What is natural selection An important question Why do the animals plants and people on our planet look and act the way they do And why are there so many different types or species of living things These are among the most important questions in science especially biology the science of life For most scientists the answer is natural selection Discovering the world The theory of natural selection developed in the 1800s This was a time when scientists and explorers were finding out more and more about the natural world and its plants animals and other creatures such as fungi and bacteria From fossils they also learned about the creatures that lived on the earth a long time ago They wondered why some of these such as dinosaurs were so different from modern life-forms Had living things been changing or evolving all this time And if they had how Finding an answer Several scientists came up with interesting ideas but the most famous of them all was Charles Darwin and the This artwork shows the giant Megalodon shark the biggest fish ever The shark lived between 25 and 1 6 million years ago and fossils show it was 66 feet 20 m long A modern white shark also shown measures around 20 feet 6 m
The camel has evolved to become adapted to desert life and can survive for many days without food or water It can also withstand the extreme temperatures in the desert and its wide feet help it walk on soft sand theory he named natural selection Today Darwin’s work is seen as one of the most important scientific discoveries ever made However not everyone agrees with everything Darwin said and his theory still causes arguments I have called this principle by which each slight variation if useful is preserved by the term of Natural Selection Charles Darwin from On the Origin of Species published 1859 How natural selection works So what is this theory It will be explained again later but here is a simple version In any species some individuals will be better at surviving than others For example some rabbits can run faster than others and are better at escaping from predators Those that survive longest will be more likely to have plenty of young They pass on their qualities such as big strong back legs to their young In this way nature selects the most useful qualities in a species Over a long time as this happens over and over again the species changes or evolves What is evolution Evolution is a word that means gradual change in a series of stages By the 1800s most scientists agreed that living things must have evolved over time Natural selection is not the same thing as evolution but it is a way of explaining how evolution happens 7
Early ideas Ancient thinkers and evolution Several ancient thinkers wondered why there were so many living things and why judging by the fossils they found life seemed to be so different from long ago Some of their ideas came remarkably close to what we now believe is the truth Out of the mud Anaximander an ancient Greek who lived more than 2,500 years ago decided that living things had developed from sea mud He also said that humans didn’t exist at first but developed from fish Like many Greeks Anaximander did not have much evidence for his ideas However this was one of the first attempts to explain evolution Dying out Another great Greek Empedocles and the later Roman writer Lucretius suggested that some creatures that had once been alive were poor at surviving or not useful and had died out This early theory is similar to Darwin’s ideas on natural selection The changing earth Some early scientists saw that the earth had changed over time Anaximander’s student Xenophanes found seashell fossils in rocks on dry land and realized Empedocles Date of birth c 495 B C Place of birth Probably Sicily Greatest achievements Although most of his work has long since been lost traditionally he was famous for two long poems The first On Nature was about how all living things were created from four elements earth air fire and water Purifications the second poem was concerned with religion Interesting fact Scholars today think the two poems may actually have been one long one Date of death c 435 B C 8
THAT’S A FACT Many ancient stories about how the earth and all living things came into being tell of a time when there was nothing but water Today many scientists believe that all life first evolved in water that this land had once been covered by sea Around the year A D 1,000 Chinese scientist Shen Kuo and Persian thinker Ibn Sina both came up with the idea that rocks moving and changing over time were responsible for the shape of the land on earth Fossils like these of fish convinced scientists in the ancient world that the earth must have changed over time They realized that rocks now found on land must have once been under the sea These ideas later became very important to the theory of natural selection as they showed that the world was very old and there had been plenty of time for living things to evolve Breakthrough These earliest ideas about evolution challenged long-held traditional beliefs about how life on earth was created They may not have been exactly right but they paved the way for later scientists 9
