Selection of the Fittest or Selection of the Luckiest: Simulation Software and Datasets

Natural selection is commonly assumed to become more effective as it becomes stronger. However, selection acts on phenotypes rather than directly on genotypes, and phenotypic success is inherently noisy. Here we study how this mismatch shapes long-term evolutionary dynamics. Using a minimal stochastic model in which individuals inherit genetic fitness while selection acts on noisy phenotypic expressions, we show that increasing selection strength accelerates adaptation only up to a critical threshold. Beyond this point, stronger selection paradoxically slows evolutionand erodes genetic diversity by favoring the luckiest individuals rather than the genetically fittest.We identify two distinct evolutionary regimes—selection of the fittest and selection of the luckiest—separated by a sharp transition. This transition corresponds to a previously unrecognized change in the structure of traveling fitness waves, from semipulled to fully pulled fronts, with profound consequences for adaptation speed and genealogical structure. The attached .zip file contains the simulation software and the datasets used for the paper (see an arxiv preprint linked below).人们通常认为，自然选择（natural selection）的效力会随选择强度的提升而增强。然而，自然选择作用于表型（phenotype）而非直接作用于基因型（genotype），且表型的适应性表现本身存在固有噪声。本研究旨在探究这种错配如何塑造长期进化动力学过程。本研究采用一个极简随机模型（stochastic model）：个体继承遗传适合度，而自然选择作用于带有噪声的表型表达。研究结果表明，提升选择强度仅会在达到临界阈值前加快适应速率；越过该阈值后，更强的选择反而会反常地延缓进化进程，并通过青睐运气更佳的个体而非遗传适合度更高的个体，侵蚀种群的遗传多样性。我们识别出两种截然不同的进化模式——‘适者选择’与‘幸运者选择’，二者由一次尖锐的转变过程分隔开来。该转变对应着行进适合度波结构从前未被认知的变化：从半牵引前沿（semipulled fronts）转变为全牵引前沿（fully pulled fronts），这对适应速率与谱系结构均会产生深远影响。附件的.zip压缩包包含本文所用的模拟软件与数据集（详见下文链接的arXiv预印本）。