Worth Reading: The Ape in the Tree

Charles Fergus
December 03, 2007

Married co-authors Alan Walker and Pat Shipman write in their new book The Ape in the Tree that humans are separated by "at least one million generations" from a creature known as Proconsul, which evolved in Africa during the Miocene era between 21 and 14 million years ago. Proconsul was a 20-pound primate that lived in trees and ate fruits. We know it from a wealth of fossils found at several sites, including ones on Rusinga and Mfangano Islands in Lake Victoria, Kenya, where Walker led a series of archaeological expeditions during the 1980s.

The extinct genus Proconsul was named, rather whimsically, for a series of performing chimpanzees who were all given the name "Consul" (much the same way that most elephants were called "Jumbo"). Around the turn of the twentieth century, these chimps entertained audiences in Europe and Britain by playing the piano, riding a bicycle, smoking cigarettes—all while wearing human clothes. The ancient Proconsul ("before Consul") was, Walker and Shipman believe, "the last common ancestor to whom we—humans and apes alike—all trace our past."

Walker, a paleontologist at Penn State, and Shipman, an anthropologist and a professional science journalist, have long been intrigued by Proconsul. As a graduate student in England during the 1960s, Walker helped his faculty advisor analyze its bones, particularly the limbs, and compare them with skeletal features and modes of locomotion in modern primates. They deduced that Proconsul was a "powerful, fairly slow-moving animal that spent most of its time in the trees, moving both on all fours and also hanging from branches."

orange book cover
John Gurche

The Ape in the Tree: An Intellectual and Natural History of Proconsul

Later, as a professor at universities in Uganda and Kenya, Walker worked with Louis Leakey and his wife Mary; the Leakeys had discovered many Proconsul fossils in the 1930s and 1940s, including a nearly complete skull. The Ape in the Tree offers a clear-eyed assessment of the Leakeys, particularly of Louis, a pioneering anthropologist who, while contributing much to our understanding of primates, was wont to trumpet his own finds (and only his own finds) as direct human antecedents. Leakey was interested mainly in later primates, particularly tool-using ones. He was also somewhat disorganized. Leakey overlooked many Proconsul fossils and misidentified others as coming from primitive pigs, crocodiles, and turtles. Over the years, Walker rounded up those wrongly labeled specimens (he calls it "excavating in a museum"). He also studied old field notes and diaries, then returned to Kenya and located the waste material at an early site, "backdirt" that the Leakeys had excavated but had deemed "not worth taking." There Walker found Proconsul teeth, jawbones, and many other bone fragments.

Consolidating the scattered fossils, Walker filled in existing partial skeletons. He and his graduate students—first at Johns Hopkins, then at Penn State—collaborated with scientists across a range of disciplines, men and women working in museums, hospitals, and universities around the world. They used techniques such as DNA sequencing and single crystal laser fusion dating to create a clearer and more complete picture of Proconsul, including the evolution and the probable behavior of this important "stem ape."

Over time, Walker was able to show that Proconsul was still evolving the slowed pattern of maturation and development that is typical of modern apes; that it did not have a tail (modern apes lack one, whereas today's monkeys retain a tail); and that it had a flexible back, a trait that monkeys have carried on but that apes have lost. At one site, Walker found a wealth of bones in a column of distinctive rock. He deduced that a large forest tree had died and been buried by volcanic ash. After the tree's trunk rotted, carnivores took up residence in the convenient den. They brought in prey animals, including many Proconsul meals. Those and other fossils "represented a local animal community that lived near the tree," write Walker and Shipman. From this important assemblage, "we could build a detailed and accurate picture of the ecology of the area as well as of the species Proconsul itself."

ape skull
Alan Walker

The original Proconsul skkull was found in 1948. Additional pieces found in museum collections more than 30 years later glued perfectly (right lateral view).

Throughout their book, Walker and Shipman weave stories into the science. Stories of monumental African thunderstorms that rip apart tents and wash away specimens. Truculent hippos that want to overturn boats. Negotiations with local chieftains and farmers on whose lands the scientists wish to dig. Silent nomads who, with their rusting antiquated rifles, watch from the shadows of the bush. The narrative includes historical accounts of how earlier geologists and paleontologists made the first Proconsul finds (one unlucky seeker got eaten by a crocodile after a hippo swamped his boat), and thumbnail sketches of the brilliant and sometimes erratic scientists with whom Walker has collaborated in trying to understand "the ape in the tree"—the ape in our human family tree.

As an anthropologist, Walker aims "to bring the past back to life, to envision and understand the biology of the past as well as I can that of the present." He strives to create "a colorful, detailed, and rich image of what the world was once like." He and Shipman have succeeded in doing so, both through their science and in this compelling, well-written book.

Alan C. Walker, Ph.D., is Evan Pugh professor of anthropology and biology in the College of the Liberal Arts and the Eberly College of Science, axw8@psu.edu. Walker is a Fellow of the Royal Society, a member of the National Academy of Sciences, and the recipient of a MacArthur "genius" award. Pat Shipman, Ph.D., is adjunct professor of anthropology, pls10@psu.edu, and a Fellow of the Royal Geographic Society and the American Association for the Advancement of Science. The Ape in the Tree: An Intellectual and Natural History of Proconsul, was published by Harvard University Press in April 2005. Charles Fergus is a freelance writer in Vermont.

Last Updated December 03, 2007