The opening paragraphs will provide quick answers to questions related to the topic of a bird evolving back into existence. The most notable example of this phenomenon is the case of the Aldabra rail on the Aldabra Atoll in the Indian Ocean. Here are some key facts:
Quick Answers
What bird evolved back into existence? The Aldabra rail evolved back into existence on the Aldabra Atoll after going extinct there over 100,000 years ago.
When did it go extinct originally? The Aldabra rail originally went extinct on Aldabra Atoll around 136,000 years ago.
How did it evolve back? After going extinct, some members of the species survived on nearby islands. Over 100,000 years later, the rails were able to make their way back to Aldabra and evolve back into existence in that habitat.
Why is this significant? This is considered one of the only documented cases of iterative evolution, where a species goes extinct in a habitat but is later able to evolve back and reoccupy that ecological niche through natural processes.
The Extinction of the Aldabra Rail
The Aldabra rail (Dryolimnas cuvieri aldabranus) is a flightless bird in the rail family that is endemic to the Aldabra Atoll in the Indian Ocean. Aldabra is part of the Seychelles island chain and is over 200 miles from the nearest major island. This remote location made Aldabra home to many unique species, including the Aldabra rail.
The Aldabra rail evolved on Aldabra Atoll over 300,000 years ago, losing its ability to fly due to lack of predators. Around 136,000 years ago, the rail went extinct on Aldabra during a major extinction event that wiped out much of the atoll’s unique fauna. Rising sea levels likely inundated the island, destroying the rail’s mangrove habitat. With no ability to fly away or disperse to other islands, the flightless rail was wiped out.
However, a related subspecies of rail (Dryolimnas cuvieri abbotti) survived on nearby islands in the Seychelles. This flightless bird was closely related to the original Aldabra rail but was genetically distinct enough to be classified as a separate subspecies. The Aldabra rail was gone from its namesake home, but it lived on elsewhere in a different form.
Recolonization of Aldabra
Over 100,000 years passed before the rail was able to make its return to Aldabra Atoll. As sea levels fluctuated again, the island became habitable once more. The surviving Abbey’s rails on nearby islands were eventually able to cross the ocean channels and recolonize Aldabra.
Once back on Aldabra, the rail found its ideal habitat again – the mangrove swamps and dense vegetation that had been wiped out during the previous extinction. With plentiful food and habitat, the rail was able to establish a population and thrive. Over many generations, the rail evolved and adapted back into the original form that inhabited Aldabra over 100,000 years earlier.
This process was made possible by the rails’ close genetic links to the original Aldabra subspecies. Although Abbey’s rail had diverged on the nearby islands, it retained the genetic components needed to re-adapt to the Aldabra ecosystem when given the chance. The end result was an essentially identical bird filling the same ecological role, although the modern Aldabra rail developed completely naturally from the returning population.
Evidence of Iterative Evolution
The re-evolution of the Aldabra rail on Aldabra Atoll provides one of the few concrete examples of iterative evolution. This phenomenon is when a species re-appears after going extinct by re-emerging from a closely related population through natural processes.
There are several key lines of evidence that demonstrate this iterative evolution in the rails:
- Fossil evidence shows that a morphologically distinct rail species inhabited Aldabra over 100,000 years ago before going extinct.
- Genetic analysis proves that the modern Aldabra rail is highly similar to the extinct species despite evolving in isolation for thousands of generations.
- Abbey’s rail was shown to be the closest living relative of the original Aldabra rail, providing a source population for recolonization.
- No human intervention or intentional re-introduction took place, showing that natural dispersal led to the rails’ return.
Together, these facts support the conclusion that the old Aldabra rail did indeed evolve back into existence naturally. This is considered one of the most compelling cases of iterative evolution in the wild.
Why Is This Significant?
The re-emergence of the Aldabra rail is considered scientifically important for several reasons:
- It demonstrates that extinction is not always forever. Under the right circumstances, some species can re-evolve if they still exist in related forms elsewhere.
- It shows that ecological niches can remain open for thousands of generations, waiting to be filled again.
- It provides evidence that evolution can repeat itself, recreating complex forms that were lost.
- It expands the view of evolutionary processes and shows that extinction and re-emergence can be part of some species’ natural history.
Overall, the rails represent a fascinating real-world example of presumed-extinct species being able to reclaim lost niches through natural processes. It provides hope that human-caused extinctions may not always be permanent losses, if related populations and habitats can be preserved.
Other Examples of Iterative Evolution
There are a few other potential examples of iterative evolution that show this phenomenon is not limited to just the Aldabra rail:
- Bulmer’s fruit bat – A giant fruit bat once lived on New Guinea but went extinct around 10,000 years ago. Today, a very similar species has evolved there with no clear ancestral population, suggesting iterative evolution.
- Strombid gastropods – Extinct shell-bearing snails called strombids re-appeared in fossil records after a long absence. Genetic data shows the modern forms were naturally re-derived from other strombid lineages.
- Caribbean lizards – Two lizard species thought to have gone extinct a million years ago have apparently re-emerged in the Caribbean in close equivalents of their original forms.
These examples hint that iterative evolution may happen more often than realized. Many ancestral links have likely been obscured by lack of genetic evidence in older extinct species. Future research may uncover more instances of presumed-extinct species naturally returning from evolutionary side branches.
Conclusion
The Aldabra rail represents one of the clearest and most scientifically accepted cases of a species re-evolving after extinction. Its ability to reclaim its ecological niche after over 100,000 years exemplifies the resilience of natural evolutionary processes. Even when species disappear in a region, they can still re-emerge if they survive in other forms and habitats. This rare phenomenon demonstrates that presumed-extinct species may still persist and rebuild themselves through natural selection.