Manley G A
Institut für Zoologie, Technische Universität München, Lichtenbergstr. 4, 85747 Garching, Germany.
Proc Natl Acad Sci U S A. 2000 Oct 24;97(22):11736-43. doi: 10.1073/pnas.97.22.11736.
The hearing organ of the inner ear was the last of the paired sense organs of amniotes to undergo formative evolution. As a mechanical sensory organ, the inner-ear hearing organ's function depends highly on its physical structure. Comparative studies suggest that the hearing organ of the earliest amniote vertebrates was small and simple, but possessed hair cells with a cochlear amplifier mechanism, electrical frequency tuning, and incipient micromechanical tuning. The separation of the different groups of amniotes from the stem reptiles occurred relatively early, with the ancestors of the mammals branching off first, approximately 320 million years ago. The evolution of the hearing organ in the three major lines of the descendents of the stem reptiles (e.g., mammals, birds-crocodiles, and lizards-snakes) thus occurred independently over long periods of time. Dramatic and parallel improvements in the middle ear initiated papillar elongation in all lineages, accompanied by increased numbers of sensory cells with enhanced micromechanical tuning and group-specific hair-cell specializations that resulted in unique morphological configurations. This review aims not only to compare structure and function across classification boundaries (the comparative approach), but also to assess how and to what extent fundamental mechanisms were influenced by selection pressures in times past (the phylogenetic viewpoint).
内耳的听觉器官是羊膜动物成对感觉器官中最后一个经历形态进化的。作为一个机械感觉器官，内耳听觉器官的功能高度依赖于其物理结构。比较研究表明，最早的羊膜动物脊椎动物的听觉器官小而简单，但拥有具有耳蜗放大机制、电频率调谐和初始微机械调谐的毛细胞。不同的羊膜动物类群与主干爬行动物的分离发生得相对较早，哺乳动物的祖先首先分支出来，大约在3.2亿年前。因此，主干爬行动物后代的三大类群（如哺乳动物、鸟类 - 鳄鱼和蜥蜴 - 蛇）的听觉器官进化在很长一段时间内是独立发生的。中耳的显著且平行的改进在所有谱系中引发了乳头伸长，同时伴随着感觉细胞数量的增加，微机械调谐增强以及特定类群的毛细胞特化，从而导致了独特的形态结构。本综述不仅旨在跨越分类界限比较结构和功能（比较方法），还旨在评估过去的选择压力如何以及在多大程度上影响了基本机制（系统发育观点）。
