Tempo and Mode in Evolution
TL;DR
Three evolutionary speeds—bradytely, horotely, tachytely—explain why lineages explode when entering new adaptive zones then stabilize as niches fill.
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Foundational work that unified paleontology and genetics into modern evolutionary theory. Introduced the concepts of adaptive zones, quantum evolution, and tempo categories (bradytely, horotely, tachytely) that still structure macroevolutionary research. Central to the book's treatment of how market entry timing parallels ecological opportunity.
Key Findings from Simpson (1944)
- Three evolutionary tempos: bradytely (slow), horotely (standard, 90% of record), tachytely (rapid)
- Adaptive zones explain why lineages radiate when entering new ecological space
- Quantum evolution describes rapid 'all-or-nothing' transitions between adaptive zones
- Radiation slows as niches fill and competition intensifies
- Mammalian radiation after dinosaur extinction exemplifies tachytelic tempo