The article by G. M. Hewitt discusses the genetic consequences of climatic oscillations during the Quaternary period, which have significantly influenced species evolution and distribution. The scale and frequency of these climatic changes have led to major extinctions and repeated range shifts, with spatial effects varying by latitude and topography. High latitudes experienced extensive extinctions and recolonization, while altitudinal shifts and complex refugia were more common in lower latitudes. Population dynamics varied with life history and geography, and the current genetic composition of populations and species reflects these past dynamics. Phylogeographic studies using DNA have become increasingly common, revealing distinct genetic clades in arctic, temperate, and tropical regions. Arctic species show distinct shallow genetic clades with common geographical boundaries, while temperate species in Europe and North America exhibit deeper DNA divergence, indicating their presence over multiple Ice Ages. Tropical montane regions contain deeply diverged lineages, often in small geographical areas, suggesting survival from the Pliocene. The article highlights the importance of combining fossil and genetic studies to better understand refugial biodiversity.The article by G. M. Hewitt discusses the genetic consequences of climatic oscillations during the Quaternary period, which have significantly influenced species evolution and distribution. The scale and frequency of these climatic changes have led to major extinctions and repeated range shifts, with spatial effects varying by latitude and topography. High latitudes experienced extensive extinctions and recolonization, while altitudinal shifts and complex refugia were more common in lower latitudes. Population dynamics varied with life history and geography, and the current genetic composition of populations and species reflects these past dynamics. Phylogeographic studies using DNA have become increasingly common, revealing distinct genetic clades in arctic, temperate, and tropical regions. Arctic species show distinct shallow genetic clades with common geographical boundaries, while temperate species in Europe and North America exhibit deeper DNA divergence, indicating their presence over multiple Ice Ages. Tropical montane regions contain deeply diverged lineages, often in small geographical areas, suggesting survival from the Pliocene. The article highlights the importance of combining fossil and genetic studies to better understand refugial biodiversity.