The Wisdom of the Bones


May 10, 2007

Teaser: By Alan Walker and Pat Shipman

Nariokotome is not a word that flows trippingly off the tongue, and you won't find it easily in any ordinary dictionary or atlas. But to students of human evolution it is the place in northern Kenya, west of Lake Turkana where an astonishingly complete 1.6 million-year-old juvenile Homo erectus skeleton was discovered in 1984. After several field seasons of demanding excavation, and during the following decade of detailed laboratory research in the able hands of Alan Walker, this specimen, catalogued as KNM-WT 15000, provided valuable insights into the anatomy and adaptations of a distant human ancestor. This meaty book, written by Walker and his wife Pat Shipman, chronicles the amazing journey of discovery from the original find to the publication of a landmark monograph on what is sometimes referred to as the Turkana Boy.

For two weeks Kamoya Kimeu, leader of the famed fossil hunting team dubbed "The Hominid Gang", had been searching the hostile and desolate landscape, where temperatures reach 135 degrees, looking for fossil hominids, those important pieces of the puzzle which bring us enlightenment about our origins. Unusual for him and his team, not even the tiniest fragment of a fossil hominid had come to light. Frustrated and disappointed he decided to have one last look, because unlike many other fossil hunters, Kamoya never gives up, his success is a direct result of unexcelled perseverance.

Alan Walker, a paleoanthropologist/anatomist and famed fossil hunter, Richard Leakey, have long collaborated in the quest for clues to our ancestry, and the recovery of the "Turkana Boy" constitutes one of the most significant finds in their careers (and indeed in paleoanthropology itself). The skull, for example, is sufficiently complete to yield an adult brain size of 909 cc which in combination with body size and stature estimates permitted evaluation of relative brain size and growth and development. Although 900 cc is considerably larger than the average of 650 cc for earlier Homo habilis skulls, the large stature of 15000 (15K) meant that relatively speaking this was not much of an improvement.

The exceptional completeness of the postcranial skeleton, including rare elements like the ribs, allowed Walker and his collaborators to gain insight into locomotion, maturation, gestation, limb proportions, body shape, and even the language abilities of this species. After digesting this rich book, the reader comes away with such a detailed appreciation of this 1.6 million-year-old ancestor; it virtually comes to life.

The opening chapter relates the excitement of discovery and the team's intense commitment to recovering every splinter of bone, every chip of enamel of this important skeleton. Excavation revealed that the boy died, perhaps from a dental abscess, and slowly decomposed in a shallow, reedy swamp, was trampled by a hippopotamus (today hippos are responsible for more human deaths in Africa than any other any animal), and before scavengers could feast on the skeleton, it was quickly covered by silt, and ultimately fossilized.

Three delightful and highly informative chapters relate earlier attempts to discover the "missing link", a term of which Walker writes, "is an artificial construct and an unholy grail." Probably Many readers will be surprised to learn that it was Ernst Haeckel, a biologist and popularizer of science, who first coined the term "missing link" in 1868 and predicted that it would be found in Asia. In his hypothetical tree of life he inserted the name Pithecanthropus alalus, the "Speechless man ape". Inspired by this prognostication, the Dutch physician, Eugene Dubois, traveled to Java, discovered a skull cap and associated femur (some think the femur is actually of a modern human), which he dubbed Pithecanthropus erectus, now called Homo erectus.

The discovery of further specimens in China by the Canadian anatomist Davidson Black, who was found dead one morning, hunched over a skull he had been studying, and Franz Weidenreich's subsequent work make for fascinating reading. What emerges from this historical overview is that if you find the "missing link", beware. Dubois had a nervous breakdown and dropped out of science because his European colleagues criticized him so strongly. Let's not forget what happened to Black and when Weidenreich attempted to protect the Chinese fossils from Zhoukoudian in the face of invading Japanese troops, the entire collection was lost to science (interestingly on December 7, 1941, Pearl Harbor Day) somewhere between Beijing and the China Sea where they were scheduled to be placed aboard an American ship. Thus far, Walker has faced no ill-luck, but he remarks that finding great fossils "may bring acclaim or scathing disregard, fame and fortune or illness and death" but "you will not suffer from boredom."

