Plant Hormone Regulation of Competitive Growth: Implications for Agriculture and Inclusive Fitness

While “survival of the fittest” implies that competition is the main driver of evolution, cooperation and altruism are also widespread in nature, even among plants. This suggests that natural selection favors regulatory systems that balance competitive growth with restraint, depending on context. We propose that plant hormones are key mediators of this balance, acting along a spectrum from competition to cooperation. Based on evidence from developmental, ecological, and evolutionary studies, we classify major plant hormones by their roles in competitive behavior: auxin, gibberellins, and brassinosteroids drive competitive foraging and resource acquisition, while cytokinins, abscisic acid, strigolactones, ethylene, salicylic acid, and jasmonate are linked to growth restraint, resource conservation, and communal defense. This functional partitioning reflects a modular hormonal architecture that allows plants to adapt flexibly to their environment and social context. We explore how this classification could inform the use of plant hormones in agriculture and advance research in plant kin selection and inclusive fitness.