The Evolution of Diagonal-sequence Gaits in Primates: A New Approach to the Problem

当行走时，大多数四足动物通常在同一侧的后足之后放下每个前足（也就是说，右后足后跟右前足，等等）。 四足灵长类动物（狐猴、猴子、猿等）在每一个后脚落地之后，前脚从对侧向下的情况下是不典型的（也就是说，右后脚落地之后是左前脚落地，等等）。 虽然灵长类动物的这些所谓的对角序列（DS）步态有很好的文献记载，但它们的功能意义已经困扰了生物学家超过世纪。 初步数据显示，DS步态也是树栖有袋类动物的特征，它们与灵长类动物相似，都是树居动物，后足抓握。 DS步态允许所有这些动物用一个延长的后脚支撑自己，放在身体质心下的一个经过验证的支撑上，然后把前脚放在一个可能不稳定的支撑上。 理论上的考虑意味着相位关系前肢和后肢的运动循环之间的对角性（“对角线”）应随后肢相对于前肢的占空因数直接变化，该对角性应随支撑斜率直接变化而随支撑直径相反地变化，占空比与对角线的相关性经历了从负相关到负相关的历史性转变（如在典型的哺乳动物中）到阳性（如在高等灵长类动物中）。 高速摄像机将被用来记录足迹序列的四个支持类型的一套15个物种选择控制的相关变量。 收集的数据将用于测试从理论中得出的经验预测。 这些结果有望为有关灵长类起源和人类谱系早期阶段的争议提供新的线索。

When walking, most quadrupeds typically put down each forefoot just after the hindfoot on the same side (that is, the right hind footfall is followed by the right fore footfall, and so on). Quadrupedal primates (lemurs, monkeys, apes, etc.) are atypical in placing down the forefoot from the opposite side just after each hind footfall (that is, the right hind footfall is followed by the left fore footfall, and so on). Although these so-called diagonal-sequence (DS) gaits of primates are well documented, their functional significance has eluded biologists for over a century. Preliminary data show that DS gaits are also characteristic of arboreal marsupials, which resemble primates in being tree-dwelling animals with grasping hind feet. DS gaits allow all these animals to support themselves with a protracted hind foot, placed on a proven support under the body's center of mass, before putting down a forefoot on a potentially precarious support. Theoretical considerations imply that the phase relationship ("diagonality") between the movement cycles of the fore and hind limbs should vary directly with the duty factor of the hindlimb relative to that of the forelimb, that diagonality should vary directly with support slope and inversely with support diameter, and that the correlation between duty factor and diagonality has undergone a historical transformation from negative (as in typical mammals) to positive (as in higher primates). High-speed camcorders will be used to record footfall sequences on four support types for a suite of 15 species selected to control for the relevant variables. The data collected will be used to test the empirical predictions derived from the theory. The results are expected to shed new light on controversies concerning primate origins and the early stages of the human lineage.