Closely related organisms show similarity in morphological characters. Organisms having similar morphology are supposed to be evolved from a common ancestor. Eg; the morphological similarity between human and ave indicates their evolution from a common ancestor. Similarly, Jackal, fox, the wolf may have been evolved from the same ancestor.
Organs which are similar in structure and origin but may different in appearance and function. They support divergent evolution. These organs may have been developed because of sharing of a different environment. Eg;
fig: Homologous organs
Organs which are similar in appearance and function but different in structure and origin is analogous organ. They support convergent evolution. These organs may have been developed due to sharing of a similar environment. Eg;
- Wing of insects and birds
- Fin of fish and flippers of whale
- Trachea of insect and vertebrates
- Sting of honeybee and scorpion
- Sting of Asparagus and leaf of plant
fig: Analogous organ
These are reduced and functionless organs which are supposed to be well developed and functional in ancestors due to environmental change and different mode of life, they become reduced and functionless. Eg;
- Coccyx bone in human
- Vermiform appendix in human
- Body hair in human
- Wisdom teeth in human
- Nictitating membrane in eyes of human
- Ear muscle of human
- Wings of flightless bird
- Pelvic girdle of python
- Splint bones of horse
fig: Vestigial organ
It is the sudden reappearance of ancestral characters in some individuals. Eg;
- Newly born baby with short tail
- Newly born baby with dense body hair
- Projecting canine teeth
- Power of moving pinna
Evidence from connecting link(Euglena)/missing link (Archeopteryx)
Living organisms having the characters of two different group of organisms are called connecting link. They indicate the evolution of one group of organisms from another. Eg;
- Euglena (plants and animals)
- Proterospongea (Protozoa and Porifera)
- Peripatus (Annelida and Arthropoda)
- Neoplina (Annelida and Mollusca)
- Balanoglosus (Non-Chordata and Chordata)
- Protopterus(Fish and Amphibia)
- Sphenodon (Amphibia and Reptilia)
- Echidna, Ornithorhynchus (Reptiles and Mammals)
Extinct organisms having the characters of two different group of organisms are called missing link. Eg;
Archeopteryx (lizard bird of Jurassic period)_______: missing link between reptiles and bird
- It had a beak like in birds but contains teeth.
- It had wings like birds but contain claws.
- It had feathers like birds but contains scale like reptiles.
- It has tail feathers like in birds but contains tail vertebrae like in reptiles.
These characters of Archeopteryxjustify that birds were evolved from reptiles. Reptiles are supposed to be the ugliest creatures, but birds are beautiful and glorious. So, birds are called glorified reptiles.
fig: Paleontological evidence
Paleontology is the study of fossils. Fossils are the dead remains of the past organisms either buried under earth crust or hardened into rocks. Fossils are formed in the stratified or sedimentary rock. so, fossil derived from deepest strata would be the oldest one. Fossil may be found in various form like an unaltered fossil, petrified fossils, impression fossil, gastrolith, coprolite. Fossil record provides following evidence to the evolution;
- Fossils are the clear picture of ancient life.
- Fossils record support the gradual and progressive evolution.
- Fossil of some intermediate form indicates the evolution of one group of organisms from another.
- The fossil record also indicates the existence of organisms in past which are now extinct.
- Fossils record shows the existence of the different group of organisms in different time period. From this, it is cleared that all organisms were not evolved at once.
- The fossil provides clear evidence about the structure of extinct organisms.
- Fossil also provides clear evidence of the habit and behaviour of extinct organisms.
Organisms which have undergone very little change over the long geological time period are called living fossil. Eg; Limulus, Peripatus, Nautilus, Sphenodon, Gingko (plant).
fig: Embryological evidences
- Development of all multicellular organisms from zygote indicates a common origin and progressive evolution of organisms.
- The embryo of all vertebrates looks similar in their early stage. It indicates the close relationship between vertebrates.
- Embryo often contains the structure which is absent in adult. Eg; Embryo of bird contains tooth buds. It indicates their evolution from toothed ancestor. Similarly, the embryo of whale contains hair that indicates their evolution from the hairy ancestor.
- A presence of a notochord, pharyngeal gill slits and postanal tail, an embryo of all chordates indicates their close relationship.
- Recapitulation theory/ Biogenetic law: It was first given by Von Baer in 1828 which was later called biogenetic law by Ernst Hackel in 1866. It states that"ontogeny repeats phylogeny".Ontogeny is life history whereas phylogeny is the evolutionary history of organisms.It means all organism repeats its evolutionary history during the development. Eg; In the lifecycle of the frog, fish-like tadpole stage occurs which is aquatic, respire through gills and can also swim. It indicates their evolution from fish-like ancestors.
Biochemicals are the components of protoplasm. The similarity in biomolecules among the different group of organisms is called molecular homology. It indicates the common origin and gradual evolution of organisms. Some biochemical evidence is:
- The basic component of protoplasm in all organisms are similar as it contains carbohydrate, protein, fat, nucleic acid etc. It indicates that during the evolution basic component of life remains unchanged.
- Enzyme-like trypsin is present from protozoa to mammals. Amylase is present from Porifera to mammals. They are chemically similar.It also indicates the close relationship of organisms.
- Hormones like thyroxine are common among all vertebrates. Similarly, insulin is common among all mammals.
- Muscle of invertebrate contains arginine phosphate whereas muscle of vertebrate contains creatine phosphate. But Balanoglosus contains both which indicates the connecting link between invertebrate and vertebrate.
Serology is the study of serum. The serum is a thin fluid of blood except blood vessels. It contains varieties of proteins. Closely related organisms contain the similar type of protein in their serum. The antibody produced against an antigen of serum is called antiserum. If human antiserum is mixed with blood, white precipitation occurs, If it is mixed with the blood of ape again white precipitation occurs. It indicates the close relationship between ape and human. Whale was supposed to be a fish, but serological test indicates its close relationship between mammals.