floor of the Atlantic, as well as an abyssal fan, a river delta composed of millennia of sediment, hidden beneath the ocean.
But the landscape where I found myself listening to roosters crow across Djolu’s clustered homesteads is more ancient than much of the rest of Africa. The Congo basin is a craton, an ancient continental core dating back 2 to 3.6 billion years. Whereas much of the earth’s crust is composed of relatively new material from plumes and rifting, cratons are typically thicker and deeply rooted, resistant to volcanism, which will occur at their edges but not their centers. While the lands of Africa swelled and broke open around it, the Congo craton held its place. East Africa lifted, drying out and losing its forests as it gained altitude, but the Congo remained lush. The waters drained from the newly raised lands, pouring into the low, immovable basin and making it one of the wettest places in Africa. Today, most of the DRC lies within what Alden Almquist, in Zaire, describes as a “vast hollow . . . the shape of an amphitheater, open to the north and northwest and closed in the south and east by high plateaus and mountains.”
When the glacial cycle started in the Northern Hemisphere, a brief 2.6 million years ago, trapping vast quantities of the planet’s moisture in polar ice, many African rivers, the Nile among them, ceased to reach the ocean, and the tropics withered. The Congo basin was one of the few areas to retain some of its rainforest. Though great apes likely died off elsewhere on the continent, small groups of them could have survived here.
As early as six million years ago, in the long cooling period leading up to our current ice age, our earliest ancestors became increasingly bipedal, spending more time on the ground. However, the severe changes caused by glaciation coincided with a rapid spurt in evolution that may have given rise to modern humans. The situation could have been similar to that of the earlier apes, only more extreme: the drying eliminated trees and created a hostile environment with few resources. Paleontologist and anatomist Kevin Hunt argues that as trees became much smaller and branches thinner, early hominids found that foraging by climbing was increasingly difficult; instead, they often stood on the ground and reached up for the fruit. Supporting this theory is the observation that today, among chimpanzees, tool use, carrying food, confrontational display, and looking over obstacles account for only 1 to 2 percent of bipedal behavior, whereas feeding, most often from the low branches of small trees, accounts for 85 percent of it. Again, if the environmental conditions were harsh, a bottleneck might have occurred, many of the early hominids dying off, leaving only those who were adapted to the new circumstances and capable of using bipedalism to their advantage, not only for foraging but also for hunting. Those human ancestors who could walk upright also used less energy during travel and freed up their hands to carry food, thereby nourishing themselves even when they couldn’t forage successfully. They could also move between distant patches of forest more readily, and, as a result, provision more offspring.
In Catching Fire, Richard Wrangham offers an analogy to evoke the close bond that humans share with these early hominids. He gives the example of an australopithecine, an ancestor of modern humans that lived three million years ago, approximately halfway along the evolutionary path from our last common ancestor with chimpanzees and bonobos:
Imagine going to a sporting event with sixty thousand seats around the stadium. You arrive early with your grandmother, and the two of you take the first seats. Next to your grandmother sits her grandmother, your great-great-grandmother. Next to her is your great-great-great-great-grandmother. The stadium fills with the ghosts of preceding grandmothers. An hour later the seat next to you is occupied by the last to sit down, the ancestor of you all. She nudges your elbow, and you turn to find a strange nonhuman face.
As for all of the grandmothers going back to the last common ancestor of humans, chimpanzees, and bonobos, it is conceivable that they could be housed in the United States’s largest stadium, that of the University of Michigan, which hosted a record 114,804 attendees in 2011. In Richard Dawkins’s essay, “Gaps in the Mind,” he describes a similar thought experiment and writes that, in the lineage leading back to the last common ancestor, “you would nowhere find any sharp discontinuity. Daughters would resemble mothers just as much (or as little) as they always do.”
Recent research suggests that there were numerous species of early humans, often overlapping or being rendered extinct as they spread out. Homo sapiens—modern humans—originated in Africa sometime before two hundred thousand years ago, then moved into Europe, killing off or absorbing the Neanderthals, adept dwellers of cold climates whose cranial cavity, despite our image of them as brutes, was in fact larger than our own. The Neanderthals left a significant trace of their DNA in humans living outside Africa (about 2.6 percent in mine, according to a genetic test), but Homo sapiens endemic to the Congo have no trace of Homo neanderthalensis in their genes. Nor do they, the Europeans, or Asians, have the genes of Denisovans, hominids living in Siberia forty to sixty thousand years ago, though the Melanesian and Australian aborigines share about 3 percent of their DNA with them. Numerous tribes of early human species likely dotted the earth, interbreeding and gradually forming our own species as we now know it.
Unlike in other parts of Africa, where volcanic activity has preserved traces of ancient peoples, the Congo rainforest leaves few fossils. Though migrations have crisscrossed the region, the soil of the forest is high in acidity, dissolving bones. What we know of human history here is limited. Before the arrival of the current racial majority, the Bantu, the likely inhabitants were pygmies, people thought to have evolved smaller because of forest conditions. Modern-day pygmies use non-Bantu words for many aspects of the forest and its plants, but speak languages derived from their contact with the Bantu, who spread from Cameroon and eastern Nigeria three thousand years ago. Empowered by Iron Age technology, the Bantu moved out in successive waves over centuries, in one of the largest expansions in human history.
Today, there are over seven billion humans, and no other mammal species can claim our rate of successful adaption. As Dale Peterson writes in Eating Apes, a book that describes some of the failures of major conservation NGOs and the degree to which logging and the commercial bushmeat trade are decimating great ape populations, “we are growing rapidly enough to displace, body for body, the entire world population of chimpanzees every day; rapidly enough to displace, body for body, the entire world population of gorillas every twelve hours; and rapidly enough to displace, body for body, the entire world population of bonobos every six hours at least.” The destruction of other creatures’ habitats has allowed this, though increasingly we are looking for other ways of living, our self-awareness being the trait that can most help us as our climate again changes and we question the future of our resources. In the process of trying to understand ourselves, we have become fascinated with our origins. But if we want to reconstruct the path of human evolution, the best way for us to understand what is lost or left only as rare, incomplete fossils is to consider the great apes, our closest cousins who are hunted to the verge of extinction. Though the reduction of great ape habitats likely began thousands of years ago as a result of human expansion, farming, and hunting, various factors have caused it to speed up exponentially. Booming human populations fuel the demand for timber and bushmeat, and modern weapons and motorized transportation facilitate their extraction. Even though laws forbid great ape hunting throughout Africa, they are rarely enforced, and few people know about them. Furthermore, as a result of both the local and global demand for palm oil, which is found in many Western household products, plantations are being created across Africa, resulting in massive habitat destruction. Lastly, the international race for mineral resources has funded the recent wars here, displacing communities, destroying the infrastructure, and forcing millions of people to rely on bushmeat to survive.
I was only beginning to grasp how the rainforest had shaped these people. It was a world of close horizons, walls of trees blocking my sight, the earth itself suddenly rising or falling, so that paths had to wind constantly around obstacles. Ever since I was a child, I’d thought in landscapes. I loved photographs of mountains, deserts, or plains, rolling hills or savannah, and only after staring at them for some time did I feel that I was ready to learn about their inhabitants, that I might understand them. But this terrain was unlike any I had known, and since our landing the day before, it seemed to me that the rainforest had absorbed the past, dissolved it like ancestral bones, and it would take time for me to begin to comprehend the culture here in deeper ways.
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