Paleontology for conservation Human activities are leading to broad species and system declines. Prevention of such declines has led us to focus on either protection for species or protection for ecosystem function. Looking at past patterns of species and system change can help to inform our understanding of the long-term impacts of these strategies. Blanco et al. studied mammals from the last 21 million years on the Iberian Peninsula, finding long periods of functional stasis, even in the face of taxonomic variability (see the Perspective by Roopnarine and Banker). Functional ecosystems were more resistant to ecosystem collapse. Science , this issue p. 300 ; see also p. 237