About Turkana Boy

Age, life, and death of the Nariokotome Homo erectus (KNM WT-15000)

In 1984, Kamoya Kimeu, legendary fossil finder working for paleontologists Mary and then Richard Leakey in Kenya’s Lake Turkana Basin, spotted a section of skull on the shore of a dried-up riverbed, the Nariokotome. Patient and careful excavation revealed all but the feet of a 1.5 million year old skeleton. The boy the skeleton belonged to had shoulders, arms and legs that more closely resembled those of a modern human, so the skeleton was named “Turkana Boy”. His age, at the time of his death, was hard to pin down. Certainly, the lower jaw had incisors, canines and first and second premolars partially erupted, with third molars absent. The upper jaw still had milk teeth canines, with most of the permanent teeth partially formed. The features matched the tooth development of an 11-year-old boy.

His bones were still forming; the centers of formation on either side (epiphysis) had not fused in the middle of his long bones: his arms, legs and hips. This was further evidence that the boy was about 11. From the length of his thigh bone, we could tell he was about 5’3”. From the breadth of his bones, he must have weighed around 103 pounds. Modern human growth curves don’t really apply. Turkana Boy’s projected growth was recently recalculated using growth curves between human and ape norms. We now think he was around 9, beginning to experience a short adolescent growth spurt relative to ours that would have seen him grown (5’4” tall) by age 12.

How did he die? Two root fragments from a broken milk tooth, his second molar, caused an infection under pressure from his erupting premolar, and septicemia, blood poisoning, leading to an early demise. His body, sandwiched between two layers of volcanic ash half a million years apart, became exposed, with erosion, 1.5 million years later.

A boy with a head of hair, rather than fur-covered, whose proportions—arms, shoulders, chest and legs, resembled those of modern humans. He was named “Turkana Boy”. Overlapping with the australopithecines and an intermediate hominid form Homo habilis, Turkana Boy was exciting for multiple reasons.

To understand the significance of Turkana Boy, consider the most famous discovery at the time, from Hadar in Ethiopia, made by Paleoanthropologist Don Johanson’s team, an assembly of bones of a female australopithecine that was named “Lucy.” Lucy lived 3.2 million years ago. Her arms were long, and massive, her chest, funnel-shaped, like a chimpanzee’s; her fingers curved, like those of all tree-climbing primates. She spent at least a third of the time climbing trees, using enormous upper body strength. On the other hand, her feet, knees and hips, even the position of her head on her neck, were clearly adapted for a very rare trait in mammals, walking on two legs. Wide hips and lower rib cage framed a big belly that held a large gut, adapted to produce fat by fermenting a fibrous diet. Her gut, and the energy consumed to process the rough diet, made for a slowed gate. Her brain was one-third the size of the modern human brain, roughly on par with a chimpanzee’s.

The discovery of Turkana Boy tells us that a later protohuman form existed, barrel chested, rather than funnel-chested like Lucy, with a tucked-in pelvis, six vertebrae in the lower back (96% of humans now have 5) clearly evolved for walking, Homo erectus. His hands were free, as he walked, which suggests that he may have been able to carry a spear. This would have been useful. The landscape around Turkana Boy was shifting, forest cover giving way more often to open savannah, where, visible to predators, he would need to defend himself and compete for meat, fighting over scraps left by lions, ambushing animals, eventually actively hunting. A drop in the number of carnivore fossils around the same time suggests that his kind were successful competitors. The discovery of a group of male footprints suggests the formation of male social groups hunting among males targeting high-risk prey. Smaller teeth and jaws, smaller chewing capacity overall suggest Homo erectus ate meat balanced with a high-quality plant diet of berries, seeds, nuts, insects and grubs, tubers, bulbs and honey. Male hunters and female gatherers may have paired up. On the open savanna, encounters with natural fires would be frequent, and there is evidence that Homo erectus controlled fire and cooked, releasing more nutrients from food and making meat more digestible. A high quality diet of 50% meat meant that energy produced, particularly in the consumption of animal fat, could be diverted to brain growth over time.

His smaller vertebrae would have wrapped around a narrower spinal cord, which could not have handled control of his lung capacity to his mouth to form speech. The inside of his skull (endocast) shows traces of what would become our speech center, an asymmetry in extra space of the left brain that is longer than the right. One theory suggests this extra space was dedicated to motor movement programs that later provided the underlying structure for language, motor programming associated with the human preference for right handedness (75-90% of modern humans anywhere are right handed). Turkana Boy’s brain, larger than any before him, was about two-thirds the weight of our modern brain, so his behavior was probably very different from ours (in comparison, a two-year-old has 80% of the brain size of an adult). He could have been an accomplished tool user, and maybe a hunter, whose people made large and small stone tools, particularly, hand-axes for scraping meat off the bones of dead animals in a climate as hot as it is today in the Turkana Basin (average temperature).