Evolution and Charles Darwin

Evolution and Charles Darwin By Andrew and Reece Introduction Charles Darwin’s theory of evolution explains how species of living things have changed over time. The theory is supported by evidence from fossils, and rapid changes that can be seen to occur in microorganisms such as antibiotic-resistant bacteria. Many species have become extinct in the past, while the extinction of species continues today. How did Life start? • It is not possible to be certain how life on Earth began because: • The Earth is about 4,500 million years old • There is evidence living things existed on Earth at least 3,500 million years ago • No-one was there to record how life began Charles Darwin • Charles Darwin was an English naturalist who studied variation in plants and animals during a fiveyear voyage around the world in the 19th century. He explained his ideas on evolution in a book called On the Origin of Species, published in 1859. • Darwin’s ideas caused a lot of controversy, and this continues today, because they can be seen as conflicting with religious views about the creation of the world and creatures in it. The Finches Darwin studied the wildlife of the Galápagos Islands - a group of islands on the equator almost 1,000km west of Ecuador. He noticed that the finches (songbirds) on the different islands were fundamentally similar to each other, but showed wide variations in size, beaks and claws from island to island. For example, their beaks were different depending on the local food source. Darwin concluded that, because the islands are so distant from the mainland, the finches which had arrived there in the past had changed over time. Darwin’s theory of evolution The basic idea behind the theory of evolution is that all the different species have evolved from simple life forms. These simple life forms first developed more than three billion years ago - the Earth is about 4.5 billion years old. The timeline below shows some of the key events in the evolution of life on Earth, from the first bacteria to the first modern humans. Natural Selection Individuals in a species show a wide range of variation is because of differences in their genes individuals with characteristics most suited to the environment are more likely to survive and reproduce the genes that allow these individuals to be successful are passed to their offspring Origins of life Some people find it hard to accept that such complexity could have evolved through natural selection. Some religious people believe all living things on Earth were made by God, or that life was begun by God but then evolved through natural selection. We will probably never be absolutely certain about how life began - as no-one was there to observe it. But scientists must base their theories upon evidence. Lamarck • Darwin was not the only person to develop a theory of evolution. Jean-Baptiste Lamarck was a French scientist who developed an alternative theory at the beginning of the 19th century. His theory involved two ideas: • the law of use and disuse • the law of inheritance of acquired characteristics Comparisons • Comparison of Lamark's and Darwin's theories • Lamarck • a giraffe stretches its neck to reach food high up • the giraffe's neck gets longer because its used a lot • the giraffe's offspring inherit its long neck • Darwin • a giraffe's with a longer neck can reach food high up • a giraffe is more likely to get enough food to survive to reproduce • a giraffe's offspring inherit its long neck Fossils • Most of the evidence for evolution comes from the fossil record. Fossils show how much, or how little, organisms have changed over time. • One of the problems with the fossil record is that it contains gaps. Not all organisms fossilise well. And many fossils are destroyed by the movements of the Earth, or have simply not been discovered. Rapid changes Evolution is difficult to observe because it usually occurs over many years. This is one reason why the theory of evolution is still a theory, not a law. Since no-one was around millions of years ago to make observations, take notes or carry out experiments, evolution cannot be proved in the usual scientific sense. However, rapid changes in species have been observed that support the theory. Peppered moths Before the Industrial Revolution in Britain, most peppered moths were of the pale variety. They were camouflaged against the pale birch trees they rested on. Moths with a mutant black colouring were spotted easily by birds and eaten. This gave the white variety an advantage, making them more likely to survive and reproduce. • Airborne pollution in industrial areas blackened the birch tree bark with soot. This meant the mutant black moths were now camouflaged, while the white variety became more vulnerable to predators. It gave the black variety an advantage. They were then more likely to survive and reproduce. Over time, the black peppered moths became far more numerous in urban areas than the pale variety. Extinction Individuals that are poorly adapted to their environment are less likely to survive and reproduce than those which are well adapted. Similarly, it is possible that a species which is poorly adapted to its environment will become extinct. • Here are some factors that can cause a species to become extinct: • changes to the environment, such as the climate • new diseases • new predators • new competitors The dodo The dodo was a large flightless bird that lived in the Mauritius, a group of islands in the Indian Ocean. These were uninhabited, and the dodo had no natural predators. Then Mauritius were colonised by the Dutch in 1638. Dodos were hunted for food and easy to catch, because they were not afraid of people. New competitors were brought to the islands, including pigs, cats and rats, which ate the dodos' eggs and young. Within 80 years, the dodo was extinct. Fin By Andrew Bartholomew and Reece Dimech 11D