Pagel M D, Harvey P H
Department of Zoology, University of Oxford, U. K.
Q Rev Biol. 1988 Dec;63(4):413-40. doi: 10.1086/416027.
Comparative methods can be used to test ideas about adaptation by identifying cases of either parallel or convergent evolutionary change across taxa. Phylogenetic relationships must be known or inferred if comparative methods are to separate the cross-taxonomic covariation among traits associated with evolutionary change from that attributable to common ancestry. Only the former can be used to test ideas linking convergent or parallel evolutionary change to some aspect of the environment. The comparative methods that are currently available differ in how they manage the effects brought about by phylogenetic relationships. One method is applicable only to discrete data, and uses cladistic techniques to identify evolutionary events that depart from phylogenetic trends. Techniques for continuous variables attempt to control for phylogenetic effects in a variety of ways. One method examines the taxonomic distribution of variance to identify the taxa within which character variation is small. The method assumes that taxa with small amounts of variation are those in which little evolutionary change has occurred, and thus variation is unlikely to be independent of ancestral trends. Analyses are then concentrated among taxa that show more variation, on the assumption that greater evolutionary change in the character has taken place. Several methods estimate directly the extent to which ancestry can predict the observed variation of a character, and subtract the ancestral effect to reveal variation of phylogeny. Yet another can remove phylogenetic effects if the true phylogeny is known. One class of comparative methods controls for phylogenetic effects by searching for comparative trends within rather than across taxa. With current knowledge of phylogenies, there is a trade-off in the choice of a comparative method: those that control phylogenetic effects with greater certainty are either less applicable to real data, or they make restrictive or untestable assumptions. Those that rely on statistical patterns to infer phylogenetic effects may not control phylogeny as efficiently but are more readily applied to existing data sets.
比较方法可用于通过识别不同分类群间平行或趋同进化变化的案例来检验关于适应性的观点。如果要将与进化变化相关的性状间的跨分类群共变与归因于共同祖先的共变区分开来，就必须知道或推断系统发育关系。只有前者可用于检验将趋同或平行进化变化与环境的某些方面联系起来的观点。目前可用的比较方法在处理系统发育关系所带来的影响方面各不相同。一种方法仅适用于离散数据，并使用分支分类技术来识别偏离系统发育趋势的进化事件。针对连续变量的技术试图以各种方式控制系统发育效应。一种方法是检查方差的分类分布，以识别性状变异较小的分类群。该方法假定变异量小的分类群是那些发生进化变化很少的分类群，因此变异不太可能独立于祖先趋势。然后将分析集中在显示出更多变异的分类群中，假定该性状发生了更大程度的进化变化。几种方法直接估计祖先能够预测一个性状观察到的变异程度，并减去祖先效应以揭示系统发育的变异。如果知道真实的系统发育关系，则还有另一种方法可以消除系统发育效应。一类比较方法通过在分类群内部而不是跨分类群搜索比较趋势来控制系统发育效应。基于目前对系统发育的了解，在选择比较方法时存在权衡：那些能更确定地控制系统发育效应的方法要么不太适用于实际数据，要么做出了限制性或不可检验的假设。那些依靠统计模式来推断系统发育效应的方法可能无法同样有效地控制系统发育，但更易于应用于现有数据集。
