Biology: Evolution
evolution noun [U]
the way in which living things change and develop over time; Darwin’s theory of evolution
1 SPEAKING What do you know about evolution? In pairs, share your knowledge.
2 Read the text quickly. What new pieces of information did you learn?
In 1831, an Englishman called Charles Darwin on a scientific expedition around the world, aboard the ship HMS Beagle. Darwin’s job was to notice and collect animals, plants and rocks from the many places they visited. During the trip, he made a lot of discoveries. For example, on the Galápagos Islands, he noticed that birds that ate different types of food had beaks that were different shapes. Darwin also found fossils of extinct animals and noticed that animals from a very long time ago looked different. After five years of travelling, he returned to England. At home, he studied his notes and developed his theory of evolution.
Natural selection (‘The survival of the fittest’)
According to Darwin’s theory, evolution happens through ‘natural ’. This is the process by which only the organisms with that are right for their environment . These organisms then give these successful characteristics to their . This process is sometimes referred to as ‘the survival of the fittest’ and is explained below.
Variation
The members of a single species may appear quite similar but in fact, they are different from each other in very many ways. For example, some are slightly bigger than others, or brighter in colour. Others are slightly healthier or able to move more quickly. (Differences like these – called – are caused by changes that happen when cells divide.) When organisms reproduce, they give their DNA to their offspring. A lot of characteristics, such as colour, size, etc., are contained in this DNA so the offspring get these differences from their parents.
Selection
Each generation has too many offspring. There isn’t enough food for all the offspring so some of them die. Others have helpful characteristics which allow them to stay alive and reproduce. For example, they may be able to run faster and escape from animals that want to kill them, or they might have particularly bright feathers which attract the opposite sex.
Time and adaptation
Helpful characteristics that allow organisms to stay alive are often called adaptations. Organisms with helpful are more likely to live long enough to reproduce. This means that their offspring are more likely to have the adaptation too. Over time – and this could be days or millions of years – the adaptation becomes normal in the species and the species changes (or ‘evolves’). The result is a version of the species that is right for the environment that they live in.
Darwin’s theory of evolution was not accepted by everyone. As part of his theory, he suggested that humans and shared ancestors. This went against the belief that most people had at the time that God created all people and animals.
3 Read the text again. Mark the statements True or False.
4 SPEAKING Can you think of any adaptations which have allowed animals to survive in particular environments?
