• Speciation  
   • Mode of Speciation/Types of Speciation  
   • Allopatric Speciation  

   • Parapatric and Peripatric Speciation  



Variations are morphological, physiological, cytological and behaviouristic differences amongst the individuals of the same species and the offspring of the same parents. They are found in all the characters and in every conceivable direction. Therefore, no two individuals are similar.
Variations do appear even in the clones and monozygotic twins. Here, they are acquired or caused by mutations. The acquired variations are usually due to the effect of environment. They are not inherited. Mutations are sudden or discontinuous inheritable variations which are produced due to errors in DNA replication.
Types of Variations:
Variations are classified variously according to:
(i) Affected Trait:
Morphological, physi¬ological, cytological and behaviouristic.
(ii) Impact:
Useful, harmful and neutral or indif¬ferent.
(iii) Parts:
Meristic (number of parts and their geometrical relations) and substantive (appearance),
(iv) Degree:
(v) Cells Affected:
Somatic and germinal,
(vi) Phenotypic (observable) and genotypic (constitutional).
1. Continuous Variations
(a) Substantive
(b) Meristic
2. Discontinuous Variations
Importance of Variations:
1. Variations make some individuals better fitted in the struggle for existence.
2. They help the individuals to adapt themselves according to the changing environment.
3. Discontinuous variations or mutations produce new traits in the organisms.
4. Variations allow breeders to improve races of useful plants and animals for increased resistance, better yield, quicker growth and lesser input.
5. They constitute the raw material for evolution.
6. Variations give each organism a distinct individuality.
7. Because of variations, species do not remain static. Instead, they are slowly getting modified forming new species with time.
8. Pre-adaptations caused by the presence of neutral variations are extremely useful for survival against sudden changes in environment, e.g., resistance against a new pesticide or antibiotic.
9. Orthogenetic (directional or determinate) variations take part in formation of new species.