SPECIATION -

• Origin of new species: An isolated population of a species independently develops different types of mutations.
• The later accumulate in its gene pool. After several generations, the isolated population becomes genetically and reproductively different from others so as to constitute a new species.
• The million of different species that exist today did not emerge by any single sequence of events but have come into existence by following types different paths of speciation.

1.       PHYLECTIC SPECIATION -

• Darwin entitled his great book.
• For Darwin, speciation was the simple, gradual accumulation of changes in a lineage throughout time, until the group was distinct enough to be considered a new species. This process is now called phyletic speciation.

2.       ALLOPATRIC SPECIATION -

• It is considered as the most common type of speciation.
• Allopatric speciation typically occurs when a physical barrier i. e., a mountain range, a river, or an oil pipeline, geographically separates a population from its parental population.
• E.g., Different species of Darwin finches in the Galapagos Island.

3.       SYMPATRIC SPECIATION -

• Sympatric speciation occurs in populations where individuals continue to live among one another, even though some type of biological difference, such as the time of the year when gonads mature, has divided the members into different reproductive groups.
• The best accepted cases of sympatric speciation occur in plants as a result of polyploidy, an increase in the number of sets of chromosomes per cell occurs.

4.       PARAPATRIC SPECIATION -

• Parapatric speciation is thought to occur in populations that lie adjacent to one another.
• Gene pools diverge because the environment varies sufficiently in the different localities.
• As a result, different traits are selected in each population.