Jungle
Page 13
“HURRY UP, PAT, it is about to rain!” yelled my former PhD student, Dr. Oshan Wedage of the University of Jayewardenepura, as I staggered behind him through the dense, lowland, evergreen rainforest of southwestern Sri Lanka. Drenched in sweat and covered in especially cunning leeches, which drop from the treetops as they feel your vibrations, I tried to pick up my pace. Not fast enough. The heavens opened, and we were now trudging uphill through the mud, undergrowth, and fast-running streams. The rest of the animal life was too smart to be out in this weather, giving this challenging habitat an even more “barren” appearance. At that moment it was very easy to see how many leading archeologists and anthropologists, and indeed the general public, might still think that the first human populations moving out of Africa would have actively avoided tropical forests. In fact, until the beginning of the twenty-first century, the earliest evidence for definite human occupation of a tropical rainforest environment was widely considered to be limited to the very final Pleistocene (18,000 to 11,700 years ago) or early Holocene (11,700 to 8,200 years ago), when further technological innovations may have made dealing with these challenging conditions and food sources more palatable. But then, from up ahead, Oshan shouted, “We’re here!” Out of the mist and water came a view of one of a cluster of cave and rock shelter sites in this part of the world that has been drastically challenging this antitropical forest bias.9
Sri Lanka is an island at the southern tip of South Asia, just below the Indian subcontinent and just above the equator. Sitting in the middle of the Indian Ocean, it is at a key location in models that assume a rapid “southern route” for humans from Africa all the way to Australia in the late Pleistocene. This expressway has been variously thought of as being driven by rich coastal resources, meaning that humans did not have to come inland to face more challenging environments, or by the periodic expansion of more familiar grasslands. But since Sri Lankan archeologists, like Oshan and his earlier mentor, Dr. Siran Deraniyagala, transformed Pleistocene archeology on the island, it has posed something of a problem for these blanket models. The site we came across at the end of our trek was Batadomba-lena, one of three caves, alongside the nearby Fa-Hien Lena and Kitulgala Beli-lena, that remarkably preserve the oldest human fossils anywhere in South Asia and some of the oldest material culture that can be confidently linked with our species in the region, dating to 45,000 years ago. As Oshan says, “Although people have often ignored our ‘Resplendent Isle,’ it plays a major role in perceptions of adaptations of Homo sapiens as it moved beyond Africa.” Instead of on the coast or in the drier, grassland areas of Sri Lanka, the island’s earliest, clear human sites are found in inland, wet tropical rainforests.10
Sure, you might be thinking, but these rainforests might not have been there in the past. It is also just an island, so maybe humans moved around a lot, only briefly visiting the forests. It was to address these considerations that I first traveled to Sri Lanka while working on my PhD. I instantly fell in love with the country and its people and have rarely spent more than a year away ever since. Back in 2015, working closely with archeologists like Oshan, we applied, for the first time, the stable isotope method I introduced in Chapter 5 to the rich record of human fossil teeth that had emerged from Sri Lanka’s rainforest caves and rockshelters. Comparing our results to those from animal teeth found alongside the humans, we were able to show that, unlike the African hominins, from 36,000 to 3,000 years ago, almost all of the individuals living at these sites had isotope values that overlapped with values of animals known to be inhabiting dense canopy rainforests, suggesting that they were fully reliant on tropical rainforest resources. This dependence continued through periods of major climatic change, like the Last Glacial Maximum, and even beyond the arrival of agriculture in this part of the island 3,000 years ago. Our work proved that early expanding human populations could live completely in tropical rainforests. Not just that, but they chose to, even when grassland and coastal settings were available nearby. This specialized adaptation was also remarkably resilient, lasting over 30,000 years and perhaps even longer. Tropical Sri Lanka was revolutionizing our understanding of how humans spread so quickly around the world. Unlike many other hominins, they clearly did not always seek out more open, mixed settings, and they certainly did not do everything the “easy way.”11
