The theory of evolution suggests that the first living things on the Earth appeared over 3000 million years ago and were very simple single celled creatures. Slowly, over millions of years, these simple creatures evolved into the many thousands of plants and animals that we see today. Much of the evidence for this theory has come from studying fossils, the remains of plants and animals that lived many years ago. These fossils were formed when the plants or animal died and were buried in a layer of mud. Over millions of years this became sedimentary rock. From studying fossils, scientists are able to determine when the plant or animal was actually alive and are able to build up a picture of the changes that they have undergone over time. Charles Darwin is noted for carrying out much work in the area of evolution. In his book ‘The Origin of Species’ he outlined a theory that he called natural selection. This theory contains three main ideas:
- variation within a species: within the same species there are many different individuals. The species of which humans are a part highlights this as we notice differences between people, such as height, weight, hair and skin colour. These differences occur for both genetic and environmental reasons.
- survival of the fittest: because of the variations within species, there is often a struggle amongst plants and animals for survival. Those that do survive are usually those that are the fittest, less likely to suffer diseases, able to avoid predators, able to compete successfully for resources such as space, shelter and food and able to adapt to differing climates. Those plants and animals that are able to survive are able to pass the ‘survival characteristics’ on to their offspring. This becomes a process called natural selection and leads to species developing and evolving in a particular way.
- adaptation of organisms: the changes that take place within a species to allow it to survive are called adaptations and result from those individuals with the appropriate characteristics being more likely, and able, to reproduce.
