Impacts of speciation and extinction measured by an evolutionary decay clock

The hypothesis that destructive mass extinctions enable creative
evolutionary radiations (creative destruction) is central to classic
concepts of macroevolution[1,2]. However, the relative impacts of
extinction and radiation on the co-occurrence of species have not been
directly quantitatively compared across the Phanerozoic eon. Here we apply
machine learning to generate a spatial embedding (multidimensional
ordination) of the temporal co-occurrence structure of the Phanerozoic
fossil record, covering 1,273,254 occurrences in the Paleobiology Database
for 171,231 embedded species. This facilitates simultaneous comparison of
macroevolutionary disruptions, using measures independent of secular
diversity trends. Among the 5% most significant periods of disruption, we
identify the ‘big five’ mass extinction events[2], seven additional mass
extinctions, two combined mass extinction–radiation events and 15 mass
radiations. In contrast to narratives that emphasize post-extinction
radiations[1,3], we find that the proportionally most comparable mass
radiations and extinctions (such as the Cambrian explosion and the
end-Permian mass extinction) are typically decoupled in time, refuting any
direct causal relationship between them. Moreover, in addition to
extinctions[4], evolutionary radiations themselves cause evolutionary
decay (modelled co-occurrence probability and shared fraction of species
between times approaching zero), a concept that we describe as destructive
creation. A direct test of the time to over-threshold macroevolutionary
decay[4] (shared fraction of species between two times ≤ 0.1), counted by
the decay clock, reveals saw-toothed fluctuations around a Phanerozoic
mean of 18.6 million years. As the Quaternary period began at a
below-average decay-clock time of 11 million years, modern extinctions
further increase life’s decay-clock debt.

破坏性大规模灭绝驱动创新性演化辐射（即创造性毁灭，creative destruction）这一假说，是宏观演化经典理论的核心[1,2]。然而，在整个显生宙（Phanerozoic eon）中，灭绝与辐射对物种共现模式的相对影响，尚未被直接开展定量对比。本研究借助机器学习方法，对覆盖古生物学数据库（Paleobiology Database）中171231个嵌入物种的1273254条化石出现记录的显生宙化石记录时间共现结构，生成空间嵌入（spatial embedding，多维排序multidimensional ordination）。该分析框架无需依赖长期多样性演化趋势，即可同时对比宏观演化扰动事件。在占比5%的最显著扰动时段中，我们识别出‘五大’生物大灭绝事件[2]、7次额外的大规模灭绝事件、2次兼具灭绝与辐射特征的复合事件，以及15次大规模辐射事件。不同于强调灭绝后辐射的相关论述[1,3]，本研究发现，比例上最具可比性的大规模辐射与灭绝事件（如寒武纪生命大爆发与二叠纪末大灭绝）在时间上通常是解耦的，这驳斥了二者之间存在直接因果关系的观点。此外，除灭绝事件[4]外，演化辐射本身也会引发演化衰退——即模拟得到的共现概率与时段间物种共享比例趋近于零，我们将这一概念命名为‘破坏性创造’（destructive creation）。通过衰变时钟（decay clock）统计的跨阈值宏观演化衰退[4]直接检验，即两时段间物种共享比例≤0.1，结果显示，显生宙平均衰退时钟时长为1860万年，期间存在锯齿状波动。第四纪（Quaternary period）起始时的衰退时钟时长为1100万年，低于平均水平，而现代物种灭绝进一步加剧了生命的衰退时钟负债。