In a recent commentary in this journal Seifert et al. (2016) propose returning to a school of classification largely abandoned by systematists, in which both monophyletic and paraphyletic groups are formally recognized. This approach, dubbed ‘‘evolutionary classification’’, has proved to be unattractive and impractical because the basis for taxon recognition is a confounding mix of phylogenetic relatedness and some measure of ‘‘degree of divergence’’. Most systematists and evolutionary biologists now advocate classifications that are strictly phylogenetic, in which all named taxa above the species level are monophyletic (Wiley and Lieberman 2011; Vences et al. 2013; Judd et al. 2016). Hence, in contemporary biology textbooks birds are acknowledged to be part of the reptile clade; non-monophyletic groups such as ‘‘Pisces’’ and ‘‘Articulata’’ have been abandoned; and a primary division of flowering plants into ‘‘dicots’’ and monocots is recognized as untenable (Westheide and Rieger 2013, 2015; Freeman et al. 2014; Sadava et al. 2014; Judd et al. 2016). In entomology, paraphyletic groups such as ‘‘Homoptera’’, ‘‘Heterocera’’, and ‘‘Apterygota’’ are no longer part of insect classification (Gullan and Cranston 2014; Beutel et al. 2014). Others, such as Blattodea, have been redefined to encompass all their descendant taxa, and hence avoid paraphyly—in this case by including termites in the cockroach order (Inward et al. 2007). Of course, vernacular terms exist for some paraphyletic assemblages (moths, algae, fish, invertebrates, etc.), but most of them are no longer treated as formal groups in a classification. One could argue that scientific controversies should not be decided by majority rule alone, but there are sound reasons why biological systematists overwhelmingly favor a phylogenetic classification. Such a scheme is simply more informative, accurate, and predictive. Birds really are a kind of modified reptile; to place them in a different group, separate from reptiles, obscures this important fact. Similarly, inclusion of termites in the order Blattodea emphasizes that they are indeed ‘‘social cockroaches’’ and this leads to a more insightful understanding of their biology and evolution (Bell et al. 2007). Excluding termites from Blattodea and putting them in their own order, Isoptera, would be positively misleading. A phylogenetic classification is also, ultimately, more stable: as we refine our understanding of the tree of life, and achieve ever more confident estimates of phylogenetic relationships, systematists are more likely to converge upon a consensus. In a phylogenetic classification not all nodes in the tree of life need to be named, but any group that is namedmust meet the criterion ofmonophyly, and this limits the number of available options (Schmidt-Lebuhn 2012). By contrast, allowing paraphyletic groups opens up a can of worms. How distinct does a divergent ingroup have to be to justify excising it from its containing group and thereby render the latter paraphyletic?Given that rates of evolution are highly variable, and also vary among different classes of characters, there would be no end of argument—never resolved satisfactorily—about whether a given group is ‘‘sufficiently distinct’’ to be removed from its containing clade. & P. S. Ward psward@ucdavis.edu

中文翻译：

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系统发育分类信息丰富、稳定且实用：单系分类群的案例

在本期刊 Seifert 等人最近的评论中。（2016 年）建议回归一种很大程度上被系统论者抛弃的分类学派，其中单系群和并系群都得到了正式承认。这种被称为“进化分类”的方法已被证明是没有吸引力和不切实际的，因为分类群识别的基础是系统发育相关性和某种“差异程度”衡量标准的混杂组合。大多数系统学家和进化生物学家现在提倡严格系统发育的分类，其中所有在物种水平以上命名的分类群都是单系的（Wiley and Lieberman 2011; Vences et al. 2013; Judd et al. 2016）。因此，在当代生物学教科书中，鸟类被认为是爬行动物进化枝的一部分。非单系群，如“双鱼座”和“关节”已被放弃；将开花植物主要分为“双子叶植物”和单子叶植物被认为是站不住脚的（Westheide and Rieger 2013, 2015; Freeman et al. 2014; Sadava et al. 2014; Judd et al. 2016）。在昆虫学中，诸如“同翅目”、“异角目”和“翼翅目”等并系群不再是昆虫分类的一部分（Gullan 和 Cranston 2014；Beutel 等人 2014）。其他物种，例如 Blattodea，已被重新定义为包含它们的所有后代分类群，因此避免并系——在这种情况下，通过将白蚁包括在蟑螂目中（Inward 等人，2007 年）。当然，对于一些并系组合（飞蛾、藻类、鱼、无脊椎动物等），存在白话术语，但它们中的大多数不再被视为分类中的正式群体。有人可能会争辩说，科学争议不应仅由多数规则决定，但生物系统学家压倒性地支持系统发育分类是有充分理由的。这样的方案只是提供更多信息、准确和预测。鸟类确实是一种经过改造的爬行动物；将它们放在与爬行动物分开的不同群体中，掩盖了这一重要事实。同样，将白蚁纳入 Blattodea 目强调它们确实是“社会蟑螂”，这导致对其生物学和进化的更深入了解（Bell 等人，2007 年）。将白蚁排除在 Blattodea 之外并将它们按自己的顺序排列，Isoptera，会产生积极的误导。最终，系统发育分类也更加稳定：随着我们对生命之树的理解不断完善，并且对系统发育关系进行更自信的估计，系统学家更有可能达成共识。在系统发育分类中，并非生命树中的所有节点都需要命名，但任何命名的组都必须满足单系标准，这限制了可用选项的数量（Schmidt-Lebuhn 2012）。相比之下，允许并系群会打开一罐蠕虫。一个发散的内群必须有多明显才能证明将其从其包含的群中剔除，从而使后者成为并系？鉴于进化速度是高度可变的，并且在不同类别的角色之间也有所不同，争论将永无止境——从未令人满意地解决——关于一个给定的群体是否“足够不同”以从其包含的进化枝中移除。和 PS 病房 psward@ucdavis。