Data from: The evolutionary origin of somatic cells under the dirty work hypothesis

Reproductive division of labor is a hallmark of multicellular organisms. However, the evolutionary pressures that give rise to delineated germ and somatic cells remain unclear. Here we propose a hypothesis that the mutagenic consequences associated with performing metabolic work favor such differentiation. We present evidence in support of this hypothesis gathered using a computational form of experimental evolution. Our digital organisms begin each experiment as undifferentiated multicellular individuals, and can evolve computational functions that improve their rate of reproduction. When such functions are associated with moderate mutagenic effects, we observe the evolution of reproductive division of labor within our multicellular organisms. Specifically, a fraction of the cells remove themselves from consideration as propagules for multicellular offspring, while simultaneously performing a disproportionately large amount of mutagenic work, and are thus classified as soma. As a consequence, other cells are able to take on the role of germ, remaining quiescent and thus protecting their genetic information. We analyze the lineages of multicellular organisms that successfully differentiate and discover that they display unforeseen evolutionary trajectories: cells first exhibit developmental patterns that concentrate metabolic work into a subset of germ cells (which we call “pseudo-somatic cells”) and later evolve to eliminate the reproductive potential of these cells and thus convert them to actual soma. We also demonstrate that the evolution of somatic cells enables phenotypic strategies that are otherwise not easily accessible to undifferentiated organisms, though expression of these new phenotypic traits typically includes negative side effects such as aging.生殖劳动分工是多细胞生物的标志性特征。然而，催生界限分明的生殖细胞（germ cell）与体细胞（somatic cell）的进化压力仍未阐明。本文提出一项假说：与执行代谢工作相关的诱变后果，会推动此类细胞分化。我们借助计算式实验演化方法收集到的证据，为该假说提供了支撑。本研究中的数字化生物在每项实验初始阶段均为未分化的多细胞个体，可演化出提升自身繁殖速率的计算功能。当此类功能伴随适度诱变效应时，我们观察到多细胞生物体内生殖劳动分工的演化过程。具体而言，一部分细胞不再作为多细胞后代繁殖体（propagules）的候选对象，同时承担了比例极高的诱变工作，因此被归类为体细胞。作为此变化的结果，其余细胞得以承担生殖细胞的角色，保持静息状态以保护自身遗传信息。我们对成功实现细胞分化的多细胞生物谱系进行分析后发现，它们展现出了未曾预料的演化轨迹：细胞首先呈现出将代谢工作集中于部分生殖细胞的发育模式——我们将此类细胞称为“伪体细胞（pseudo-somatic cells）”，后续则演化出消除这些细胞的繁殖潜能，使其转化为真正的体细胞。我们还证实，体细胞的演化使得未分化生物难以轻易获取的表型策略成为可能，尽管这些新表型性状的表达通常会伴随衰老等负面影响。