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

化石脚骨很少与可识别的骨骼联系在一起，而且往往是支离破碎的;当我们发现我们古代祖先的一只脚时，它通常被严重咀嚼。此外，这些化石很少能明确指出我们早期祖先的行走方式，因为他们通过一系列嵌套的复杂软组织，从韧带到皮肤，因此骨骼与我们行走的地面只有很小的互动。另一方面，当我们遥远的祖先走过柔软的地面时留下的脚印和轨道是我们最接近“行为化”的，因为它们是我们施加在地面上的力量的直接记录，以平衡我们自己并推动我们的行走。因此，它们可能是人类行走进化的绝佳证据。然而，直到最近，我们还缺乏释放其科学潜力的工具。例如，375万年前由“露西”和她的亲戚们留下的著名的莱托利脚印的功能意义已经争论了30多年，一个科学家反驳另一个科学家，根据个人脚印的特征-在一个案例中，误将走过人类祖先脚印的野兔脚印误认为是大脚趾的脚印。我们需要的方法将告诉我们什么是化石轨道的共同特征;确定他们的“集中趋势”，以便我们可以消除偏见。这并不容易，因为脚印是由软组织形成的，没有容易识别的标志点。参与该项目的两个小组中的一个研究行走力学，使用计算机模拟技术，并从事一些“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足迹的理想方法。另一组是寻找和挖掘化石足迹的专家，最近在肯尼亚发现了一组令人兴奋的新脚印，大约是Laetoli脚印年龄的一半，由我们自己的“属”的第一批成员制作：人属。他们使用先进的激光扫描技术以三维细节记录指纹，就像他们以前在莱托利所做的那样。很可能在未来三年内，他们会发现更多新的足迹。人类走路就像节拍器一样，当身体向前摆动时，脚接触地面，从而节省能量，然后可以用来为下一步提供动力。但是由于我们又高又瘦的身材，我们的行走从一边到另一边是不稳定的，当一条腿从另一条腿接管支撑时，我们的臀部肌肉需要工作来对抗我们侧身摔倒的倾向。像企鹅这样的矮个子动物从一边到另一边更稳定，实际上可以通过他们的“摇摆”步态节省侧向能量。像露西这样遥远的人类祖先也有类似的蹲下和稳定的体型--他们也是这样节省能量的吗？拉托里的脚印可能包含答案。将它们与早期人属的新足迹进行比较，应该可以告诉我们很多关于露西的灵活的脚是如何变成一个更坚硬的脚的，它可以用力地推动，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，这可以在这些早期人类祖先身上重现平衡和节能机制，并将它们与脚力和足迹形式联系起来，而且还需要在软泥和灰烬中进行物理实验，将这些模型与真实的世界联系起来。但我们也必须寻找更多的足迹，这些足迹可以填补我们正在研究的变化的一些细节。因此，通过共同努力，我们拥有了在一个关键时期解释行走进化的技能、工具和证据，即从可能在树上呆了一段时间的早期步行者到大步长距离步行者的转变。

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.