i. Palaeontological evidence of evolution.
a. Fossils are defined as the dead remains of plants and animals that lived in the past in various geological layers.
b. Unlike the evidences from other branches of biology, evidence from fossils are sound, direct and reliable.
c. Fossils are described as the true witnesses or documents of evolution.
d. The development in the field of Geology reveals that the primitive forms of organisms occupy the lower layers and the advanced forms occupy the upper layers of the earth during fossilization.
e. Fossils are found in sedimentary rocks, amber, volcanic gas, ice, peat bogs and soil, etc.
ii. Anatomical evidences of evolution:
The study of internal structure of an organism is called anatomy.
a. Anatomical evidences are of three types, viz. Homologous organs, Analogous organs and Vestigial organs.
b. Though the animals belonging to different groups vary greatly in their external morphology, yet they show the same structural plan internally, i.e. in their anatomy.
c. The organs having common origin but performing different functions are known as homologous organs and the phenomenon is called homology.
Homology is the result of divergent evolution.
Homology of organs indicate their common ancestry. e.g. forelimbs of whales, bat, birds, amphibians and humans as all have basic anatomical structure with bones humerus, radius – ulna, carpals, meta – carpals and phalanges.
1. Analogous organs
i. The organs having different origin but performing same function are called analogous organs and the phenomenon is called analogy. e.g. wings of butterfly (insects) and birds.
ii. Analogy is the result of convergent evolution.
2. Vestigial organs
Organs are functionless and rudimentary to the possessor but were functional in the ancestors and are also functional in related animals. e.g.
i. Caecum and vermiform appendix
ii. Nictitating membrane
iii. Coccyx or tail vertebrae
