On the News | Galápagos giant tortoises show that in evolution, slow and steady gets you places @ The Guardian

On the News @ The Guardian

Title: Galápagos giant tortoises show that in evolution, slow and steady gets you places


“As I was walking along I met two large tortoises, each of which must have weighed at least two hundred pounds: one was eating a piece of cactus, and as I approached, it stared at me and slowly stalked away; the other gave a deep hiss, and drew in its head. These huge reptiles, surrounded by the black lava, the leafless shrubs, and large cacti, seemed to my fancy like some antediluvian animals. The few dull-coloured birds cared no more for me, than they did for the great tortoises.”

A drawing of Testudo abingdonii (now Chelonoidis abingdonii) from Darwin’s 1890’s book on his Beagle adventure. Illustration: C. Darwin, 1890. (@source)

On a hot September day in 1835, Charles Darwin met his first giant tortoise on Chatham Island, part of the Galápagos archipelago. After visiting other islands in the archipelago, he came to realize that each island had its own, but slightly different giant tortoise. This was already known by the natives, who could distinguish the tortoises from different islands, but Darwin was struck with wonder (he even brought some tortoises back to Europe as pets). Eventually, his wonder forever changed our understanding of the natural world.

The Galápagos giant tortoise species complex (Chelonoidis nigra) forms an example of an adaptive radiation; a rapid diversification of a lineage when a new food source or ecological niche becomes available. The first giant tortoises are thought to have reached the islands two to three million years ago from South America (Caccone et al., 2002), and subsequently spread through the archipelago as new land emerged from the volcanic sea floor. At one point there were 15 different species (or subspecies, this is a matter of discussion, see Poulakakis et al., 2015). Three of them are now extinct, and scientists are struggling to save the remaining ones. (…)” READ MORE

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