Contribution of scientist :
$(a)$ Charles Darwin
$(b)$ Lamarck
Gave Darwin theory which state that useful variations from the organism are selected by nature i.e. natural selection and gets accumulated in the organism. This causes evolution e.g. industrial melanism, chemical resistance
Lamarck in his book 'Philosophie zoologique' ($1809$) proposed that the evolution of life form had occurred by the use and disuse of organs.
The scientists believe that evolution is gradual. But extinction, part of evolutionary story, are 'sudden' and 'abrupt' and also group-specific. Comment whether a natural disaster can be the cause for extinction of species.
What is evolution
Write short note on Darwinism.