Kin Selection and Inclusive Fitness in Plant Evolution: Mechanisms and Empirical Insights

Darwin’s early puzzlement about sterile castes helped catalyse inclusive-fitness theory and kin selection, providing a genetic framework for the evolution of helping behaviours. This review integrates theoretical models and empirical studies that apply inclusive-fitness logic to plant reproductive strategies, concentrating on sibling rivalry, maternal counter-strategies (polyembryony, endosperm function, locule architecture), and kin recognition mediated by root exudates and light-quality cues. Studies show how parent–offspring conflict predicts divergent optima for per-seed investment and brood size and how maternal mechanisms can compensate for or mitigate damaging within-fruit competition. We highlight methodological limitations of controlled studies, including Jensen’s inequality and the ecological differences between artificial substrates and natural soils, and recommend mechanism-focused approaches such as exudate exposure assays and molecular profiling. Finally, we explore agronomic implications, arguing that inclusive-fitness perspectives can inform breeding for cooperative ideotypes and the design of varietal mixtures, while emphasizing that field validation is essential. Overall, inclusive-fitness theory provides a powerful interpretive and predictive toolkit for plant evolutionary biology and sustainable agriculture.