Vermeij Geerat J
Department of Geology, University of California, One Shields Avenue, Davis, CA 95616, USA.
Proc Natl Acad Sci U S A. 2006 Feb 7;103(6):1804-9. doi: 10.1073/pnas.0508724103. Epub 2006 Jan 27.
Many events in the history of life are thought to be singular, that is, without parallels, analogs, or homologs in time and space. These claims imply that history is profoundly contingent in that independent origins of life in the universe will spawn radically different histories. If, however, most innovations arose more than once on Earth, histories would be predictable and replicable at the scale of functional roles and directions of adaptive change. Times of origin of 23 purportedly unique evolutionary innovations are significantly more ancient than the times of first instantiation of 55 innovations that evolved more than once, implying that the early phases of life's history were less replicable than later phases or that the appearance of singularity results from information loss through time. Indirect support for information loss comes from the distribution of sizes of clades in which the same minor, geologically recent innovation has arisen multiple times. For three repeated molluscan innovations, 28-71% of instantiations are represented by clades of five or fewer species. Such small clades would be undetectable in the early history of life. Purportedly unique innovations either arose from the union and integration of previously independent components or belong to classes of functionally similar innovations. Claims of singularity are therefore not well supported by the available evidence. Details of initial conditions, evolutionary pathways, phenotypes, and timing are contingent, but important ecological, functional, and directional aspects of the history of life are replicable and predictable.
生命史上的许多事件被认为是独一无二的，也就是说，在时间和空间上没有相似、类似或同源的事件。这些说法意味着历史具有极大的偶然性，因为宇宙中生命的独立起源将产生截然不同的历史。然而，如果大多数创新在地球上不止一次出现，那么历史在功能作用和适应性变化方向的规模上将是可预测和可复制的。据称23项独特进化创新的起源时间明显早于55项多次进化的创新首次出现的时间，这意味着生命历史的早期阶段比后期阶段更不可复制，或者独特性的出现是由于信息随时间的丢失。信息丢失的间接证据来自于同一微小的、地质上近期的创新多次出现的进化枝大小分布。对于三项重复出现的软体动物创新，28% - 71%的实例由五个或更少物种的进化枝代表。这样小的进化枝在生命的早期历史中是无法检测到的。据称独特的创新要么源于先前独立组件的结合与整合，要么属于功能相似的创新类别。因此，独特性的说法没有得到现有证据的充分支持。初始条件、进化途径、表型和时间的细节是偶然的，但生命历史中重要的生态、功能和方向方面是可复制和可预测的。