The fascinating details, found in the last seven chapters, of The Wisdom of Bones, constitute some of the best paleo-detective writing available. Readers are urged to devote a little extra time for wading through the seemingly more technical sections, because it is here that one gains a real appreciation for how seemingly minor details of anatomy become so vitally central to reaching important conclusions about the Nariokotome skeleton.

Determination of the biological age of death of the Turkana Boy proved to be more complex than simply looking at the state of dental eruption and comparing it to modern humans of known age. Certain aspects such as the late eruption of the canine teeth suggested that maturation was not like that of an ape, but on the other hand the molar teeth appeared to have erupted earlier than in a modern human. Based on a human scale of body growth and tooth eruption the boy's age was estimated to be between eleven and fifteen year's old at death, but using an ape scale an age at between seven and nine years is suggested. In addition to the dental data, one of Walker's co-researchers, B. Holly Smith, considered bone growth and brain size (880 cc at death) and concluded that the Turkana Boy grew up on a time scale halfway between chimps and humans, concluding that he probably died around age ten, a young adolescent.

Observing modern human populations reveals that those who live in areas of high ambient temperature have long, slender limbs which increases the surface to body mass ratio, promoting heat dissipation through perspiration. Human groups like the Eskimo, who live in areas of low ambient temperature have short limbs and tend to have low surface area to body mass--their bodies are heat conservers. Walker and his colleague Christopher Ruff, for a number of reasons, including the knowledge that the Turkana specimen was from a tropical area, used stature data and growth trajectories based on living Nilohamitic tribesmen from Equatorial eastern Africa. Employing length measurements of the femur and tibia (a high correlation exists between these bones and stature), the adolescent boy stood five feet, three inches (1.6 meters) but would have been an astonishing six foot one inch (1.85 meters) adult.

Employing information of the body weight for Nilohamitic peoples, they furthermore calculated that at the time of death the boy weighed 106 pounds, but would have been closer to 150 pounds as an adult. All of this, combined with observations of a very narrow pelvis gave the impression of a "beanpole of a man." Even more interesting is the observation, made by Ruff, that the body, using the pelvis as measure of width, is a cylinder, and the shape of the cylinder is closely correlated with mean temperature. Applying this knowledge to the Turkana specimen suggests that he lived in area with a mean ambient temperature or roughly 86 degrees, very similar to that of the Turkana region today!

This book abounds with many examples of clever anatomical detective work, which flesh out a myriad of behaviors and adaptations of the Turkana Boy. I will only mention one more, which in a way was what Haeckel had predicted over a century ago. A vertebrae specialist, Ann MacLarnon observed that canal for passage of the spinal cord is relatively small (compared with our own) in the thoracic vertebrae. She surmised that the Turkana Boy had less neural enervation for regulating the passage of air in and out of the lungs. Lack of precise control of the breath, she and Walker surmised, rendered the boy, speechless.

Perhaps not everyone will agree with the taxonomic assignment of the Turkana specimen to Homo erectus. For an increasing number of anthropologists (including myself), 15K makes an excellent evolutionary antecedent to Homo erectus, as is known from Asia, but differs in a number of anatomical features which justify placing the boy in another taxon, dubbed Homo ergaster. Walker and Shipman note that perhaps specimens assigned to Homo habilis, especially, but not exclusively those from Olduvai Gorge, have australopithecine like body proportions (relatively long arms) and may not be ancestral to later hominids like 15K. They suggest that we must look elsewhere to skulls like the well-known KNM-ER 1470, which have been assigned to yet another species, Homo rufolfensis, for an ancestor to the Turkana specimen. While definitive evolutionary relationships between what is appearing more and more to be an increasing complexity in early Homo, the knowledge gained from KNM-WT 15000 strongly suggests that only with additional, similarly complete specimens, will this muddle be sorted. Until such a time, anthropologists should remain flexible and uncommitted to a particular evolutionary interpretation. We should, however, harbor hope that teams like "The Hominid Gang" will make more discoveries that will divulge as much "wisdom" as the young boy from Nariokotome.

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Donald C. Johanson

Founder and currently Director, Institute of Human Origins,Virginia M. Ullman Chair in Human Origins Professor School of Human Evolution and Social Change, Arizona State University