Important evolutionary events such as the Cambrian Explosion have inspired many attempts at explanation: why do they happen when they do? What shapes them, and why do they eventually come to an end? However, much less attention has been paid to the idea of a ‘null hypothesis’—that certain features of such diversifications arise simply through their statistical structure. Such statistical features also appear to influence our perception of the timing of these events. Here, we show in particular that study of unusually large clades leads to systematic overestimates of clade ages from some types of molecular clocks, and that the size of this effect may be enough to account for the puzzling mismatches seen between these molecular clocks and the fossil record. Our analysis of the fossil record of the late Ediacaran to Cambrian suggests that it is likely to be recording a true evolutionary radiation of the bilaterians at this time, and that explanations involving various sorts of cryptic origins for the bilaterians do not seem to be necessary.

像寒武纪大爆发这样的重要进化事件激发了许多解释的尝试：为什么它们会在发生时发生？是什么塑造了它们，为什么它们最终会结束？然而，人们对“零假设”这一概念的关注要少得多，即这种多样化的某些特征只是通过其统计结构而产生的。这些统计特征似乎也会影响我们对这些事件发生时间的看法。在这里，我们特别表明，对异常大的进化枝的研究导致对某些类型的分子钟的进化枝年龄的系统性高估，并且这种效应的大小可能足以解释这些分子钟和化石之间令人费解的不匹配。记录。我们对埃迪卡拉晚期至寒武纪化石记录的分析表明，它很可能记录了此时两侧对称动物的真实进化辐射，并且涉及两侧对称动物各种神秘起源的解释似乎没有必要。