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

化石足骨很少发现与可识别的骨骼有关，而且往往是零碎的；当我们发现我们的远古祖先的部分脚时，它通常会被严重咀嚼。此外，这些化石很少给出我们早期祖先行走方式的明确迹象，因为它们穿过一系列嵌套的复杂软组织，从韧带到皮肤，因此骨骼只能与我们行走的地面远程互动。另一方面，当我们的远古祖先走过松软的土地时留下的脚印和轨道是我们最接近于“僵化行为”的地方，因为它们是我们对地面施加的力量的直接记录，以平衡我们自己和推动我们的行走。因此，它们可能是人类行走进化的极好证据。然而，直到最近，我们还缺乏工具来释放它们的科学潜力。例如，大约375万年前由露西和她的亲戚们制作的著名的Laetoli脚印的功能意义已经争论了30多年，一位科学家根据个别脚印的特征与另一位科学家相矛盾--在一个案例中，他们把走过人类祖先脚印的野兔的脚印误认为是它的大脚趾的脚印。我们需要一些方法来告诉我们化石轨道的共同特征是什么；识别它们的“中心趋势”，以便我们能够消除偏见。这并不容易，因为脚印是由软组织形成的，没有容易识别的地标点。参与这个项目的两个小组中的一个研究行走的机制，使用计算机模拟技术，并进行一些“横向思维”，发现用于分析大脑中化学模式分布的方法是比较脚印的理想方法。另一个小组是寻找和挖掘化石足迹的专家，他们最近在肯尼亚发现了一组令人兴奋的新指纹，大约是Laetoli指纹的一半，由我们自己所属的第一批成员制造：人。他们使用先进的激光扫描技术以三维细节记录指纹，就像他们以前在Laetoli所做的那样。很可能在接下来的三年里，他们会发现更多新的足迹。人类行走就像一个节拍器，当身体在接触地面的脚上向前摆动时，节省了能量，然后可以用来为下一步提供动力。但由于我们又高又瘦的体型，我们的走路从一边到另一边都不稳定，我们的臀部肌肉需要工作，以对抗当一条腿接管另一条腿的支撑时，我们侧翻的倾向。像企鹅这样矮小的蹲式动物从一边到另一边更稳定，而且实际上可以通过它们的摇摇晃晃的步态来横向节省摆的能量。像露西这样的远古人类祖先也有类似的下蹲和稳定的体型--他们是否也以同样的方式节省能源？拉托利的足迹很可能包含了答案。将它们与早期人类的新脚印进行比较，应该会告诉我们很多关于露西是如何将灵活的脚变成更坚硬的脚的，这种脚可以用力推出，让我们几乎毫不费力地走或跑很长的距离。要做到这一点，我们不仅需要制作复杂的行走和足迹形成的计算机模型，这可以重建这些早期人类祖先的平衡和节能机制，并将它们与脚力和足迹形式联系起来，还需要在软泥和火山灰中进行物理实验，这将把这些模型与现实世界联系起来。但我们也必须寻找更多的足迹，这可以填补我们正在研究的变化的一些细节。因此，通过合作，我们拥有了技能、工具和证据来解释在关键时期行走的进化，即早期可能在树上呆了一段时间的两足动物和大步走远的人之间的过渡。

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.