What do fauvism and primitivism have in common?

They are both flattened figures. Fauvism and Primitivism are both a type of art. Primitivism is a Western art movement that uses visual forms from non-Western or prehistoric people. Fauvism was a short-lived style of painting that involved vivid uses of color. Fauvism did have an important effect on other artists.

The linear perspective changed the quality of art because it gave art a sense of reality. it gave the illusion that the background and surroundings were actually close and/or far and a sense of depth. linear perspective change the quality of art following its birth the renaissance period as they want the art to be more realistic and they believe one way to achieve it is to use the method of linear perspective. it uses the principle of math to realistically portray space and depth in art. 

Generally spontaneous human combustion is something that still bewilders some, human combustion happens very rarely and doesn't affect the surrounding areas, so unless you want to set your self on fire, human combustion will remain spontaneous and very rare.