Abstract Language change and biological evolution are sufficiently similar that biologists and linguists often face similar challenges in reconstructing paths of historical change connecting different species or languages. Tracing evolutionary change over time requires us to consider how shared features have been modified in different lineages since they shared a common ancestor, and this means we have to be able to establish meaningful comparability between traits. In some cases, we may wish to understand how the same ancestral trait has been modified in each lineage in response to different pressures. But in other cases, we may wish to ask whether particular traits often arise in response to certain circumstances. Biologists must therefore consider different reasons for similarities between species, and choose to compare those traits that are relevant to the story they want to tell. To reconstruct histories of change, we need to compare homologous traits (those similar due to shared ancestry). But comparing analogous traits (independently derived but similar traits) highlights how separate evolutionary lineages can find similar solutions to common problems. I will illustrate the importance of comparability in constructing evolutionary explanations using one of the more obscure yet fascinating examples of Charles Darwin’s scientific researches, his multi-volume taxonomic treatise on barnacles. Darwin faced the challenge of how to explain the evolutionary trajectory of unique and highly modified traits that appear to have no equivalents in related taxa. He did this by tracing the development of unique traits within growing individuals, looking for variation in these strange adaptations between individuals, and comparing them across species that varied in their degree of modification from their ancestor. Using meticulous observations to establish comparability, even in such an incomparable animal as the barnacle, he could reconstruct plausible evolutionary explanations for even the most bizarrely modified traits, such as the presence of parasitic males and the invention of the cement that sticks barnacles to rocks, boats and whales. Nowadays, scientists increasingly rely on DNA evidence to trace evolutionary paths, which brings both advantages and challenges in establishing comparability. Even if you, like most people, are not particularly interested in barnacles, Darwin’s underappreciated taxonomic work is a surprisingly good place to go to if you want to think about the issue of comparability and why it matters to understanding evolution.

中文翻译：

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进化生物学中的可比性：达尔文藤壶的案例

摘要语言变化和生物进化非常相似，生物学家和语言学家在重建连接不同物种或语言的历史变化路径时经常面临相似的挑战。追踪随着时间变化的进化变化，需要我们考虑共享的特征如何在不同的世系中共享，因为它们共享一个共同的祖先，这意味着我们必须能够在特征之间建立有意义的可比性。在某些情况下，我们可能希望了解如何针对不同的压力在每个血统中修改了相同的祖先特征。但是在其他情况下，我们不妨问一问，是否在某些情况下会经常出现某些特质。因此，生物学家必须考虑物种之间相似性的不同原因，并选择比较与他们想讲的故事相关的特征。要重建变化的历史，我们需要比较同源特征（由于共同的祖先而相似）。但是比较相似的特征（独立衍生但相似的特征）强调了不同的进化谱系如何能够找到共同问题的相似解决方案。我将使用查尔斯·达尔文（Charles Darwin）的科学研究中较为晦涩但引人入胜的例子之一，即他关于藤壶的多卷分类学论文，来说明可比性在构建进化解释中的重要性。达尔文面临着一个挑战，即如何解释独特且经过高度修饰的特征的进化轨迹，这些特征在相关的分类单元中似乎是不存在的。他通过追踪成长中个体独特性的发展来做到这一点，寻找个体之间这些奇怪适应的变异，并将其与祖先修饰程度不同的物种进行比较。即使是在像藤壶这样的无与伦比的动物中，他也可以通过细致的观察来建立可比性，甚至可以对最怪异的性状进行合理的进化解释，例如寄生虫的存在以及发明了将藤壶粘在岩石上的水泥的发明，船和鲸鱼。如今，科学家越来越依赖DNA证据来追踪进化路径，这在建立可比性方面既带来了优势，也带来了挑战。即使您像大多数人一样，对藤壶并不特别感兴趣，