Unlike our ape cousins, we have evolved a dependency on physical activity. Current advances are overturning that view, showing how humans have changed physiologically as well. But they have generally assumed that these were changes in shape and behavior, not in the fundamental function of our cells. For decades researchers have known that this last chapter of our evolution was marked by major anatomical and ecological changes-among them, ballooning brain size, hunting and scavenging, increasingly complex stone tools and larger body size. Discoveries from fossil excavations, zoos and laboratories around the world are revealing just how radically our bodies changed over the past two million years. But living apes provide the best chance to see where we came from and to understand how much of us is ancient and unchanged.Īnd yet it is the differences, rather than the similarities, between humans and apes that are casting new light on the way our bodies work. No species alive today is a perfect model of the past-all lineages change over time. And the further back in time we go in the fossil record, the more apelike our ancestors look. The kids learn from their mothers, wrestle and play with one another, and throw tantrums. Some will kill their neighbors over turf and hunt other species for food. Apes are clever, use tools, fight and make up, and sneak off to have sex. It is not just that we share more than 97 percent of our DNA with orangutans, gorillas, chimpanzees and bonobos. People are drawn to apes because we see so much of ourselves in them. Only recently have I come to appreciate what ape idleness tells us about human evolution. But as I settled into the rhythm of fieldwork that summer, following chimpanzees from dawn to dusk, I came to a very different conclusion: chimpanzees are lazy. Months earlier, while mulling over summer research plans from the comfort of my desk at snowy Harvard University, I envisioned chimpanzees waging a heroic struggle for existence, working hard on a daily basis to eke out a living. It seemed to me that the energy spent climbing might be a critical factor in chimpanzee ecology and evolution, shaping their anatomy to maximize climbing efficiency, thus sparing calories for reproduction and other essential tasks. student studying human and ape evolution, I was in Kibale National Park that summer to measure how much chimpanzees climb each day. Now at our destination, the lights were off, and we stood there silently, submerged in a black ocean of forest, the surface 30 meters above, listening to the chimps chuffing and shifting in their leafy nests.Īs a young Ph.D. Our team of three researchers and two field assistants had woken up an hour before, wiggling into rubber boots and hastily assembling backpacks before setting out on muddy trails by headlamp. In the predawn damp of a Ugandan rain forest nearly 20 years ago, I stared up through the crowded canopy at a party of eight chimpanzees sleeping overhead.
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