how is cultural change analogous to biological evolution?

This is often called social Darwinism in that different cultures have varying ideas and belief systems that govern their collective. When two differening societies come into conflict, one side will inevitably win and the culture is 'improved' over time.

In this loose regard, then, it is like biological evolutio in that the stronger culture survived while the weaker one was assimilated. This does not always hold true when human beings and culture are concerned however, because it is not biological in nature, but rather motivated by emotions and spiritual beliefs.