CBSE Class 10 Answered

The theory of Evolution of life :

• Various theories about the evolution of life have been proposed.
• Darwin’s theory of Natural Selection stated that nature only selects those organisms that are best-suited to the particular environmental condition; whereas Lamarck's theory states that it is the environment that brings changes in organisms.
• Darwin talked about variation but did not mention about the sources of variation. With progress in genetics the sources of variation were discovered and Darwin’s original theory of Natural Selection modified. This new theory was termed Neo-Darwinism or modern synthetic theory.

According to this theory :

1. The unit of evolution is ‘population’ which has its own gene pool.

2. The heritable genetic changes appearing in the individuals of a population are

the basis of evolution.

4. Natural selection selects the variations which helps in adapting to the environment.

5. A change in the genetic constitution of a population selected by natural selection

is responsible for evolution of a new species.

6. More offspring with favourable genetic changes are born.  This is called

‘differential reproduction’. Reproductive isolation helps in keeping species

distinct.