Turnover-pulse hypothesis

The turnover-pulse hypothesis, formulated by paleontologist Elisabeth Vrba, suggests that major changes to the climate or ecosystem often result in a period of rapid extinction and high turnover of new species (a "pulse") across multiple different lineages. Changes may include climate change, tectonic plate shifting, and catastrophes, among other things. It can be seen as an extension of the concept of evolutionary radiation from a single to a multi-clade context.

Contents

Theory

Ecosystems periodically experience significant disruptions which cause mass extinctions and speciation. Vrba proposes that changes in the climate, through their effect on the physical environment, result in the "division of populations into geographically and genetically isolated groups", which subsequently evolve into separate species. She also predicts that within an ecosystem this should occur for different groups of animals at roughly the same time, creating a "synchronous pulse" across multiple lineages.

The hypothesis was developed to explain the different patterns of evolution seen in African antelopes. Vrba argued that the mammalian fauna of East Africa experienced a rapid burst of extinction and speciation between 2.8Ma and 2.5Ma, caused by a large fluctuation in temperature. During this event, so the hypothesis states, many species attempted to move from their now uninhabitable habitats and later developed different adaptations in their new environments, evolving into different species, such as the antelopes investigated by Vrba, which evolved from woodland browsers to grassland grazers. Vrba's support for the idea that different clades would all adapt synchronously and alongside climate events came from the fossil record of rodents from the Omo river valley.

Hominins

Vrba later proposed these changes as the spark for the emergence of the Homo lineage, as distinct from other hominins, which is dated to around this time. This aligns with the savannah hypothesis (or "aridity hypothesis"), which suggests that increasing aridity led to the growth and expansion of the savannah, requiring the hominins to come down from the trees and walk on two legs. The earliest archaeological sites containing tools also date to this period. However, it is still possible that the genus Homo had already evolved before the climate event.

Criticism

The main opposing viewpoint is the ...read more

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