1. Morphological and structural evidences: Comparative study of the morphology and anatomy of organisms indicate that few of the features are similar. These are as follows:

A. Body organization: The body organization of different organism is evolving over time with different level of organization. The unicdellular organism with single cells are the most primitive bdy organization followed by cells to arrange to give rise tissues, the tissues gather to form organs, and organ co-operate to form organ-system. For examples, Amoeba is unicellular, sponge is multicellular but these cells are not organized into the tissue to exhibit cellular level of organization. In coelenterates, cells are organized to form tissue but latter do not form organs. This is a tissue level organization. In platyhelminthes and higher animals, different types of tissues give rise to organ-system level of body organization.

B. Homologous organs: The orans of different species of common descent which look different and perform different functions but has similar structure, similar topographic origin and similar embryonic origin are called as homologous organs. Homology is based on divergent evolution. Few Examples of homologous organs are as follows:

Example 1: Forelimb in vertrbrate animals: The forelimb in man, cheetah, whale and bat are different shapes and perform different functions (Figure 5.2). These are used for grasping object in man, running in cheetah, swimming in whale and flying in bat. In each case, the structure of the form arm has similar plan: upper arm having humerus, followed by radius and ulna, and hand with carpals in the wrist. All vertebrates have basic similarity in the structure of their forelimbs due to their origin from a common ancestral with five digits.   

Figure 5.2 : Forelimb of mammals showing homology.