Discuss Lamarck’s and Darwin’s theories of evolution - KCSE Biology Essays

Larmarck’s theory states that when the environment demands the need or use of a particular structure in the body; the body develops it in response; for example giraffes used to have short necks; when all the grass was exhausted, they started stretching their necks in search of leaves on trees; therefore they developed long necks; which then were inherited by their offspring;

However, when a structure is not continually used, it reduces in size and becomes dysfunctional; this theory fails to explain how acquired characteristics become inherited;

Darwin’s theory suggests that in nature there occur struggle for existence; only those individuals with the desired adaptations survive; those poorly adapted fail to compete; and become extinct;

There also occurs variation in nature; where organisms with desired adaptations pass on their characteristics to offspring during reproduction; those poorly adapted fail to reach maturity; and do not reproduce; therefore, nature selects for individuals best suited to an environment; and against those poorly adapted (natural selection); as there occurs survival of the fittest;