The next question, then, was what did these humans eat? And how did they get their food? Fortunately, unlike many tropical parts of the world, Sri Lanka had some more gifts to offer global archeology, producing long records of rich organic remains thanks to the cooler conditions inside the caves. Oshan’s recent work, with a number of international partners, has studied the evidence for the technology, plants, and animals found in these archeological sites alongside our specialized ancestors in this part of the world. From the first human arrival in these rainforests 45,000 years ago, these groups were hunting small, fast rainforest animals. Amazingly, monkeys, as well as giant scampering squirrels, with characteristic “cut” and burning marks indicative of human butchery, make up around 70 percent of all mammals found at the sites from 45,000 to 3,000 years ago. Humans were also getting plenty of carbohydrates from the starchy nuts of the Canarium tree and maybe even from wild banana and breadfruit, while snails living in the nearby well-fed streams supplemented their diets. Oshan believes that this evidence shows that “if used the right way and with the right knowledge, tropical forests can be just as rich, if not richer, than dry grassland environments.” In fact, prior to the British colonial period, some groups of the Wanniya-laeto Indigenous population of Sri Lanka still hunted wild forest game, fished, climbed to get honey, and obtained rich sugary plant resources in both the wet and dry tropical forests of the island. These were “forests of plenty,” not barren “green deserts”—particularly for the highly flexible human populations that made them their home.12
The tools left behind by these early human groups in Sri Lanka have also provided a new environmental perspective on some key technologies and innovations associated with Homo sapiens. Bows and arrows and more efficient stone tools have also often been linked to African grasslands or European tundra. But in Sri Lanka, humans were recycling monkey bones to make arrow tips, while tiny “microlith” stone tools may also have been attached to projectile shafts. Similarly, clothing has often been thought of as a clever human adaptation to cold northern European or Siberian temperatures. Again, however, there is evidence of humans working animal skins, perhaps for protection against mosquitoes and leeches (!), 45,000 years ago in humid Sri Lanka. Ochre and shell beads and evidence of long-distance exchange with some human populations on the coast all show a very “human” repertoire of social connection deep in the jungles of this South Asian island. The amazing finds made in the tropical forests of Sri Lanka encourage a more diverse exploration of human dispersals during the late Pleistocene. They show that we can no longer stick to searches on coasts or in temperate and subtropical grasslands. Instead, as in Africa, we should turn our attention to little-investigated, extreme regions to reveal what it truly means to be human.13
MOVING AWAY FROM Sri Lanka, the last decade or so of archeological and anthropological research has begun to show the sheer diversity of tropical forests exploited and occupied by trailblazing groups of humans in late Pleistocene Southeast Asia, Near Oceania, and South America. Southern China is emerging as a potential hotspot for the earliest human fossils outside Africa. Human teeth from two sites with ages clustering around 130,000 to 100,000 years ago (although their true ages remain hotly debated) were found with animals that indicate a mixture of rainforest, mixed woodland, bamboo forest, and grassland habitats. Turning further south and east, some early human teeth on Java and Sumatra from 100,000 to 70,000 years ago have been linked to the expansion of late Pleistocene rainforests in the region, though dating these teeth and determining their relationship to animals found in the same caves is challenging at best, given that these are not archeological sites but rather collections of fossils that are
the product of past flood events that washed them together, postmortem, into the locality. One of the true goldmines of Pleistocene human tropical forest adaptations is the Niah Caves on Borneo. Here, human fossils from 50,000 to 45,000 years ago are clearly linked to the hunting of wild forest boar and primates and the processing of toxic plant foods, all within a unique mixture of Southeast Asian rainforest, swamp forest, and grassland patches that may have been maintained by human hands.14
