A biface, Acheulean hand axe is more than object of beauty produced by exquisite skill, this industrial genre was invented by African Homo ergaster around 1.6 Ma ago, became a central feature of Palaeolithic archaeology, and lasted until the last few hundred thousand years. Nobody doubts that production of these objects implies a brain that fashioned able to visualise a complex shape within a shapeless lump of rock and to devise a way of achieving it. Moreover, its longevity spanning several species of Homo to our own shows that skills were efficiently passed down through hundreds of thousand generations: possible evidence for linguistic skills in the makers and teachers. But what was it for? Experts have been at a loss to agree on a function: too heavy for hafting to a spear; more awkward for cutting than earlier Oldowan pebble fragments; produced with careful three-dimensional symmetry when a hand tool needs none; time consuming to make yet often found in great abundance and apparently hardly used. One idea is that they were in fact for throwing, in the manner of a discus, yet broken biface axes are rare. A more appealing hypothesis is that they were made for ‘show’ as an element in human sexual selection (Kohn, M. & Mithen, S. 1999. Hand axes: products of sexual selection? Antiquity, v. 73, p. 518-526). Kohn and Mithen argued that the primary function of hand axes was to advertise a maker’s “good genes”: an indicator of the knapper’s geographic knowledge of suitable resources; his ability to execute a plan; his dexterity and patience; and his social awareness. Those are all attractive qualities in a potential mate. They also suggested that the axes’ often near-pristine quality and occurrence in great numbers at some sites indicate that once their purpose was served, they were thrown away: ‘That man is so cool, he must be good at surviving’. Ten years after Kohn and Mithen first mooted the hypothesis it has come under criticism by April Nowell and Melanie Lee Chang, of the universities of Victoria, Canada and Oregon USA, respectively (Nowell, A. & Chang M.L. 2009.The case against sexual selection as an explanation of handaxe morphology. Paleoanthropology, v. 2009, p. 77-88).
The critique begins by examining Kohn and Mithen’s interest in symmetry as an element in attractiveness, that Nowell and Chang concede, but consider to have arisen not in a sexual context but in development of vision, despite vision being an evolutionary ‘given’ vastly older than hominins. After a discussion of how fully modern human females base their sexual choices on non-physical attributes of potential mates, such as “niceness,” intelligence, sense of humour, compatibility, willingness to work hard and evidence that the partner in question is attracted to them, Nowell and Chang examine available archaeological evidence. Much of this concerns the ‘absence of evidence’. For instance, there is no evidence to suggest that females did not make hand axes and living females in gatherer-hunter societies do make tools. Other criticisms include: the absence of hand axes from Asia until migration there by H. sapiens [but the biface axe had not been invented when H. ergaster migrated there from Africa around 1.8 Ma]; not all biface axes are symmetrical [but they are nonetheless impressive]; and axes in large numbers generally occur where prey has been butchered, as at Boxgrove, and may have accumulated by hundreds of years of use and loss at such sites by seasonal hunting. The most serious criticism is that some hand axes do show minute patterns that indicate that they were used; although most axes have never been examined for wear patterns. My own conclusion is that the critique is based on absence of evidence for biface axes as ritual objects in sexual selection, but that is not evidence of absence, and I wonder if the 10 years taken to bring together contrary evidence has a bit to do with casting doubt on a not quite ‘PC’ idea. There are many intriguing facets of the fossil and archaeological records of hominins, none more so than those which may have a cultural connotation, like ochre caches (see Deeper roots of culture in EPN of March 2009) and the tear-shaped Acheulean axe. For most we may never know their true context, but can be sure that any curiosity and imagination we apply are reflections of imaginative and curious forebears.
Homo erectus in a cold climate
The famous Zhoukoudian Cave where Peking Man, now known to have been Homo erectus, was first found in 1929 is a lugubrious place. It seems the hominin fossil remains of at least 40 individuals were dragged there and eaten, hopefully by predators. They are by no means the oldest Asian hominins at less than 1 Ma, and their ancestors, probably African H. ergaster, migrated that far around 1.6 to 1.8 Ma ago. Until this year, decent ages from Zhoukoudian were a problem: the errors on estimates of around 500 ka were too large (the likely time lies in a ‘datability gap’ between the capabilities of Ar-Ar and 14C dating methods) to see if the hominins were living at such a high latitude (40ºN) in warm or cold conditions. The latter would be of great interest as it suggests both the use of fire and clothing, and probably adaptation to cooked tubers. In fact, even in the current interglacial episode Beijing gets mighty cold in winter. However, cosmic-ray bombardment can produce unstable isotopes that are suited to dating in that gap, provided materials have been exposed to them. The fossil-containing sediments in Zhoukoudian Cave contain quartz that was exposed at the surface and washed in at the same time as H. erectus individuals were dragged in. Decay of cosmogenic 26Al to 10Be and measurement of parent and daughter isotopes in quartz grains have yielded ages of 770±80 ka, somewhat older than earlier estimates (Shen, G. et al. 2009. Age of Zhoukoudian Homo erectus determined with 26Al/10Be dating. Nature, v. 458, p. 198-200). This age roughly correlates with layers in the western Chinese windblown loess deposits that were deposited during the dry conditions of a minor glacial episode.
See also: Ciochon, R.L. & Bettis, E.A. 2009. Asian Homo erectus converges in time. Nature, v. 458, p.153-154. Gibbo0ns, A. 2009. Ice age no barrier to ‘Peking Man’. Science, v. 323, p. 1419.
Walking with the ancestors
From time to time the most evocative hominin trace fossils come to light, such as the Australopithecus afarensis footprints fount by Mary Leakey at Laetoli in Tanzania. A recent one is of footprints of a probable H. ergaster dating back to 1.5 Ma near Lake Turkana in Kenya, not far from the site of the famous ‘Turkana Boy’ skeleton of the same species (Bennett, M.R. and 11 others 2009. Early hominin foot morphology based on 1.5-million-year old footprints from Ileret, Kenya. Science, v. 323, p. 1197-1201). Not only does the trackway reveal details of flesh, skin and bones of the feet, but careful analysis of 3-D scans of the prints, in the context of the mechanical properties of the material walked upon, allows the authors to show that the person who left them moved in essentially the same way as do we when walking through soft mud. They are distinctly different from the Laetoli prints, showing arches and very distinct big toes that are so necessary for ‘springiness’ and bipedal balance respectively.
See also: Crompton, R.W. & Pataky, T.C. 2009. Stepping out. Science, v. 323, p. 1174-1175.