Cultural relativism implies that cultures are isolated from each other. challenging that assumption, philosopher mary midgley says, "all cultures are formed out of many streams." what does midgley mean by this?

The answer is Cultures have always been shaped by their encounters with other cultures.

That was what Midgley meant when he mentioned "all cultures are formed out of many streams". Cultural relativism is the idea that a person's beliefs, values, and practices should be understood and is the ability to understand a culture on its owns terms and not to make judgments using the standards of one's own culture.

the factors that the economies of the muslim empires prosper were:

1- land trade routes-located between three continents  

2- sea trade routes

trade contributed to the spread of muslim empires, and with that islamic culture led to a growing feeling of internationalism resulted in the transfer of technology, science, and other cultural forms.