Unlike Sri Lanka, many early human sites in mainland and island Southeast Asia are linked to a mixture of growing evergreen rainforest and drier woodland habitats. Moving out to sea, into the Pacific, and beyond the famous Wallace Line, the situation becomes more complex. Here, groundbreaking archeologist Professor Sue O’Connor of the Australian National University has been undertaking excavations with Indonesian partners for over two decades. The islands here are generally considered impoverished in terms of animal resources. Never connected to the Southeast Asian mainland, most of these islands were home to no animals bigger than a terrier during the late Pleistocene, presenting a completely new tropical setting for humans to deal with. In fact, Sue’s work on small, isolated islands like Timor and Alor, among others, has suggested that the earliest human groups practiced sophisticated seafaring adaptations. “At the site of Asitau Kuru (formerly Jerimalai) on Timor we have found one of the earliest fishhooks in the world dated to about 20,000 years ago, and in the same site we have evidence for the presence of tuna fish that usually live in open-sea environments dating back to about 45,000 years ago, suggesting that older fishhooks remain to be found,” Sue states. In this case, then, it seems like a reliance on the ocean may have rapidly propelled some of the earliest human groups through this part of the Pacific to arrive in Australia sometime between 65,000 and 40,000 years ago.15
Together, Sue and I performed the same stable isotope analysis on human teeth from these Wallacean sites—the first time this method had been used on Pleistocene hominin teeth anywhere in Southeast Asia. The results initially confirmed what she had expected. The earliest human tooth we had available, dating to 45,000 to 39,000 years ago, showed an isotope value that we would expect from someone eating fish and mollusks from the sea. However, from here things got more complex. During the dry conditions of the Last Glacial Maximum explored in Chapter 2, tropical rainforests retreated in the face of more open, dry forest and grasslands. A return to wetter conditions in the terminal Pleistocene and Holocene saw them rapidly expand. At this point growing human populations seem to have shifted their attention inland. From around 20,000 years ago, the stable isotope data shows that humans were increasingly reliant on these supposedly “impoverished” forest environments. What were they eating? Giant rats appear to be the answer! At around five kilograms, these rodents weighed about the same as an average house cat, and while to us they might not seem too tasty, they would have provided valuable protein. It is also highly likely that poor preservation conditions mean we are missing the large amounts of soft fleshy fruits and starch-rich tubers (i.e., the underground storage organs like we are used to devouring from sweet potatoes) from plants that humans must have used as they sought nutrition beyond the sea. Once again, Homo sapiens, albeit slightly belatedly, found a way to adapt to even the most challenging and isolated of tropical forest environments.16
Figure 6.1. Fishhook made from marine shell preserved at the Pleistocene site of Lene Hara on Timor, Timor-Leste. Researchers believe these same technologies would have been used by humans to capture deep sea tuna from the earliest occupation of this part of the world.
Sue O’Connor
The pattern continues into the frosty mountains of New Guinea. Here, over 2,000 meters above sea level, humans encountered montane tropical forests that can receive snow in winter. Leading experts on the region, like Chris Gosden, have said that during periods like the Last Glacial Maximum, they would have been particularly “cold, difficult, and unpromising” as temperatures fell by as much as 5°C.17 Nevertheless, from 50,000 to 45,000 years ago, a number of sites, particularly within the Ivane Valley of Papua New Guinea, show that early groups of humans occupied the region. Glenn Summerhayes and his team have faced death-defying flights in small planes to try and find the sites, deep in the heart of New Guinea, that allow them to discover how these Pleistocene populations survived under difficult conditions. Using a microscope to explore the soils at these archeological sites, they have found fossil starch grains left behind by carbohydrate-rich yams. Charred, protein-rich Pandanus nuts, apparently cooked by humans on a fire, have also been found at the sites, while the characteristic stone axes found in this part of the New Guinea Highlands have even been associated with the deliberate modification of forests by humans. Alongside the likely pursuit of marsupials in more open settings, humans refined their strategies to survive in these lofty environments.18
