Tortoises have a classic example of a mutualism symbiotic relationship with some species of Galapagos finch.
Darwin proposed that the Galapagos finches evolved on the islands from a single species of finch from mainland South America.
In fact, the opposite may be happening, as several species of Galapagos finches now appear to be merging through hybridization.
The Islands were also home to Darwin's most famous specimens, the Galapagos finches, a number of which he shot and kept for further study.
The great evolutionary plasticity of bill form and function is well known from the radiations of Hawaiian honeycreepers and Galapagos finches.
Whilst studying wildlife on the Galapagos Islands he noticed that the Galapagos finches showed wide variations - eg in beak shape and size - from island to island.
Darwin's study of characteristics of species on isolated islands such as these Galapagos finches, and of fossil animals, led him to conclude that evolution had occurred.
The Galapagos finches remain a marvelous example of the principle of adaptive radiation.
All of the Galapagos finches are distinct from those on the mainland, yet they are similar enough to suggest that they arose from a common ancestor on the South American mainland.
The different species of Galapagos finches show no differences in clutch size, incubation time, nesting time, or shape of the nest.
Furthermore, he displays his ignorance of the creationist position when he implies that creationists don't think all the Galapagos finches have a common ancestor.
The Galapagos finches were considered an extreme case of quick evolution caused by an extreme environment.
It is Darwin's study of the 14 species of Galapagos finch that gave him the evidence he used for his thesis that ‘species were not immutable’, an idea that he developed for more than 20 years before publishing his famous On the Origin of the Species by Means of Natural Selection.
Our common drives are as much the product of evolutionary processes as are the physical characteristics of Galapagos finches.
An interesting note about the tortoise concerns the Galapagos finch.
Researchers not too long ago successfully bred the offspring of two ‘species’ of Galapagos finches.
And there is even a Galapagos finch which, like a vampire bat, laps up the blood of its victims (often seabirds in this case) after piercing their skin or feather shafts.
A Galapagos finch that helped reveal the origins of species to Charles Darwin has now undergone a spurt of rapid climate-driven evolution, biologists report.
By comparison with the Galapagos finches, the evolutionary response of the single species of Darwin's finch on the humid, tropical Cocos Island is much less imposing.
The family includes 281 species altogether, out of them 13 are Galapagos finches or ‘Darwin finches’ which are the most famous birds in science.