Staps, M., & Tarnita, C. E. (2022).
PNAS, 119(18).
Abstract
Task allocation is a central feature of collective organization. Living collective systems, such as multicellular organisms or social insect colonies, have evolved diverse ways to allocate individuals to different tasks, ranging from rigid, inflexible task allocation that is not adjusted to changing circumstances to more fluid, flexible task allocation that is rapidly adjusted to the external environment. While the mechanisms underlying task allocation have been intensely studied, it remains poorly understood whether differences in the flexibility of task allocation can be viewed as adaptive responses to different ecological contexts—for example, different degrees of temporal variability. Motivated by this question, we develop an analytically tractable mathematical framework to explore the evolution of task allocation in dynamic environments. We find that collective flexibility is not necessarily always adaptive, and fails to evolve in environments that change too slowly (relative to how long tasks can be left unattended) or too quickly (relative to how rapidly task allocation can be adjusted). We further employ the framework to investigate how environmental variability impacts the internal organization of task allocation, which allows us to propose adaptive explanations for some puzzling empirical observations, such as seemingly unnecessary task switching under constant environmental conditions, apparent task specialization without efficiency benefits, and high levels of individual inactivity. Altogether, this work provides a general framework for probing the evolved diversity of task allocation strategies in nature and reinforces the idea that considering a system’s ecology is crucial to explaining its collective organization.
Significance
A central problem in evolutionary biology is explaining variation in the organization of task allocation across collective systems. Why do human cells irreversibly adopt a task during development (e.g., kidney vs. liver cell), while sponge cells switch between different cell types? And why have only some ant species evolved specialized castes of workers for particular tasks? Although it seems reasonable to suppose that such differences reflect, at least partially, the different ecological pressures that systems face, there is no general understanding of how a system’s dynamic environment shapes its task allocation. To this end, we develop a general mathematical framework that reveals how simple ecological considerations could potentially explain cross-system variation in task allocation—including in flexibility, specialization, and (in)activity.
Here are some thoughts:
Of interest to psychologists, this paper by Staps and Tarnita provides a formal ecological and evolutionary framework for understanding the adaptive value of behavioral flexibility, specialization, and inactivity, both in individuals and in groups.
The model demonstrates that collective flexibility in task allocation—akin to cognitive and behavioral flexibility in humans—is not always advantageous and instead depends critically on the dynamics of the environment. This offers a principled explanation for why some systems, from neural networks to human teams, might exhibit rigid specialization while others maintain fluid, generalist roles.
Furthermore, the work gives functional explanations for puzzling behaviors that seem suboptimal from a productivity standpoint, such as frequent task-switching even in stable conditions and high levels of inactivity. These insights can inform psychological research on motivation, team dynamics, and organizational behavior by suggesting that such "inefficiencies" may be evolutionary adaptations for enhancing responsiveness to future change.
The framework bridges the gap between ultimate, evolutionary causes and proximate, mechanistic explanations of how individuals and groups allocate cognitive and behavioral resources.