Tentative linkage of increasing frequency of charcoal to human arrival and burning of the landscape, as well as archeological evidence for the occupation of cave sites, suggests that humans had reached the dry and wet sclerophyll (a type of vegetation with hard, densely packed leaves along stems that famously includes eucalypt trees) subtropical and tropical forests of northeastern Australia by around 45,000 to 35,000 years ago, though intensive occupation of the wet rainforests of this region seems to have started around 8,000 years ago. After “the Antipodes,” the tropics of Central and South America were the last to be reached by dispersing humans during the Pleistocene. Arriving in the Americas 30,000 to 20,000 years ago, human populations seemingly rapidly dispersed across these regions by around 18,000 to 14,000 years ago, meeting the vast array of environments this part of the world has to offer. In Central America, terminal Pleistocene communities apparently focused on lowland, seasonal tropical forests and dry, cool highland forests. At the famous site of Monte Verde in Chile, humans made use of the diverse dense, temperate rainforest and open, dry forests of Patagonia. By around 13,000 years ago, Homo sapiens had also made it to the rainy, humid evergreen rainforests of the Amazon Basin. Finally, humans reached the supposedly inhospitable montane forests of the high-altitude Andes by 11,500 years ago, adjusting to the Peruvian montane forests and to the low oxygen of heights above 4,500 meters above sea level that has left its mark on the genetic makeup of populations there today. Tropical forests, then, in the Americas and around the Pleistocene world, provide a crystal-clear window into the early human taste for diversity and adversity, rather than monotonous, simple routes of environmental adaptations.19
TROPICAL FORESTS WERE, of course, not the only show in town. Archeologists working in some of the most extreme environments around the world, including deserts, high-altitude habitats, and those beyond the Arctic circle, have all enriched our understanding of the immense threshold of human flexibility during the late Pleistocene. In the Sahara, the Arabian Peninsula, and northern India, human entrances into these modern deserts seem to have been linked to changes toward wetter climates about 100,000 to 70,000 years ago. However, in the Kalahari and Namib Deserts of southern Africa and the Central Deserts of Australia, Pleistocene humans seem to have also prospered under dry conditions with limited water. By 80,000 years ago, humans had adapted to the cold, patchy environments of the African “Mountain Kingdom” of Lesotho as well as the highlands of Ethiopia, and by 40,000 to 30,000 years ago, they had even reached the icy Tibetan plateau. Bones with cutmarks found at the 72nd parallel north even tentatively show the advance of humans into the Arctic Circle by 45,000 years ago. Of course, Homo sapiens used savannahs and coastal settings as well. They would have been foolish not to. But all of the above evidence, like the diverse tropical forest examples we have seen, show that our species was not a one-trick pony and was, almost literally, everywhere by the close of the Pleistocene.20
Figure 6.2. Map showing the dates of earliest occupation of different tropical forests by Homo sapiens during the late Pleistocene.
With this in mind, the new technologies, new social capacities, new
ornaments, new cultural materials, and new exchange systems and ways of passing down knowledge that are often considered uniquely “human” are best seen as a wide-ranging catalog for dealing with diversity rather than a one-size-fits-all tool for a single habitat. The advantage is obvious. Different, growing communities, all specializing in very different environments, meant that the fluctuating climates of the late Pleistocene would be highly unlikely to affect Homo sapiens at the species level. Populations of our human ancestors almost certainly disappeared locally (or were “extirpated”). In the Levant, for example, early evidence for human arrival from Africa between 200,000 to 100,000 years ago is followed by a marked absence until around 43,000 years ago. However, seemingly unlike the Neanderthals, the Denisovans, the “Hobbits,” and Homo erectus, the overall human population generally kept growing, with communities in certain environments picking up the slack when other environments turned hostile. Using personal ornaments and social networks to communicate between populations inhabiting very different environments provided a crucial social fallback in times of stress. In this way we survived and also continued to expand. With greater populations and greater numbers in different parts of the planet, we began to interact more intensively with the natural world, finding new, more manipulative ways of feeding ourselves and buffering the unpredictable Pleistocene world we had been born into. By the fall of the Pleistocene curtain, we had adapted to all of the land-based environments the world has to offer. What we did next would change them forever.21