Seed Dispersal and Crop Domestication: Shattering, Germination and Seasonality in Evolution Under Cultivation

Abstract The transition between wild plant forms and domesticated species can be considered an evolutionary adaptation by plants in response to a human driven ecology. Evidence from archaeobotany and genetics is providing deeper insight into this evolutionary process in terms of its scale, mechanism and parallelism between species. The evidence indicates that the timescale of this evolution was considerably longer than previously supposed, raising questions about the mode of human mediated selection pressure and increasing the importance of the role of pre‐domestication cultivation. Different selection pressures were chronologically separated into at least three stages, each important at different points of the evolutionary process affecting different traits. Early selection pressures were ultimately driven by the pre‐domestication sowing activities affecting the polygenically controlled germination and seed size traits. Later, in the second stage, release of natural selection pressures of dispersal requirements led to modification of architecture such as awns loss of awns and increase in dispersal unit size. The loss of dispersal requirement combined with positive pressure through harvesting practice led to the typically monogenically controlled non‐shattering phenotypes. At the tertiary stage new selection pressures were imposed with changing climate caused by movement of the crops into different latitudes, resulting in typically monogenically controlled aseasonal phenotypes. The genetic evidence shows in most cases that genetically similar mechanisms have been affected in different plant species implying an evolutionary convergence in response to adaptation to human ecology. These adaptations can be considered various types of heterochrony; a mechanism of major importance generally in plant evolution.