Digital Conservation and Reconstruction of 'Fossilized Behaviour': the evolution of the human foot as revealed by ancient footprint trails

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Fossil footbones are rarely found associated with identifiable skeletons, and are often fragmentary; and when we do find a partial foot of one of our ancient ancestors it has usually been badly chewed. In addition such fossil rarely give definite indications of the way our early ancestors walked, as they act through a nested series of complicated soft tissues, from ligaments, out to the skin, and therefore the bones interact only remotely with the ground on which we walk. On the other hand, the footprints and trackways which were left when our distant ancestors walked across soft ground are the closest we can come to 'fossilized behaviour', as they are direct records of the forces we apply to the ground to balance ourselves and propel our walking. They are therefore potentially excellent evidence of the evolution of human walking. However, until recently we have lacked the tools with which to unlock their scientific potential. For example, the functional significance of the famous Laetoli footprints made some 3.75 million years ago by 'Lucy' and her relatives has been argued about for over 30 years, one scientist contradicting another, on the basis of features of individual prints - and in one case mistaking the footprint of a hare which walked across the human ancestor's footprints as the print of its big toe. We need methods which will tell us what are the common features of fossil trackways; identifying their 'central tendency' so that we can eliminate bias. This isn't easy, since footprints, being made by soft tissue, have no easily recognisable landmark points. One of the two groups involved in this project work on the mechanics of walking, using computer-simulation techniques, and engaging in some 'lateral thinking', found that methods used to analyze the distribution of chemical patterns in the brain are ideal for comparing footprints. The other group are specialists in finding and excavating fossil footprints, and recently discovered an exciting new set of prints in Kenya, about half the age of the Laetoli prints and made by the first members of our own 'genus': Homo. They used advanced laser-scanning techniques to record the prints in three-dimensional detail, as they had previously done for those at Laetoli. It's very likely that in the next three years they will find even more new footprint trails. Human walking works like a metronome, saving energy as the body swings forward over the foot which contacts the ground, which can then be used to power the next stride. But because of our tall, thin build, our walking is unstable from side to side, and our hip muscles need to work to counter our tendency to fall over sideways when one leg takes over support from the other. Short, squatter animals like penguins are more stable from side to side, and can actually save pendulum-energy sideways on, by their 'waddling' gait. Distant human ancestors like Lucy had a similar squat and stable build - did they save energy the same way? It is likely that the footprints at Laetoli may contain the answer. Comparing them with the new footprints of early Homo should tell us a lot about how Lucy's flexible foot changed into a stiffer one which could push-off hard enough to let us walk or run long distances nearly effortlessly. To do so, we need not only to make sophisticated computer models of walking and footprint formation, which can recreate balance and energy-saving mechanisms in these early human ancestors, and relate them to foot forces and footprint form, but to do physical experiments in soft mud and ash which will tie these models into the real world. But we must also look for more footprints, which can fill in some of the details of the changes we are studying. Thus, working together, we have the skills, tools and evidence to interpret the evolution of walking at a crucial time period, the transition between an early biped that probably spent some time in the trees, and a striding long-distance walker.