Although the role of Earth’s orbital variations in driving global climate cycles has long been recognized, their effect on evolution is hitherto unknown. The fossil remains of coccolithophores, a key calcifying phytoplankton group, enable a detailed assessment of the effect of cyclic orbital-scale climate changes on evolution because of their abundance in marine sediments and the preservation of their morphological adaptation to the changing environment^1,2. Evolutionary genetic analyses have linked broad changes in Pleistocene fossil coccolith morphology to species radiation events³. Here, using high-resolution coccolith data, we show that during the last 2.8 million years the morphological evolution of coccolithophores was forced by Earth’s orbital eccentricity with rhythms of around 100,000 years and 405,000 years—a distinct spectral signature to that of coeval global climate cycles⁴. Simulations with an Earth System Model⁵ coupled with an ocean biogeochemical model⁶ show a strong eccentricity modulation of the seasonal cycle, which we suggest directly affects the diversity of ecological niches that occur over the annual cycle in the tropical ocean. Reduced seasonality in surface ocean conditions favours species with mid-size coccoliths, increasing coccolith carbonate export and burial; whereas enhanced seasonality favours a larger range of coccolith sizes and reduced carbonate export. We posit that eccentricity pacing of phytoplankton evolution contributed to the strong 405,000-year cyclicity that is seen in global carbon cycle records.

尽管地球轨道变化在驱动全球气候循环中的作用早已得到认可，但它们对进化的影响迄今仍是未知的。球石藻的化石残骸是一种关键的钙化浮游植物群，能够详细评估循环轨道尺度气候变化对进化的影响，因为它们在海洋沉积物中的丰富性以及它们对不断变化的环境的形态适应性的保存^1,2。进化遗传分析已将更新世化石球石形态的广泛变化与物种辐射事件联系起来³. 在这里，我们使用高分辨率球石数据表明，在过去 280 万年中，球石藻的形态演化是由地球轨道离心率造成的，其节律约为 100,000 年和 405,000 年——与同时代全球气候周期的光谱特征截然不同⁴ . 地球系统模型⁵与海洋生物地球化学模型^6的模拟显示出季节性周期的强烈偏心率调制，我们认为这直接影响热带海洋年度周期中发生的生态位的多样性。减少地表海洋条件的季节性有利于具有中等大小的球石的物种，增加了碳酸盐的出口和埋葬；而增强的季节性有利于更大范围的球粒石尺寸和减少碳酸盐的出口。我们假设浮游植物进化的偏心率促成了全球碳循环记录中可见的 405,000 年的强烈循环。