Evolution by Natural Selection

In 1831, at the age of just 22, Charles Darwin was hired as the naturalist on board HMS Beagle as it set off on a five-year voyage to create maps of new territories for the British Admiralty. One of these unchartered regions was the Galapagos, an isolated group of volcanic islands in the Pacific. It was here that Darwin made observations and collected specimens that he later acknowledged as an inspiration for his ideas on evolution by natural selection and the origin of new species.

Charles Darwin and his insights from the Galapagos are so important they have even made it onto the GCSE biology syllabus! But contrary to what the textbooks would have our students believe, Darwin wrote almost nothing about the Galapagos finches, describing them as “an inexplicable confusion”. But it was the work of evolutionary biologists that followed, notably Peter and Rosemary Grant, that established the radiation of Galapagos finches – also referred to collectively as “Darwin’s finches” – as a perfect illustration of the origin of new species. In a lunchtime talk, biology teacher Dr Henry Nicholls described how changes in the environment – like a drought, for instance – can lead to the death of certain individuals in a population, with the survivors passing on the particular traits that helped them get through the tough times – like larger bills – to their offspring. Through this process of natural selection, species change. This is how biologists think that a single colonising population of finches blown off course to Galapagos around 3 million years ago has since radiated into 14 different species, some feeding on seeds, some on cactuses, some on insects, and some – the sharp-beaked or vampire finch – on the blood from open wounds of other birds.

The same pattern of a rare colonisation event, followed by divergence and speciation, is now a familiar story across the Galapagos archipelago, explaining why there are 14 species of giant tortoise, 15 species of Scalesia, several different Opuntia cacti, more than 10 species of flightless weevil and over 70 species of land snails, each adapted to occupy its own unique microhabitat.

The students worked in pairs to collect answers to key questions from the talk. Those with the highest scores walked away with a penguin biscuit, a nod to the Galapagos penguin, the world’s smallest penguin species and the only one to stray into waters north of the equator.