Frelat Mélanie A, Shaw Colin N, Sukhdeo Simone, Hublin Jean-Jacques, Benazzi Stefano, Ryan Timothy M
Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg, South Africa; Department of Cultural Heritage, University of Bologna, Ravenna, Italy; UMR 7268 ADES, Aix-Marseille Université/EFS/CNRS, Marseille, France.
PAVE Research Group, Department of Archaeology & Anthropology, University of Cambridge, Cambridge, UK; McDonald Institute for Archaeological Research, Department of Archaeology & Anthropology, University of Cambridge, Cambridge, UK; Cambridge BioTomography Centre, Department of Zoology, University of Cambridge, Cambridge, UK.
J Hum Evol. 2017 Jul;108:147-160. doi: 10.1016/j.jhevol.2017.03.006. Epub 2017 May 22.
The dispersal of the genus Homo out of Africa approximately 1.8 million years ago (Ma) has been understood within the context of changes in diet, behavior, and bipedal locomotor efficiency. While various morphological characteristics of the knee and ankle joints are considered part of a suite of traits indicative of, and functionally related to, habitual bipedal walking, the timing and phylogenetic details of these morphological changes remain unclear. To evaluate the timing of knee and ankle joint evolution, we apply geometric morphometric methods to three-dimensional digital models of the proximal and distal tibiae of fossil hominins, Holocene Homo sapiens, and extant great apes. Two sets of landmarks and curve semilandmarks were defined on each specimen. Because some fossils were incomplete, digital reconstructions were carried out independently to estimate missing landmarks and semilandmarks. Group shape variation was evaluated through shape-and form-space principal component analysis and fossil specimens were projected to assess variation in the morphological space computed from the extant comparative sample. We show that a derived proximal tibia (knee) similar to that seen in living H. sapiens evolved with early Homo at ∼2 Ma. In contrast, derived characteristics in the distal tibia appear later, probably with the arrival of Homo erectus. These results suggest a dissociation of the morphologies of the proximal and distal tibia, perhaps indicative of divergent functional demands and, consequently, selective pressures at these joints. It appears that longer distance dispersals that delivered the Dmanisi hominins to Georgia by 1.8 Ma and H. erectus to east-southeast Asia by 1.6 Ma were facilitated by the evolution of a morphologically derived knee complex comparable to that of recent humans and an ankle that was morphologically primitive. This research sets the foundation for additional paleontological, developmental, and functional research to better understand the mechanisms underlying the evolution of bipedalism.
约180万年前，人属从非洲扩散开来，这一过程是在饮食、行为和双足运动效率变化的背景下被理解的。虽然膝关节和踝关节的各种形态特征被认为是一系列与习惯性双足行走相关且具有指示作用的性状的一部分，但这些形态变化的时间和系统发育细节仍不清楚。为了评估膝关节和踝关节进化的时间，我们将几何形态测量方法应用于化石人类、全新世智人和现存大猩猩近端和远端胫骨的三维数字模型。在每个标本上定义了两组地标点和曲线半地标点。由于一些化石不完整，独立进行了数字重建以估计缺失的地标点和半地标点。通过形状和形态空间主成分分析评估群体形状变异，并对化石标本进行投影，以评估从现存比较样本计算出的形态空间中的变异。我们发现，与现存智人相似的衍生近端胫骨（膝盖）在约200万年前随着早期人类的出现而进化。相比之下，远端胫骨的衍生特征出现得较晚，可能与直立人的出现有关。这些结果表明近端和远端胫骨形态的分离，这可能表明这些关节存在不同的功能需求以及相应的选择压力。看来，形态上衍生的类似现代人的膝关节复合体和形态上原始的踝关节的进化，促进了将德马尼西人在180万年前送到格鲁吉亚以及将直立人在160万年前送到东亚东南部的更长距离扩散。这项研究为进一步的古生物学、发育学和功能研究奠定了基础，以更好地理解双足行走进化背后的机制。
