Biology Assignment Help >> Evolution

Evolution is a continuous, slow or irreversible process of change. Complex organisms are evolved from simpler organisms over millions of years. Variations in natural selection, genetic material or isolation are responsible for evolution. There are different forms of life appeared on this earth in different ages. Some of them organism had become extinct like Dinosaurs, teeth bearing birds. Whereas some others organism are still living in the same and in modified form. New organisms do not develop all of sudden from nowhere. New organism is always produced from modification of older forms. The process is slow or it requires hundreds and thousands of years to complete. Appearance of a new form of organisms from pre-existing organisms by modification is called evolution. Evolution can occur in any direction or to any degree. Commonly evolution is from simple forms to complex forms that are progressive evolution but in parasites it is from complex form to simple form.

Evidences of Organic Evolution

(A) Homologous Organs- The structures that are different in appearance or perform different functions but they have similar basic structure or developmental origin, are called homologous organs. For example:

(a)Forelimbs in vertebrates- Forelimbs of vertebrates like lizard, Frog, man, bird, whale, cat look different or perform different functions. This relationship between their structures having common basic plan or similar developmental origin is known as homology. Presences of homologous organs are as confirm:

(1) Divergent evolution

(2) Common ancestory or inter-relationship

(B) Analogous organs- The structures that are different in their basic structures or developmental origin but they appear similar or they perform similar functions are known as analogous organs. For example:

(a) Insect and bird wing-These insects or bird are different in basic structure or origin. For example bird wing is a modified forelimb, while insect wing is formed from integument but their analogous both are as flat structures and adapted for flight. Due to the Presence of analogous organs it confirms convergent evolution.

(C) Connecting links- The living organisms having the characteristic of two different taxonomic categories they are known as connecting links. For example:

(a) Tachyglossus the spiny ant eater or Ornithorhynchus the duck billed platypus both are egg laying mammals. They both act as a connecting link between reptiles or mammals.

(D)Vestigial organs-These are those types of organs of the body which are nonfunctional in the possessor, but were functional in ancestors or are functional in related animals. There are about 180 vestigial organs in man. For example mammary glands in male human beings are vermiform appendix.

(E)Atavism-It is reappearance or refunctioning of some ancestral organs that have either completed, disappeared or at present vestigial organs. For example:

(a) Development of power of moving pinna in some persons.

(b) Birth of a human baby with a small tail.

Evolution in Organisms, Biology Assignment Help

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