Understanding why biodiversity is unevenly distributed is fundamental to ecology and evolution. Should we look to contemporary climate to explain where species diversity is highest, or look deeper into the past? Jongsma et al. (2026) tackled this question in the Lower Guinean Forests of Central Africa, a biodiversity hotspot stretching from Nigeria through Gabon and the Republic of Congo. The researchers developed a quantitative approach to map forest stability since the Pleistocene. Using ecological niche models for 10 forest-obligate frog species projected across 257 time-slices spanning 2.58 million to 20,000 years ago, they created the first continuous stability map for the region. They then tested whether this deep-time stability or contemporary climate better explained current patterns of diversity in 124 species of Afrobatrachian frogs. Pleistocene forest stability explained 65–71% of spatial variance in species richness and phylogenetic diversity, which far exceeds contemporary temperature, precipitation, or forest cover. Even within current rainforest, diversity declined sharply with distance from historically stable areas, indicating that species distributions remain far from equilibrium with present-day conditions. Less than 15% of the most stable forests are currently protected. Strategically expanding protected areas to include these past stable regions could increase mean amphibian richness under protection by nearly one-fifth. This study demonstrates that effective conservation planning should consider deep-time habitat stability alongside current environmental conditions.

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