Heredity and evolution class 10 notes

An elephant resembles other elephants, a rose plant looks like other rose plants, and children resemble their parents, even grandparents or great-grandparents. This resemblance among the individuals of a species has given rise to a general truth 'like begets like' which implies continuity of life. Origin of first life on earth still remain unclear because evidences are hidden in very distant past which can’t be revelled easily. The problem of creation comes under two headings, the origin of life itself and origin of the forms of life. The variety of life is tremendous; more than one million species have already been discovered. In this vast arena of life, there are widests varieties. There has been lots of presumption made since long that how life in its varied form originated.

Theory of Organic Evolution

• Many theories have been put forward to account for the existence of the various kind of animals and plants found in this universe today Primitive life was produced in the water bodies in reducing conditions from non-living materials by chemical evolution.
• Term evolution has coined by Herbert Spencer and has been derived from Latin word evolve-re which means unfold or unroll and literally means the ‘‘process of contineous change’’. Therefore, evolution is defined as a naturally occuring slow continuous and irreversible process of change.
• This term chemical evolution has replaced in organic evolution by Charles Darwin and signifies ‘Descent with modification’ which state that present complex plants and animals have evolved from earlier simpler form of life by gradual changes.
• Organic evolution means the progressive development of simple organisms to the complex organisms means origin of species and other groups from the old ones.
• According to the evolution theory there is no break in the chain of life and every thing has originated from some thing of the past. In simple words, it means that the present is the child of past and the father of the futrue in all things.