THEME 2 – La Terre, la vie et l’organisation du vivant / 2B : Biodiversité, résultat et étape de l’évolution Activity 2: Origin of the species – Darwin’s finches English class related work: Charles Darwin - The Theory of Evolution – The Scopes Trial Darwin's finches (also known as the Galápagos finches) are a group of about 15 species bird. They are well known for their remarkable diversity in beak form and function. They are often classified as the subfamily Geospizinae. (use the video called “Evolution by natural selection” in the shared folder of your class, or go to https://www.youtube.com/watch?v=s64Y8sVYfFY ) Watch the video one time, then read the text and answer the questions. 1. Describe the differences seen by Charles Darwin and John Gould regarding the collected birds. 2. Charles Darwin attributed these differences to different food sources available on the various islands. Can you explain why? 3. Why did Darwin conclude the finches must have evolved over time from the original mainland species? 4. Based on these results, can you give a definition of evolution by natural selection? Time to speak! Pick one classmate, and each of you will try to describe one of the following figures to each other. Your description must include the following items: - What kind of figure is it? (table, scheme, genealogic tree, graph…) - What is the main idea developed in the figures? (you can use numbers to describe it for example) Useful vocabulary: Finches (pinsons); beak (bec); slightly (légèrement); claw (griffe); mainland (continent); breeding (reproduction); to suit (pour convenir); p. 1 THEME 2 – La Terre, la vie et l’organisation du vivant / 2B : Biodiversité, résultat et étape de l’évolution The study of finches led to the development of one of the most important scientific theories of all time. In December 1831 a naturalist called Charles Darwin boarded the HMS Beagle, bound on a surveying voyage of South America. While the ship and crew carried out coastline surveys, Darwin was 5 free to explore the islands. In 1835 the Beagle arrived at the Galapagos islands, near Ecuador. What Darwin found there surprised him greatly. As well as giant tortoises and marine iguanas, Darwin collected and preserved a variety of different songbirds called finches. Upon returning to the UK he examined them together with ornithologist John Gould and made some fascinating discoveries. 10 The scientists observed that the birds were all similar to a single type of finch found on mainland South America, suggesting that these mainland finches had originally colonized the islands. However, the Galapagos finches were all slightly different from the original mainland species, and they were also different from each other. The finches on each island showed distinct variations in their overall size, beak shape and claw size. These differences were attributed to the different food sources 15 available on the various islands of the Galapagos. Some of the birds had long thin beaks, and sharp claws suited to catching and eating insects, while others had large powerful beaks suitable for cracking open nuts. Because of the distances between the islands, breeding between different species of finch was unlikely, and Darwin concluded that the finches must have evolved over time from the original mainland species to suit the conditions found on each individual island. In all, 13 of the birds brought 20 back by Darwin were identified as being entirely new species, all similar to each other, but with definite variations from their common ancestor. Darwin proposed that the variations seen both within and between the finch species arose by chance. Variations which gave any individual a competitive advantage made them more likely to survive 25 and therefore reproduce, outcompeting those with less advantageous characteristics. Darwin called this theory Natural Selection and he published it in his book “On the Origin of Species” in 1859. Evolution by natural selection is now widely agreed to be the most accurate theory to explain the origin and diversity of all life on Earth. p. 2 THEME 2 – La Terre, la vie et l’organisation du vivant / 2B : Biodiversité, résultat et étape de l’évolution 1. Describe the differences seen by Charles Darwin and John Gould regarding the collected birds. The Galapagos finches were all slightly different from the original mainland species, and they were also different from each other. The finches on each island showed distinct variations in their overall size, beak shape and claw size. 2. Charles Darwin attributed these differences to different food sources available on the various islands. Can you explain why? Some of the birds had long thin beaks, and sharp claws suited to catching and eating insects, while others had large powerful beaks suitable for cracking open nuts 3. Why did Darwin conclude the finches must have evolved over time from the original mainland species? Because of the distances between the islands, breeding between different species of finch was unlikely. Darwin concluded that the finches must have evolved over time from the original mainland species to suit the conditions found on each individual island. 4. Based on these results, can you give a definition of evolution by natural selection? Variations which give any individual a competitive advantage make them more likely to survive and therefore reproduce, outcompeting those with less advantageous characteristics. Darwin called this theory Natural Selection p. 3 .