53. How does palaeontological evidence support the theory of organic evolution ? Explain with an example.

According to the theory of organic evolution several billion year ago very simple, single celled organisms appeared on the earth. They reproduced themselves, each new generation the same as the preceding, except that in some of the new individuals random or chance heritable changes called ‘mutations’ occurred. Most of the mutations were not good enough and the individuals having them died out, but a very few of the mutations conferred some of advantages on the individuals possessing them. These individuals were better adopted to their environment and so were able to reproduce more of their kind. Thus individuals having the advantageous mutations gradually became more in number. According to the theory, by this stepwise process of mutation and natural selection the few original simple life forms were able to change to more complex kinds, better adapted to their environments, to change in the environments or to other environments nearby.

The concept of organic evolution holds that all the varied kinds of plants and animals which are now known, have developed out of earlier types by completely natural, gradual but continuous changes during the passage of time. The study of fossils had added immensely in our understanding of the lines of evolution of many invertebrates and vertebrates. From the fossil records, it may be concluded that evolution has taken place from simple to complex in a gradual way of increasing order. To clear or confirm the concept, the example is—the phylogeny of horse starts with Eohippus which lived in Eocene and was of the size of a fox having longer head. Its legs were short with four toes on each front-foot and three on each hind-foot. The third digit was somewhat longer than the others. All the toes were placed on the ground and used in walking. It was a forest dweller feeding on soft vegetation. 

Thus the fossil records clearly provide the most direct indication of evolution and suggest that through years the early types became more and more complex. It means that the simpler forms gave rise to more complex ones.