Social change may take plate (i) When human need change, (ii) When the existing social system or network of social institutions fail to meet the existing human needs and (iii) When new materials suggest better ways of meeting human needs.
Society is a system of social relationship which is never permanent; rather they are subject to incessant changes. The human composition of society changes over times. Thousand years ago in Asia, Europe and America the shape of society was vastly different from the shape of society thousand years later.
Biological factors bring a lot of changes for the society. Biology involves both quality and quantity of population. The change in the quality of population produces change in the society.