|Catalog number||KNM-WT 15000|
|Common name||Turkana Boy, Nariokotome Boy|
|Species||Tentatively assigned Homo ergaster|
|Place discovered||Lake Turkana, Kenya|
|Discovered by||Kamoya Kimeu/Richard Leakey|
Turkana Boy, now called, Nariokotome Boy, is the common name of fossil KNM-WT 15000, a nearly complete skeleton of a hominid who died in the early Pleistocene. This specimen is the most complete early human skeleton ever found. It is believed to be between 1.5 and 1.6 million years old.
His age has been estimated from 7 years six months to as old as 15 years. The most recent scientific review suggests 8 years of age. It was initially suggested that he would have grown into a 1.85 m tall adult but the most recent analysis argues for the much shorter stature of 1.63 m. The reason for this shift has been research showing that his growth maturation differed from that of modern humans in that he would have had a shorter and smaller adolescent growth spurt.
Adolescence and maturity
The shape of the pelvis identifies that the specimen was a male. His estimated age at death depends upon whether the maturity stage of his teeth or skeleton is used, and whether that maturity is compared to that of modern humans or chimpanzees. A key factor here is that while modern humans have a marked adolescent growth spurt, chimpanzees do not. While initial research assumed a modern human type of growth, more recent evidence from other fossils suggests this was less present in early Homo. This affects the estimation of both his age and his likely stature as a fully grown adult.
- Anthropologists Alan Walker and Richard Leakey in 1993 estimated the boy to have been about 11–12 years old based on known rates of bone maturity.[nb 1]
- Christopher Dean (M. C. Dean) of University College London, in a Nova special, stated that Turkana Boy was 8 years old at death. Alan Walker and Richard Leakey, though, explain that dental dating often gives younger than actual ages.[nb 2]
- Ronda Graves and colleagues in the most recent review of the problems involved conclude that he would "have grown an additional five to 14 cm before reaching adulthood" and that "if, at death, he was eight to ten years of age, [he would have been] 154 cm tall, and growing faster than a modern human but slower than a chimpanzee. According to this scenario, KNM-WT 15000 would have attained an adult stature ranging between 159 cm and 168 cm." Moreover that "according to our preferred models of growth and development, [his] growth in stature [would have been] completed by 12 years of age (4 years after death), so that the majority of growth has already occurred.
The specimen comprises 108 bones, making it the most complete early human skeleton discovered. The skeleton is about 1.60 m (5 ft 3 in) tall. In adulthood, Turkana Boy might have reached 1.85 m (6 ft 1 in) tall and massed 68 kg (150 lb). The pelvis is narrower than in Homo sapiens, which is most likely for more efficient upright walking. This further indicates a fully terrestrial bipedalism, which is unlike older hominid species that show a combined feature of bipedalism and tree climbing. The Boy was relatively tall, which increased his body surface area that would enhance heat dissipation and prevented him from overheating under the hot sun.
The overall KNM-WT 15000 skeleton still had features (such as a low sloping forehead, strong brow ridges, and the absence of a chin) not seen in H. sapiens. However, there are significant defining characters, such as bigger brain size (880 cc). The arms and legs are slightly longer indicating effective bipedality. The nose is projecting like those of humans rather than the open flat nose seen in apes. Body hair may also have been thinner (most likely naked) and possibly with increased sweat glands to hasten cooling. The skin also was most probably much darker with abundant melanin, as it was necessary to cope with the direct tropical sun rays in the African savannah.
The fossil skeleton and other fossil evidence such as Acheulean stone tools prompt the majority of scientists to conclude that Homo ergaster and Homo erectus – unlike their more primitive ancestors – became efficient hunters. The social structure would probably have become more complex with a larger brain volume; the Broca's area of the brain allows speech and is noted by a slight slant on the cranium. Turkana Boy's thoracic vertebrae are narrower than in Homo sapiens. This would have allowed him less motor control over the thoracic muscles that are used in modern humans to modify respiration to enable the sequencing upon single exhalations of complex vocalisations.
It has been suspected that Turkana Boy suffered from a congenital disorder, either of dwarfism or scoliosis. This was because the rib bones appeared asymmetrical to the spine and the reason was attributed to skeletal dysplasia. However, in 2013, a new study shows that when the rib bones were carefully rearranged, it became symmetrical against the spine, and that unusual structure of the vertebrae was characteristics of the early hominins. However, the fossil definitely showed lumbar disc herniation, an injury implicated with his death. He also had a diseased mandible.
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- Walker explains: "in KNM-WT 15000, his skeletal development can only be used to place an upper limit of about 14 years on his age at death. However, a less often recognized skeletal maturational event does generally occur prior to 14 years in modern males-- the union of the trochlea and capitulum (and also the lateral epicondyle) of the humerus, prior to their joint union with the humeral shaft.... That these elements were fused in KNM-WT 15000 (at least the capitulum and trochlea) suggests a skeletal age for him of somewhat more than 11 years.... In either event, 11 to 12 years would seem to be the best compromise figure to use for his chronological age at death."(Walker & Leakey, 1993, p. 235)
- "Just as in the case of human dental age (above), estimates based on tooth formation give slightly younger ages than those based on emergence." (Walker & Leakey, 1993, p. 207)
- KNM-WT 15000: Kenya National Museum; West Turkana; item 15000
- Graves RR, Lupo AC, McCarthy RC, Wescott DJ, Cunningham DL (2010). "Just how strapping was KNM-WT 15000?". J Hum Evol 59 (5): 542–554. doi:10.1016/j.jhevol.2010.06.007. PMID 20846707.
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- http://www.pbs.org/wgbh/nova/beta/evolution/becoming-human-part-2.html, at 38:00 minutes on countdown
- Lewin, p. 164
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