Grass: In Search of Human Habitat

6. Where the Short Grass Grows

S I X Where the Short Grass Grows 31 Figure 6. Pronghorn antelope on shortgrass prairie. Photo by author. Mike Rose claims the ability to envisage the natural human habitat on the basis of the last bone in the big toe. Mike lives with his wife, Cordelia, on a shortgrass mesa just north of the small town in which I live. From their yard the view sweeps 360 degrees to horizons of near and far mountains, giving the impression of standing on a platform at the edge of a huge, shallow bowl. The night darkness, punctuated only occasionally by artificial light, stretches pregnant with prospect in all directions. The word savanna best describes the hillsides and valleys that drop from the edge of the Roses’ mesa. Grasslands dotted with juniper, scrub oak, and pinyon pine roll away to the north, the west, and the south. The Mogollon Mountains rise to the east. A photo composite attached to an inside wall of their house shows a landscape of Kenya in East Africa. “One reason we retired here,” says Cordelia with the British precision of speech she and Mike share, “is that it feels like Kenya. It reminds us of the years we worked there.” Our town occupies that part of the American West inhabited by foreseers and prophets of the intuitive kind. You might therefore conjure up an image of Mike rattling toe bones in a small cup and casting them, like dice, onto a Navajo blanket, then examining them for clues—looking for magical insight into the natural human habitat. But I have not known Mike to call upon clairvoyance. He is an anatomist and student of skeletons. For years, twelve in East Africa, Mike studied the bones of primates— humans, apes, monkeys, and their relatives. He retired from his university position in 2005. In early 2006 he and Cordelia went away for several days to Duke University, to a symposium held in his honor, a testament to his standing among those who study such things. “The distal bone in your great toe,” Mike says, “shows anatomical features peculiar to long-distance striders.” These features show people to be the only living primates built for walking. Other primates have toe bones that look different; their feet, and the bones in them, serve best for climbing trees, not walking upright. The gorilla, the orangutan, and our closest relative, the chimpanzee, all live in forests. The human foot evolved in grasslands. “My friend Rick Potts,” he said, “recently published a book about human ancestry. You may want to read it.” Potts’s book appealed to me right 32 away because of the foundation of his knowledge: years spent digging in the Rift Valley. He knew the habitat first-hand. In this region of East Africa, says Potts, we find the oldest-known signs of humans and near-humans. Here lies the story of our ancestors. Potts offered insight into a question that had long intrigued me. At what point did evolution propel us from the line of the ancestral “ape-man” onto the tangent that made us human? Potts has a definite opinion: it happened when we left the trees and strode erect across the grass, when the bones of our legs lengthened and those of our feet relaxed and arched away from the curling grasp of tree climbers. In that faraway time we became hominids—members of the human family. How long ago did this happen? Three to four million years, maybe longer, say the ancient bones and tracks. Potts notes several early hominid finds: Meave Leakey’s Australopithecus anamensis from northern Kenya, Donald Johanson’s well-publicized “Lucy” from Ethiopia, and Mary Leakey’s upright strider’s tracks preserved in volcanic ash in Tanzania. Some scientists see in these and similarly aged bones a residual dependence on trees, he said. This is not surprising, however, considering the typically slow, transitional nature of evolution. Potts elaborates on what he and other anthropologists call the “savanna hypothesis,” the notion that the drying out of East Africa’s climate several million years ago, and the resulting change from forest to savanna, opened the way for an upright ape. Potts takes the idea further, arguing that not simply the increasingly arid environment but also repeated shifts in climate and habitats opened the way for a physically adaptable and problem-solving being—our ancestor. He puts it succinctly: “Adaptation to open...