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. The quality of population of a society is controlled by the process of selection, such selection is of two types, Natural and Social selection.

Natural selection

By natural selection we mean, the selection of some individuals or groups for survival and elimination of others. Thus, nature selects only those who are strong and efficient. The weak, the inefficient and the useless people or groups are thrown out. Natural selection works at three levels. (1) Struggle against nature, (2) Struggle against other species and (3) Struggle within the same species. In the struggle for existence only the fittest survives.

Social selection

If refers to the process which creates circumstance that would influence reproduction and survival. Social selection is of two types. They are (1) Direct social selection and (2) Indirect social selection. In direct social selection man himself creates social conditions which affect the birth and death rates. For example modern man adopts family planning and limit the size of the family. In contrast in indirect social selection, society creates situation which influence the birth or death rates. But they have an impact on these.

Effects of increase in population

Increase in the size of population induces an increase of military power. The size of the population of a nation also affects its entire lifestyle. On countries where there is increased population, there occurs increased poverty. People suffer as population grows. Overpopulation may result in unemployment, beggary, housing problems, illiteracy, child labour etc. crime rates, fire accidents and the possibility of road accidents may increase. For this more and more rules and regulations would become necessary, overpopulation may threaten liberty.

Effect of decrease in population


Often under population poses a fearful problem of race suicide. The falling birth rate in countries like U.S.A. the U.S.S.R., Sweden and Iraq has created alarm in those countries.

Effects of changes in population ratio

In the societies where the female population exceeds the male population a system of polygyny is likely to the practiced. On the other hand, if the male population out numbers the female population, polyandry is likely to prevail. In a society where children and old people grow in number, the social and economic progress of that society is likely to be at stake, because more resources are to be diverted for their feeding and care. If there is only young people in a society, it is likely to be deprived of the old man’s experience and wisdom. Likewise, if the youngmen die and the oldmen survive, the country’s defence may be in danger.