According to evolutionary theory, all   organisms evolve from a single common ancestor. Phylogenetic trees provide an   elegant way to depict hypothesized ancestor–descendant relationships among   groups of extant, or in some cases extinct, taxa, including all intermediate   ancestors. In fact, the essence of all comparative methods lies in the   varying degrees of shared ancestry among species that determine the expected   similarity in phenotypes (Felsenstein 1985; Harvey and Pagel 1991). Given   that phylogenies provide the necessary information about ancestor–descendant   relationships, they are essential to any comparative analysis and each of   them requires at least one phylogenetic hypothesis to be taken into account.   Ultimately, the evolutionary conclusions will depend on the phylogeny used in   the study.

根据进化理论，所有的生物体都是从一个共同祖先进化而来的。系统发生树提供了一种精巧的方式来描述现生类群通过假设的共同祖先连接关系，当然，在某些情况下也可以描述灭绝的分类群之间的关系。事实上，所有比较方法的本质在于决定表型预期相似性的物种之间共享祖先的不同程度（Felsenstein 1985; Harvey and Pagel 1991）。鉴于系统发育学提供了有关祖先-后代关系的必要信息，它们对于任何比较分析都是必不可少的，而且每一个都需要至少考虑一个系统发育假说。最终，进化结论将取决于研究中使用的系统发育关系。