Evidences of Evolution — NEB Class 11 Biology

Evidences of Evolution

Evolution

Evolution can be defined as "a slow and progressive change resulting into complexity from simple and lower organisms which has taken place during millions of years on earth". There are two types of evolution i.e. organic evolution and inorganic evolution.

1. Inorganic evolution: The gradual change of simpler non-living things into complex non-living things is called inorganic evolution.
2. Organic evolution: The gradual change of simpler living organisms into complex living organism is called organic evolution.

Patterns of organic evolution

1. Divergent Evolution (Adaptive radiation)
2. Convergent Evolution (Adaptive convergent)
3. Progressive Evolution
4. Retrogressive Evolution
5. Parallel Evolution

Divergent Evolution: It is defined as the evolution of a variety of species from a single ancestral species each of which gets adapted in different ways to different environments. It is also known as adaptive radiation.

Convergent Evolution: It is defined as the phenomenon of acquiring similar sets or characteristics in response to the adaptation to a similar environment by the individuals of two or more totally unrelated groups. As a result the organisms have different body organizations but possess superficial similarity. Eg: development of wings in insects, flying birds, mammals.

Evidence of Organic Evolution

1. Evidences from morphology, comparative anatomy and vestigial organs
   1. Evidences from analogous organs
   2. Evidences from homologous organs
   3. Evidences from vestigial organs
   4. Evidences from atavism (Reversion)
2. Evidences from paleontology
3. Evidences from embryology
4. Evidences from geographical distribution of animals
5. Evidences from biochemistry and comparative physiology
6. Evidences from genetics

Evidence from morphology, comparative anatomy and vestigial organs

a) Evidences from Analogous organs

Analogous organs are the organs which are similar in function but different in origin. Eg: the wings of a butterfly, bird and bat.

b) Evidences from Homologous organs

Homologous organs are the organs which are similar in origin but different in functions. Eg: forelimbs of whale, bat, bird.

c) Evidences from vestigial organs

The organs which are non-functional but might have been large and functional in their ancestors are called vestigial organs. Eg: vermiform appendix, wisdom teeth in human body.

d) Evidences from atavism (Reversion)

Sometimes in some individuals, certain characters suddenly appear which were supposed in their earlier ancestors but were lost during the course of development.

Evidence from paleontology

Paleontology deals with the study of fossils. The fossils can be defined as the remain or impressions, casts or the entire organism of plants or animals of past geological ages.

Importance of paleontology

• It explains the evolutionary history of the organism.
• It suggests that the evolution has taken place from simple to complex in a gradual way of increasing order.

Archaeopteryx

It provides the connecting link between reptiles and birds suggesting that the birds might have been evolved from reptiles. It possessed following characteristics:

• It had a beak like bird but teeth and heavier jaw like reptiles.
• It had feathers like birds but also had scales like reptiles.
• It had feathery tail like birds but had tail vertebrae like reptiles.

Evidences from embryology

Embryology is the study of development of animals from egg to adult. The embryology provides evidence for the theory of organic evolution, which are given below:

1. Similarity in the early development of animals
2. Similarity in vertebrate embryos
3. Recapitulation theory (Biogenetic law)

According to Ernst Haeckel's "every organism during its development repeats the evolutionary history of its race", eg: tadpole larva of frog.