Life histories are not just fast or slow

Life history strategies, which combine schedules of survival, development, and reproduction, shape how natural selection acts on species’ heritable traits and organismal fitness. Comparative analyses have historically ranked life histories along a fast–slow continuum, describing a negative association between time allocation to reproduction and development versus survival. However, higher-quality, more representative data and analyses have revealed that life history variation cannot be fully accounted for by this single continuum. Moreover, studies often do not test predictions from existing theories and instead operate as exploratory exercises. To move forward, we offer three recommendations for future investigations: standardizing life history traits, overcoming taxonomic siloes, and using theory to move from describing to understanding life history variation across the Tree of Life.