Center for the Study of Human Origins, Department of Anthropology, New York University, NY 10003, USA.
Am J Phys Anthropol. 2012 May;148(1):111-22. doi: 10.1002/ajpa.22049. Epub 2012 Mar 15.
A fundamental adaptation to orthograde posture and locomotion amongst living hominoid primates is a numerically reduced lumbar column, which acts to stiffen the lower back and reduce injuries to the intervertebral discs. A related and functionally complementary strategy of spinal stability is a caudal position of the diaphragmatic vertebra relative to the primitive condition found in nonhominoid primates and most other mammals. The diaphragmatic vertebra marks the transition in vertebral articular facet (zygapophysis) orientation, which either resists (prediaphragmatic) or allows (postdiaphragmatic) trunk movement in the sagittal plane (i.e., flexion and extension). Unlike most mammals, which have dorsomobile spines (long lumbar columns and cranially placed diaphragmatic vertebrae) for running and leaping, hominoids possess dorsostable spines (short lumbar columns and caudally placed diaphragmatic vertebrae) adapted to orthogrady and antipronogrady. In contrast to humans and other extant hominoids, all known early hominin partial vertebral columns demonstrate cranial displacement of the diaphragmatic vertebra. To address this difference, variation in diaphragmatic placement is assessed in a large sample of catarrhine primates. I show that while hominoids are characterized by modal common placement of diaphragmatic and last rib-bearing vertebrae in general, interspecific differences in intraspecific patterns of variation exist. In particular, humans and chimpanzees show nearly identical patterns of diaphragmatic placement. A scenario of hominin evolution is proposed in which early hominins evolved cranial displacement from the ancestral hominid condition of common placement to achieve effective lumbar lordosis during the evolution of bipedal locomotion.
在现生灵长类动物中，直立姿势和运动的基本适应是腰椎数量减少，这有助于使下背部更坚固，并减少椎间盘损伤。脊柱稳定性的另一个相关且功能互补的策略是膈椎的尾部位置，相对于非灵长类动物和大多数其他哺乳动物的原始位置。膈椎标志着椎关节突（关节突）方向的转变，这种转变要么抵抗（前膈），要么允许（后膈）躯干在矢状面（即屈伸）运动。与大多数具有背侧活动脊柱（长腰椎和头部位置的膈椎）用于奔跑和跳跃的哺乳动物不同，人科动物具有背侧稳定的脊柱（短腰椎和尾部位置的膈椎），适应于直立和前向倾斜。与人类和其他现存人科动物不同，所有已知的早期人科动物部分脊柱都显示膈椎向头部移位。为了解决这个差异，对大量的大型猫科灵长类动物的膈椎位置进行了评估。我表明，虽然人科动物通常以膈椎和最后肋骨承载椎骨的模式共同位置为特征，但在种内模式的变异中存在种间差异。特别是，人类和黑猩猩显示出几乎相同的膈椎位置模式。提出了一种人科动物进化的情景，即在双足运动进化过程中，早期人科动物从共同位置的祖先人科动物状态进化出头部移位，以实现有效的腰椎前凸。
