define evolution how does it occur ?describe how fossils provide us evidences in support of evolution
Answers
The gradual process of change in the heritable traits of populations over millions of years leading to the formation of new species is known as evolution. According to Darwin's theory of evolution, natural selection is responsible for the formation of new species over the course of time. The organisms which are best adapted to survive in the given environmental conditions are selected by nature and they reproduce. The variations that exist in these individuals are passed to next generation while the individuals with unfavourable variations perish. But the exact cause of these variations is a mutation which leads to speciation.
Fossils are the remnants of the past organisms which get buried in sedimentary rocks. Different fossils are formed in the different aged rock sediments. The study of fossils existing in the different rock layers indicate the time period when they existed. Thus different life forms have been formed at different times in the history of the earth. Fossils indicate how the evolution took place leading to the formation of complex life forms from simple ones by the gradual process. For example, fossil bird Archaeopteryx is considered as a connecting link between reptiles and birds indicating that birds evolved from reptiles. It shows the presence of characters of both birds and reptiles like the presence of teeth, wing feathers, clawed toes and tail.
The slow change in the body design of an organism over a long period of time is termed as evolution. It helps an organism to survive in its surroundings.
Evidences of Evolution
Fossils − They represent plants and animals that lived millions of years ago and are now extinct. Different aged rock sediments contain fossils of different life-forms, which probably died during the formation of the particular sediment.
Comparative anatomy and morphology − It shows evidences of the similarities and differences between living forms of today and that of the prehistoric times. Some of the examples of comparative anatomy and morphology are:
Homologous organs − All mammals share the same pattern of forelimbs. Though they perform different functions, they are anatomically similar. This is called divergent evolution and the structures are called homologous structures (common ancestors).
Analogous organs − The pair of organs is not anatomically similar, but performs the same function (e.g., the wings of butterflies and birds). This is called convergent evolution .