How did rats originate? - briefly
Rats belong to the murid lineage that diversified in Asia during the Miocene epoch, giving rise to the genus Rattus about 10–12 million years ago. Human‑mediated transport in recent centuries spread them globally.
How did rats originate? - in detail
Rats belong to the family Muridae, subfamily Murinae, which diversified during the late Oligocene to early Miocene (≈ 23–30 million years ago). Molecular phylogenies place the split between the lineage leading to modern Rattus and its closest relatives, such as Bandicota and Nesokia, at roughly 12 million years ago. The earliest unequivocal rat fossils appear in the late Miocene strata of Asia, notably the species Rattus lamottei from the Siwalik Hills (≈ 10 million years ago). These specimens exhibit dental morphology characteristic of the genus, including high‑crowned molars and a distinctive pattern of enamel folds.
Key points in the evolutionary history:
- Origin in South‑East Asia: genetic diversity peaks in the Indo‑Burmese region, indicating an ancestral population that radiated outward.
- Divergence of major clades: the Rattus rattus (black rat) and Rattus norvegicus (brown rat) lineages separated around 1.5 million years ago, as inferred from mitochondrial DNA.
- Expansion with human activity: archaeological sites in the Mediterranean (≈ 2 kyr BP) and later in Europe contain rat remains coincident with the spread of agriculture and trade routes.
- Adaptation to commensal habitats: morphological changes, such as reduced body size and increased reproductive rate, facilitated survival in human‑dominated environments.
Fossil records from the Pleistocene show rapid geographic spread across Eurasia, followed by introduction to the Americas during the 16th century via European ships. Contemporary populations retain signatures of these historic dispersal events, observable in genome‑wide analyses that reveal admixture between native Asian lineages and introduced European stocks.
«The rat’s success derives from a combination of ecological flexibility, high fecundity, and close association with humans», notes a 2022 phylogeographic study. This synthesis of paleontological data, molecular clocks, and archaeological evidence provides a comprehensive picture of rat origins and subsequent global distribution.