American sitcoms have evolved to reflect the changing face of the fundamental social "situation" -- family.

Americans' changing attitudes toward sex, women's rights and gender identity have been mapped out with remarkable clarity on the sitcom screen.

By the 1990s, sitcoms about friendship became the vital force driving the genre -- and in many ways, pop culture. But earlier shows set the stage for this trend.

Sitcoms evolved in endlessly humorous ways as Americans' relationship with their jobs changed -- especially as women broke through countless workplace barriers.

Pioneering sitcom creators and stars have opened viewers' minds to the problems of racial injustice and representation -- but it has been a long, hard road.

The American Dream of social mobility is so often beyond reach that sitcoms have used humor to help audiences find laughter in the struggles of getting ahead.

Sitcom characters who are outsiders -- such as aliens, witches, nerds or teens -- have given viewers permission to laugh at their own foibles in relatable ways.

As antidotes to fear in a fast-changing world, what sitcoms offer an escape from -- and what visions they escape to -- reveal insights into the American psyche.