What is the Meaning of Evolution in Biology
Evolution or organic evolution (Spencer, 1852) is the unfolding of nature wherein newer types of organisms develop from the pre-existing ones through modification.
Acquired Traits :
Acquired traits are those variations which an individual develops during its life time due to effect of environmental factors, use and disuse of organs and conscious efforts.
Theory of Inheritance of Acquired Characters (Lamarckism). It is the first theory of evolution that was proposed by French biologist Jean Baptiste de Lamarck. It is based on the following
- Internal Vital Force : There is a vital force in organisms which rends to change them, generally making them larger and more complex.
- Environment : A change in environment brings about direct changes in plants. It produces new needs in animals.
- New needs (Doctrine of Desires), New need being about new desires that result in changes of older and formation of new organs.
- Use and Disuse of Organs, Repeated use of an organ makes it more complex and efficient. Non-use of an organ brings about its degeneration.
- Inheritance of Acquired Characters. The traits acquired by an individual during its life time are passed on to the next generation. After several generations the accumulation of changes results in the formation of new species.
Inherited traits :
- Inherited traits are those characteristics which are passed from parents to their offspring, generation after generation because they are controlled by genes.
- There is also reshuffling of inherited variations during gemetogenesis and fertilization.
Speciation :
It is the formation of new species from an existing one due to reproductive isolation of a section of its population.
Development of reproductive isolation is basic to formation of new species. This can occur by the following methods
Physical Barrier :
A physical barrier like valley, mountain, water body, etc. develop between two populations of a species.
Two Ends of Long Range :
Subpopulations at the two ends of a long range seldom interbreed.
Mutations :
A large mutation can make some members reproductively isolated from the rest.
Genetic Drift (Wright Effect) :
It is random change in gene frequency that occurs in a small population due to fixation of certain alleles and elimination of others.