Data from: Solving the paradox of stasis: squashed stabilizing selection and the limits of detection

Despite the potential for rapid evolution, stasis is commonly observed over geological timescales – the so-called “paradox of stasis.” This paradox would be resolved if stabilizing selection were common, but stabilizing selection is infrequently detected in natural populations. We hypothesize a simple solution to this apparent disconnect: stabilizing selection is hard to detect empirically once populations have adapted to a fitness peak. To test this hypothesis, we developed an individual-based model of a population evolving under an invariant stabilizing fitness function. Stabilizing selection on the population was infrequently detected in an “empirical” sampling protocol, because (1) trait variation was low relative to the fitness peak breadth; (2) non-selective deaths masked selection; (3) populations wandered around the fitness peak; and (4) sample sizes were typically too small. Moreover, the addition of negative frequency-dependent selection further hindered detection by flattening or even dimpling the fitness peak, a phenomenon we term “squashed stabilizing selection”. Our model demonstrates that stabilizing selection provides a plausible resolution to the paradox of stasis despite its infrequent detection in nature. The key reason is that selection “erases its traces”: once populations have adapted to a fitness peak, they are no longer expected to exhibit detectable stabilizing selection.尽管演化具备快速发生的潜力，但在地质时间尺度上却常观测到演化停滞现象——即所谓的“停滞悖论（paradox of stasis）”。若稳定选择（stabilizing selection）普遍存在，这一悖论本应得以解决，但在自然种群中却极少能检测到稳定选择的存在。我们针对这一明显的矛盾提出了一个简单的解决方案：当种群适应至适应峰（fitness peak）后，稳定选择在实证层面便难以被检测到。为验证该假说，我们构建了一个基于个体的模型（individual-based model），模拟种群在恒定的稳定适应度函数下的演化过程。在“经验采样方案（empirical sampling protocol）”下，该种群的稳定选择极少被检测到，原因如下：(1) 相较于适应峰宽度，性状变异（trait variation）程度较低；(2) 非选择性死亡（non-selective deaths）掩盖了选择作用；(3) 种群在适应峰附近随机游走；(4) 样本规模通常过小。此外，引入负频率依赖选择（negative frequency-dependent selection）会通过压低甚至凹陷适应峰的方式进一步阻碍检测，我们将这一现象命名为“压缩型稳定选择（squashed stabilizing selection）”。本模型证明，尽管稳定选择在自然界中极少被检测到，但它仍为停滞悖论提供了一个合理的解释。其核心原因在于选择会“抹去自身痕迹”：一旦种群适应至适应峰，便不再会表现出可被检测到的稳定选择。