A Fossil comes from an organism (living thing) that survived long ago. After the organism died, parts of it were buried in sand or mud, preserved in the rocks and turned to solid stone. Hard, tough body parts form the best fossils because they do not rot away quickly after death and so have more chance of being preserved. They include animal bones, teeth, horns, claws and shells, and plant wood, bark and cones.
Fossils show that many kinds of animals, plants and other organisms have lived during the hundreds of millions of years that make up the Earth’s past. Most of these organisms, such as ammonites, trilobites, dinosaurs and mammoths, are no longer alive. Other types have survived almost unchanged for millions of years. Sharks and turtles are examples of these. Some have appeared quite recently, such as human beings. The study of fossils, known as palaeontology, is one part of the evidence for evolution—the way that living things change through time.
Why does evolution happen? Why don’t living things simply stay the same? Life is a continual struggle to avoid predators and bad weather, to find food and shelter, and to breed. Living things that survive the struggle are those best suited or adapted to the conditions. However the conditions change naturally with time. Some kinds of food may become more scarce. The climate may become colder or warmer. New diseases may appear. Living things must evolve to suit new conditions or die out.
Besides studying fossils, we can see evolution at work by observing living things today. Some types of animals are very similar to each other. Hawaiian finches for example, differ only in small ways. They probably all evolved from one original species. Their beaks changed, or adapted, to eat different foods.
EVIDENCE FOR EVOLUTION
An embryo is a living thing at an early stage of its development, like a human baby during the first few weeks of life growing in its mother’s womb. At this early stage, a developing human embryo looks very similar to the embryo of any other mammal, such as a monkey or cow. It is also similar to the embryo of a bird, a reptile like a turtle, and even a fish. The simplest explanation as to why these very young organisms are so similar to each other is evolution. Over millions of years they have evolved from the same ancestors. They are now different as adults. But they have kept the similarities to their ancestors, and so to each other, during the early stages of their development.
NATURAL SELECTION
Evolution happens by the process of natural selection. In the struggle for survival, some living things adapt better to the conditions. These individuals are more likely to survive and produce offspring. If the offspring inherit the same features, they too have more chance of survival. It is as if nature chooses who will survive and who will not.
Evolution by natural selection explains the bodily features and behaviours of living things—even those that seem to be a hindrance. The long, colourful feathers of a male bird of paradise may seem a drawback. They make him more obvious to predators and less able to escape from them. But they also attract females for breeding, and so this feature is passed on to his offspring.
Picture Credit : Google