The theories that explain the evolution are hypothetical. There is no practical proof for them. In fact, it is not possible for anybody to observe even a single change in favour of evolution that occurs in the body of organisms as our life span is too short to notice such slow changes. Hence scientists collected evidences from different branches of the biology. we find Some of them are
a. Evidences from palaeontology,
b. Evidences from embryology,
c. Evidences from comparative anatomy
d. Evidences from cell and molecular biology
a) Evidences from Palaeontology: Palaeontology (Gr. Palaios - old, on-existing, logos - to study) is the study of prehistoric life through fossils. Fossils are the remnants of plants or animals that were preserved in the layers of the earth and have been excavated from the soil. They are of various types like moulds, casts, petrifications, traces, coprolites (fossilized faecal matter), actual remains of animals, etc. They support the idea that life has gradually evolved on the earth. The biologists and palaeontologists have found the fossils of many transitional forms (connecting links) which link all the major groups of vertebrates e.g. Eusthenopteron between fishes and amphibians, Seymouria between amphibians and reptiles, Archaeopteryx between reptiles and birds, Cynognathus between the reptiles and themammals etc.
Do you know? The age of a fossil is calculated by using Carbon14,
Uranium238 and Potassium40. Of these, as C14 is commonly used in this
technique, this method is called Radio Carbon Dating method.
A complete fossil record of the various stages in the evolution of horse is available. It indicates that evolution is a gradual process and not a sudden creation of a species.
Geological Time Scale: The earth contains different layers of sediments of which, the bottom layer is the oldest layer and the upper layer is the most recent layer. Based on the age of rocks, a time scale was prepared and it is called the geological time scale, it depicts the different stages of the evolution of life on the earth over the past millions of years. It consists of five Eras
Evidences from embryology: The study of the formation and early development of an organism is called embryology. Ernst Haeckel is considered the 'Father of Embryology' and Von Baer is considered the Father of Modern Embryology. When the embryos of different animals are observed, we find a fundamental similarity which tells us that there is a relationship among the animals. Embryology provides evidences from i) the observations of Von Baer, ii) sequence of the developmental stages of some animals, and iii) the biogenetic law
i) The observations of Von Baer: Von Baer studied the embryology of fish, salamander, tortoise, chick and man. He observed that the early embryos of the above animals resemble each other closely. But these embryos differ in the final stages due to the formation of specialized characters. It indicates that the above animals have a common ancestor.
ii) Sequence of the develop-mental stages: The life of all the multicellular organisms begins with a single celled stage, the zygote. It undergoes cleavages to produce the first stage embryo, the morula, which develops into a single layered
second stage embryo, the bias tula. It develops into the third stage embryo, the gastrula, which finally develops into adult. During this process, the zygote represents the unicellular stage, morula and blastula stages represent the colonial protozoan stages, whereas the gastrula stage represents the cnidarian stage. The development of the embryos of different organisms differs after the gastrula stage. This sequence of embryos shows that every multicellular organism passes through the above stages representing their common ancestry.
