Explain embryological evidences to support the organic evolution.

Explanation

Embryological Evidences (Evidences from Embryology). The evidence are based on the comparative study of tri. embryos of various animals.
(a) Similarity in Early Development. In all the multicellular animals the fertilized egg (Zygote) undergoes segmentation (cleavage) to produce a solid structure, the mornla, which devclops into a single layered hollow blastula. This changes into either two or thrce layered gastrula. The animals haying two layered gastrula arc said to be diploblastic, e.g., coelenterates. The animals in which, three layered gastrula is found are known as triploblastic, such as frog. Such a similar early development establishes a close relationship among all multicellular animals.
(b) Development of Vertebrate Organs. Development of many vertebrate organs (e.g., heart, brain, kidney) indicate the possible path of evolution well as the common ancestry of vertebrates. For example, during its development the heart of a mammal or bird is initially two-chambered (as in fishes), then three chambered (as in amphibians and some reptiles) and ultimately four chambered. It clearly shows that birds and mammals have originated from fishes through amphibians and reptiles.
(c ) Recapitulation Theory/Biogenetic Law. In 1828, Von Baer, the father of modern embryology, proposed Baer.s law. It stated that during embryonic development, the generalised features (such as brain, spinal cord, axial skeleton, aortic arches etc. that are common to all vertebrates) appeared earlier than the special fcaturos (like hair in mammals only, features in birds only, limbs found in quadrupeds only), which distinguish the various members of the group. Later on, this law was modificd as the biogenetic law by Ernst Hacckcl in 1866 which states that -"Ontogeny repeats phytogeny". In other words an organism repeats its ancestral history during its development.
Example. In the development of the frog a fish like tailed larva (tadpole) is formed, which swims with the tail and respires by the gills. This indicates that the frog has been evolved frojn-a fish like ancestor.