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  • The White-Throated Rail

    The White-Throated Rail | Photo: Wikimediacommons

Published 11 May 2019

This remarkably uncommon process is classified as iterative evolution, a process in which the same ancestor evolves into the same species at different points in history.

A study published Wednesday reveals that the white-throated rail that inhabits the Aldabra Atoll in the Indian Ocean has repeated the 'course of evolution' after being wiped from existence some 136,000 years ago. 

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The bird's lineage originated in Madagascar, flew to Aldabra some 250 miles away, and likely remained on the island due to lack of predators. Another result of the newfound safety is that the bird evolved to become flightless. 

A flood reportedly wiped the species from the island, but when land reemerged, another flock from Madagascar arrived and begin the 'course of evolution' again. 

Researchers have found fossils of the bird from before and after the floods, both of which showed that the 'course of evolution' resulted in the bird losing the ability to fly.

The white-throated rail continues to inhabit Aldabra.

This remarkably uncommon process is classified as iterative evolution, a process in which the same ancestor evolves into the same species at different points in history.

This specific event is regarded as the "most significant" process in the bird kingdom.

"We know of no other example in rails, or of birds in general, that demonstrates this phenomenon so evidently," a researcher at the University of Portsmouth, David Martill, noted.

The Madagascar-native parent species of the rail experienced consistent surges in population, which would result in the birds migrating from the island. The birds that flew north or south ended up drowning in the Indian Ocean, and those that went west were met by predators in Africa.

"Conditions were such on Aldabra, the most important being the absence of terrestrial predators and competing mammals, that a rail was able to evolve flightlessness independently on each occasion," Martill explained. 

The Aldabra rail is the last surviving flightless bird in the Indian Ocean.

Due to human inhabitation of the island - along with pets such as cats and dogs, that enjoy eating birds - the potential for iterative evolution to occur for the species on the island again is highly unlikely. 

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