The theory of evolution suggests that there is a change in inherited traits of a population of organisms through generations. This theory gathers more evidence with the study of fossils of prehistoric organisms. The word fossil is derived from the Latin word ‘fossus’, which literally means ‘having been dug up’. Fossils are the preserved remains of animals, plants and other organisms found in the sedimentary layers of rocks.
One of the most widely used and accepted techniques to determine the actual or relative age of the earth's crust, fossils and ancient artefacts is radioactive dating. Fossils are also are of great help in morphological and anatomical studies. They also help in comparative anatomy. There are two concepts of comparative anatomy—homologous and analogous structures. If we look at mammals such as human beings, cats, whales and bats, we find that all of them have similar patterns of bones in their forelimbs. These structures point to a common ancestry and this type of evolution is called divergent evolution. On the other hand, when anatomically different structures evolve to perform similar functions in different organisms, they are known analogous structures.
Natural selection of the fittest organisms has been crucial to the process of evolution. In a collection of moths in the 1850s, before the onset of the Industrial Revolution in England, a larger number of white-winged moths were detected than dark-winged moths. Conversely, after industrialisation, it was observed that the population of dark-winged moths had increased considerably in the same area. The reason cited for this reverse proportion of moths was that before industrialisation, the barks of trees were covered with white lichen which camouflaged the white-winged moth and exposed the dark-winged moth to predators. After industrialisation, however, the lichen died due to pollution and the barks of the trees became black due to smoke and soot. This created perfect conditions for the growth of dark-winged moths as they could not be spotted easily on the dark surfaces now. Meanwhile, the white-winged moths could be easily noticed by predators and as a result, their number shrunk.
Evolution is also impacted by processes and materials derived from human activities. Excessive use of pesticides results in a selection of resistant varieties within a small period of time. Therefore we conclude that evolution is not a predetermined process but a random process. It is completely based on chance events, chance mutations and it is also impacted by human activities.