley of Griffith University in Australia, who lead the new research published in the journal Science Advances. “They are too small and light to have been spearheads, which need some weight to gain force, and too heavy and blunt to have been blow darts.”

Tools made from bone and teeth were used to hunt small monkeys and squirrels, work skins or plants, and perhaps create nets at Fa-Hien Lena, Sri Lanka. Here a possible net shuttle, monkey tooth awl/knife, and projectile point are shown.

Photograph by M. C. Langley

The arrow tips show evidence of having been attached to shafts, as well as small fractures that may have originated when they hit something. The bows they went with “would have been made from perishable plant materials,” Langley says, and haven’t survived the millennia. But the collection of bone tools that were preserved reveal some of humans’ earliest steps into the rainforest.

Adapting to a new home

While the main wave of humans is believed to have migrated out of Africa around 60,000 years ago, smaller groups appear to have started leaving between 200,000 and 100,000 years ago, and they expanded across significant portions of the planet. By 85,000 years ago, modern humans had arrived on the Arabian Peninsula. About 15,000 years later, they were in Southeast Asia, and by 65,000 years ago, they had made it all the way to Australia.

Along the way, Homo sapiens encountered and adapted to many challenging environments, from the freezing cold of the Siberian Arctic to the high altitudes of the Tibetan Plateau. When humans migrated into South Asia, they encountered yet another intimidating new habitat: the tropical rainforest, where dense vegetation, elusive prey, persistent insects, and well-camouflaged predators made it challenging for humans to survive.

As modern humans presumably made their way along the coasts of South Asia and into Sri Lanka about 48,000 years ago, they didn’t enter the dense forests right away. “The first people arriving on the island were probably living along the coast,” says archaeologist Oshan Wedage of the University of Sri Jayewardenepura in Sri Lanka, who has led a number of excavations in and around the Fa-Hien Lena cave. “But as the population grew, some of their descendants may have moved into the rainforest.”

The new environment would have required some important innovations. “In the plains, people were hunting big animals living in large groups that were easy to spot and target,” Langley says. “But in the tropical forest, many prey are very agile and may live high in trees. A spear isn’t particularly useful for catching a monkey or a squirrel in a forest, you need something that’s swift and that can go high. Bows and arrows are ideal for such an environment.” In turn, the monkey bones made excellent material for new arrow tips.

Some of the bone tools appear to have served other purposes. “One flattened piece of bone looks quite like a net shuttle, the kind of tool people use to drag the thread along when making or fixing a net,” Langley says, which would have been useful along the inland rivers as well as on the coasts. Other tools look like they were used to work leather and plant fibre, possibly into bags or even clothes. “People in the rainforest didn’t need many clothes to stay warm, but maybe they were useful to protect their skin from injury by insects or the vegetation,” Wedage says.

Archaeologist Ian Gilligan of the University of Sydney, who studies the early history of clothes, says he would not be surprised if humans were making clothing in Sri Lanka during this time. Genetic evidence from body lice, for example, which would have needed clothing to survive on humans, suggests that Homo sapiens in Africa may have been wearing clothes as long as 170,000 years ago.

“As the wearing of garments became more established, clothes acquired social functions, and no doubt these became a dominant factor in maintaining their use in many regions,” Gilligan says.

Cultural artifacts like clothes and beads may have helped humans weave tightly knit social groups, allowing them to be successful in almost every environment they encountered. New tools that nimble minds came up with could be shared with others, inherited and improved across generations.

Maintaining ties with old relative

Though people in the forest were forging a new way of life, they also appear to have maintained a connection with the populations they broke off from. Beads made out of the shells of marine animals, some of which were discovered in the rainforest cave about 25 miles from the shore, suggest that the Fa-Hien Lena group may have traded with other of people who stayed along the coasts, Wedage says.

The beads were rounded, polished, and pierced so they could be slung on a string. The oldest ones were made of shell, but later on, some were crafted from bright red ochre nodules.

“I am not sure whether people would have used the ochre beads as an ornament,” Langley says. “Maybe this was just a way to keep them together and carry them around, as they may have been used to decorate the body otherwise, by scraping them to release colourful powder that people could then spread on their skin.” Apart from three distinctive ochre beads, which are no older than 8,700 years, the researchers discovered 136 other fragments of yellow, red, and silver-colored mica, including from the oldest layers in the cave, that also may have been used to decorate the body by scraping off powder.

“Bright red often seems to be the first color people want to paint themselves with, usually in combination with white,” Langley says. “These colours have been found from Blombos Cave in South Africa all the way to Australia and beyond.” So it seems that even as groups of Homo sapiens spread around the world, steadily adapting their toolkit to the mountains or the Arctic or the rainforest, they kept some favourite colours wherever they went.

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