de Queiroz Alan
Department of Environmental, Population, and Organismic Biology and Natural History Museum, University of Colorado, Boulder 80309-0334, USA.
Syst Biol. 2002 Dec;51(6):917-29.
Key innovations have often been invoked to explain the exceptional diversification of particular groups. However, there are few convincing examples of traits that are repeatedly and consistently associated with increased diversification. The paucity of such cases may reflect the contingent nature of the diversifying effect of key traits. These contingencies can be viewed as statistical interactions between the trait and at least three kinds of factors: (1) other taxa, (2) other traits of the group itself, and (3) the physical environment. I describe tentative examples in each of these categories: (1) a dampening of the diversification of clades with image-forming eyes by groups that earlier evolved such eyes, (2) an effect of growth form (woody or herbaceous) on the diversifying effect of biotic seed dispersal in angiosperms, and (3) an effect of atmospheric CO(2) level on the diversifying effect of C(4) photosynthesis in monocots. These examples suggest the need for more complex analyses of the relationship between possible key traits and diversification. They also suggest that radiations may be predictable given certain circumstances, thus supporting a view of evolution as both predictable and contingent. Ironically, a certain degree of predictability may be critical to arguments for evolutionary contingency.
关键创新常常被用来解释特定类群的异常多样化。然而，很少有令人信服的例子表明某些性状会反复且持续地与多样化增加相关联。此类情况的匮乏可能反映了关键性状多样化效应的偶然性。这些偶然性可被视为该性状与至少三种因素之间的统计相互作用：（1）其他分类群，（2）该类群自身的其他性状，以及（3）物理环境。我描述了这几类中的一些初步例子：（1）早期进化出成像眼睛的类群对具有成像眼睛的分支多样化的抑制作用，（2）生长形式（木本或草本）对被子植物中生物种子传播多样化效应的影响，以及（3）大气二氧化碳水平对单子叶植物中C4光合作用多样化效应的影响。这些例子表明需要对可能的关键性状与多样化之间的关系进行更复杂的分析。它们还表明在某些情况下辐射可能是可预测的，从而支持了进化既是可预测的又是偶然的这一观点。具有讽刺意味的是，一定程度的可预测性对于进化偶然性的论证可能至关重要。
