An accidental laboratory
Tristan da Cunha is the most remote inhabited archipelago on Earth. The main island sits in the South Atlantic, approximately 2,800 kilometers from South Africa and 2,400 kilometers from the nearest inhabited land, Saint Helena. This deep isolation makes the island group a natural laboratory for studying evolution. The volcanic islands, which began forming as recently as one million years ago, have been colonized by species that managed to cross vast stretches of ocean. Over time, and without competition from mainland predators, these colonizers adapted to their new environment, resulting in a unique collection of life.
The resident is the Inaccessible Island Rail (Laterallus rogersi), the world's smallest living flightless bird. Found only on the aptly named Inaccessible Island, this tiny bird measures just 13 to 15.5 centimeters long and weighs between 34 and 49 grams. DNA analysis shows its ancestors arrived from South America around 1.5 million years ago. With no land predators to escape from, the ability to fly became unnecessary, and the species evolved into its current flightless form. The archipelago has several endemic finches, or buntings, which have diversified in a manner similar to Darwin's finches. Wilkins's Bunting (Nesospiza wilkinsi) developed a large, robust bill for cracking the hard fruits of the Phylica trees, while the Nightingale Bunting (Nesospiza questi) has a smaller bill suited for seeds and invertebrates.