Social inequality began with the emergence of horticulture and pastoral societies. For the first time people had reliable sources of food and the population increased. Not all members of the societies needed to be involved in the production of food and people were free to choose their occupation. In the agriculture societies that followed, the division of labour resulted in job specialisation where people valued certain jobs more than others. The industrial revolution that started in the 18th century further differentiated people according to their wealth and occupation.
Social stratification can be organised in terms of class, gender, race and ethnicity, age or disability. Social classes based on the economic differences between groups in terms of income and wealth, possession of material goods, occupation and status. This type of stratification is and open system. People are born in a certain class but can move up or down between the different layers. This change of class is called social mobility. People I higher social classes have better access to health, better education, housing and work conditions.
There are two main theories about the formation of classes and the class conflict, the Marxist and the functionalist. The Marxist theory was created in the early to mid 19th century by the German philosophers Karl Marx (1818-1883) and Friedrich Engels (1820-1895).