Evolution is the study which deals with the gradual change of living organisms either at once or in a periodic of time in order to adapt to their environment. There are theories which support the theory of organic evolution, these include:-
1. Evidence from fossil record; Fossil is the remain of plants and animals of past found in the sedimentary rock.
The study of fossil is called PALAENTOLOGY.
The study of rock show that dug deeper in the sedimentary rock are more like primitive form of life and those in upper layer are the modern form of life. This study of fossil show that organism remain fixed, they rather change through come from simple to more complex.
2. Evidence from comparative embryology; Embryology is the study which deals with development of embryo. Comparative embryo show that in certain stage of embryonic development of same group of animal are very similar and distinguishable, indicating that those organisms arose frame the common ancestor. For Example， The embryo of fish ,mammal and birds are similar in earlier embryonic stage ,they all appear fish like because all posses gill shits ,gills two heart chamber and tail are disappear. Ancestor is an individual from the whom one is descended.
3. Evidence from comparative anatomy; Anatomy is the study structure and form of organs in the body of living organism.
The basic structure similarities and different among the group of living organism indicate the closely relationship among them.
Some resemblance among organism assumes that these organisms come from same ancestor and the structural modification is due to the environment and genetically changes. The comparative anatomies provide the evidence for organic evolution though two aspect these;
- Homologous Structure; These are the structure of different organism that have some construction but perform different roles. For Example， Pentactily limb, this structure is found in amphibian, reptile, mammals and bird but it performs different function, and these area Running in horse， Flying in birds and in bat， Digging in mode.
- Analogous structure; These are those structures of different organism that ave different but they perform same. For Example，
a. legs of and legs of rabbit both are use for walking.
b. Wings of butterfly and wings of birds both are use for flying.
4. Evidence from comparative physiology; Physiology is the study of function of an organism. The evidence from comparative physiology that body function resembles from other organism.
For example removal of thyroid gland in tad pole in order to prevent metamorphosis can continue. Due to these functions of thyroid gland from cattle which take place in the body of tadpole indicate that change had occurred.
5. Evidence from Vestigial structure; Vestial structure are those structure present in the organism but reduced in one group and well developed in other group of organism . For example，Appendix in man it is much reduced because has no function but well adapted in rabbit because has an important function. These structure perfumed normal functions in their ancestor but well have been other lost, reduced or much develops.