Some status positions are more desirable than others.  They are associated with greater access to wealth, power, and social esteem.

Why have societies generated social structures that incorporate structured social inequality?  Why does inequality exist?

The Conflict Explanation of Inequality --


Marx had an easy explanation for why inequality exists.  Those who are able to gain an advantage will use that advantage to preserve, enhanced, and institutionalize their privileged position -- and to pass it on to their offspring.  The slightest inequality perpetuates itself.

Marx lived and worked in the mid-19th century.  He drew many of his examples from feudal societies that used ascriptive strategies to fill status positions.  It was obvious to Marx, and to many others, that Kings had used their power to develop legal systems that worked to preserve their privileged positions...  and that Kings had worked to have the Church expound the theory that God ordained that the King and his descendants should rule.  Etc. ...
 

Conflict explanations of inequality gain great credibility when applied to societies using ascription to fill status positions.  For example, it is difficult to imagine a non-conflict type explanation for the inequality existing in South African society during apartheid
 

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Structural-Functional Explanation of Inequality --


But what of societies which have moved to an achievement strategy of filling status positions?  Why does structured social inequality seem to be such an essential component of modern societies?

To the extent that societies do live up to their achievement ideologies, a "better" explanation for inequality needs to be found.  Here is the famous (Kingsley) Davis and (Wilbert) Moore explanation:
 

• Certain positions are functionally more important than others and require special skills.
• Only a limited number of individuals have the innate attributes that, with training, can be turned into the skills needed to fill these positions.
• The conversion of attributes into skills involves a training period, often long and hard.
• To induce the talented individuals to undergo the difficult training a reward of a greater share of wealth, power, and esteem has to be offered.

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The movement from an ascriptive system to an achievement system often times did not happen peacefully.  Example:  the French Revolution.  Almost always the shift was accompanied by a major ideological shift in the society's explanation for inequality.