Philosophy Department, Macquarie University, Sydney, Australia.
Department of Philosophy & Charles Perkins Centre, The University of Sydney, Sydney, Australia.
Elife. 2022 Aug 17;11:e73715. doi: 10.7554/eLife.73715.
Evolutionary transitions in individuality (ETIs) involve the formation of Darwinian collectives from Darwinian particles. The transition from cells to multicellular life is a prime example. During an ETI, collectives become units of selection in their own right. However, the underlying processes are poorly understood. One observation used to identify the completion of an ETI is an increase in collective-level performance accompanied by a decrease in particle-level performance, for example measured by growth rate. This seemingly counterintuitive dynamic has been referred to as fitness decoupling and has been used to interpret both models and experimental data. Extending and unifying results from the literature, we show that fitness of particles and collectives can never decouple because calculations of fitness performed over appropriate and equivalent time intervals are necessarily the same provided the population reaches a stable collective size distribution. By way of solution, we draw attention to the value of mechanistic approaches that emphasise traits, and tradeoffs among traits, as opposed to fitness. This trait-based approach is sufficient to capture dynamics that underpin evolutionary transitions. In addition, drawing upon both experimental and theoretical studies, we show that while early stages of transitions might often involve tradeoffs among particle traits, later-and critical-stages are likely to involve the rupture of such tradeoffs. Thus, when observed in the context of ETIs, tradeoff-breaking events stand as a useful marker of these transitions.
个体进化转变（ETIs）涉及从达尔文粒子形成达尔文主义集合体。从细胞到多细胞生命的转变就是一个主要的例子。在 ETI 期间，集合体本身成为选择的单位。然而，潜在的过程还不太清楚。用于识别 ETI 完成的一个观察是集合体水平性能的增加伴随着粒子水平性能的下降，例如通过增长率来衡量。这种看似违反直觉的动态被称为适应度解耦，已被用于解释模型和实验数据。扩展和统一文献中的结果，我们表明，粒子和集合体的适应度永远不会解耦，因为在适当和等效的时间间隔内进行的适应度计算在种群达到稳定的集合体大小分布的情况下必须是相同的。作为解决方案，我们提请注意强调特征和特征之间权衡的机制方法的价值，而不是适应度。这种基于特征的方法足以捕捉支持进化转变的动态。此外，通过实验和理论研究，我们表明，虽然转变的早期阶段可能经常涉及粒子特征之间的权衡，但后期和关键阶段可能涉及这种权衡的破裂。因此，当在 ETI 的背景下观察到这种情况时，打破权衡的事件成为这些转变的有用标记。
