"Roughly 136,000 years ago, its ancestors - white-throated rails from Madagascar - flew to Aldabra and found a predator-free paradise; no sharp-toothed prowlers or featherless bipeds with pointy sticks. And so, the rails evolved into flightless versions. Why waste effort and energy on flying when there's no point? Then came a catastrophic flood. The island went underwater. The rails couldn't fly, and they couldn't swim. They went extinct."
"And then, after the seas receded, something eerie happened. More rails flew back - their distant ancestors, still strong in Madagascar, made the same flight again. And the story repeated itself. The rails lost the power of flight and remained island-bound. Scientists studying the fossils have confirmed this wasn't just a similar bird doing a similar thing. It was the same lineage, re-evolving nearly the same bird."
"Beyond Aldabra, fossils show other instances of iterative evolution. Certain sea turtles, for example, independently evolved seagrass-munching adaptations multiple times across different epochs. Climate and habitat changes mean that turtles in one area would sporadically go extinct, only for similar adaptations to re-evolve when the habitat changed back. Long, paddle-like limbs. Flat, crushing jaws. Each time the oceans offered up the right environment, evolution"
The Aldabra rail evolved flightlessness after ancestors from Madagascar colonized a predator-free atoll about 136,000 years ago. A catastrophic flood submerged the island and caused the rails' extinction because they could not fly or swim. After seas receded, rails from Madagascar recolonized Aldabra and rapidly re-evolved similar flightless forms from the same lineage. Biologists call this phenomenon iterative evolution, where evolution repeatedly produces similar traits or forms under recurring environmental conditions. Fossils show iterative evolution in other groups, such as sea turtles that repeatedly evolved seagrass-feeding adaptations—paddle-like limbs and flat crushing jaws—whenever habitats favored those traits. Iterative evolution implies predictable evolutionary responses to recurring ecological opportunities.
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