This week we enter the final stages of our journey, moving from the transitional hominins safely into the early members of our own genus Homo. Again, some controversy exists over whether to split the earliest accepted members of our genus into Homo ergaster in Africa and H. erectus in Asia, or whether to lump them both into H. erectus. Personally, I prefer lumping to splitting in this case – H. erectus it is.
Fig. 1 shows the amazing skeleton first unearthed in 1984 by a team led by Richard Leakey near Nariokotome on the western shores of Lake Turkana, Kenya. The skeleton is typical of the species H. erectus (upright man) which was present in Africa (and Asia for the first time!) from 1.9 million years ago (Mya) and even as recently as 54 000 years ago (0.054 Mya) according to some estimates of skeletons from Java (Swisher III et al., 1996). Turkana Boy himself lived 1.6 Mya and is thought to have been around 9 years old at death, although physically more like a modern 12-15 year-old because H. erectus developed more quickly. He would probably have been 6′ tall at adulthood and the skeleton demonstrates that he had fully modern limb proportions indicating efficient bipedalism, modern curvature of the spine, a modern pelvis in terms of relative height and width with flared iliac blades, a bicondylar angle of the femur and an ankle articulation with the tibia which was perpendicular to the long axis of the tibia.
Fig. 2 shows the foot of H. erectus from Dmanisi, Georgia on the right.
Although it’s a lot smaller, the composite Dmanisi foot has a big toe that is almost completely in line with the other toes (adducted) and the size of the talus at the bottom of the photo demonstrates that H. erectus was a habitual biped at least and maybe even an obligate biped. As was the case with Au. afarensis, the golden standard for proving bipedalism comes from direct evidence of a hominin walking upright. Fossilised footprints in sediment laid down in Ileret, Kenya 1.5 Mya (fig. 3) show evidence of an arched sole both on the lateral side and the medial side of the foot providing a very rigid lever for weight transfer.
Laser analysis of the depth of each print also shows that weight transfer also passed from the lateral side to the medial side of the foot just as in modern humans, as shown in fig. 4
Together, these fossils demonstrate that H. erectus walked just like us and likely spent very little, if any, time in the trees. However the Dmanisi specimen shows that the fifth metatarsal (the long bone leading to the little toe) of H. erectus was the least robust, whereas it is the second most robust metatarsal in modern humans. This finding suggests that something was missing from the early Homo locomotor repertoire – that something was very likely running (Raichlen et al., 2011). More next week!
Bennett, M. R., Harris, J. W. K., Richmond, B. G., Braun, D. R., Mbua, E., Kiura, P., … Gonzalez, S. (2009). Early hominin foot morphology based on 1.5-million-year-old footprints from Ileret, Kenya. Science (New York, N.Y.), 323, 1197–201. doi:10.1126/science.1168132
Foley J, 2002, 2011. Fossil hominids – the evidence for human evolution: KNM-WT 15000. The Talk Origins Archive. Available from: http://www.talkorigins.org/faqs/homs/index.html. Accessed: 27/05/14.
Harcourt-Smith, W. (2002). Form and function in the hominoid tarsal skeleton. University College London.
Pontzer, H., Rolian, C., Rightmire, G. P., Jashashvili, T., Ponce de León, M. S., Lordkipanidze, D., & Zollikofer, C. P. E. (2010). Locomotor anatomy and biomechanics of the Dmanisi hominins. Journal of Human Evolution, 58(6), 492–504. doi:10.1016/j.jhevol.2010.03.006
Raichlen, D. a, Armstrong, H., & Lieberman, D. E. (2011). Calcaneus length determines running economy: implications for endurance running performance in modern humans and Neandertals. Journal of Human Evolution, 60(3), 299–308. doi:10.1016/j.jhevol.2010.11.002
Swisher, C. C., Rink, W. J., Antón, S. C., Schwarcz, H. P., Curtis, G. H., & Widiasmoro, A. S. (1996). Latest Homo erectus of Java: Potential Contemporaneity with Homo sapiens in Southeast Asia. Science , 274 (5294 ), 1870–1874. doi:10.1126/science.274.5294.1870.