MODERN EVOLUTIONARY THEORY
A Modern evolutionary theory is based on the combination of natural selection and gentle origins of variation.
The modern evolutionary theory can be summarized in the following statements
- There exist variation in a species population
- Some of the variations have a special survival advantage.
- Individuals with favourable variation are more adapted to the environment than others.
- The individuals have to struggle for existence in the environment
- The main cause of variation is mutation and recombination.
FORMATION OF NEW SPECIES
The process by which new species are formed is called speciation. speciation is a continuous process because new species always evolve from old ones. speciation occurs in various ways which are mutation and isolation.
FORMATION OF A NEW SPECIES BY MUTATION
Mutation is a sudden change in the structure of DNA. This cause a change in the protein formed and hence a change in the phenotype of the species concerned.
The sudden appearance of a distinct trait or character in a large population of an organism can cause variation in that population. Mutation can only be inherited when it occurs in the gene or gametes leading to production and perpetuation of new species. Mutation elsewhere in the body cannot be passed on or inherited.
FORMATION OF A NEW SPECIES BY ISOLATION
If a member of a species is separated into two or more population by natural barriers like desert, mountain, oceans and rivers for a long, their gene may change to the extent that they cannot interbreed again to produce viable offspring and the population thereby may have produced new species.