Ekman found that people in a New Guinea community with no exposure to Western media identified the same few facial expressions as Westerners did. Why is the isolation of the sample the load-bearing part of that finding?

D. Because agreement between cultures in contact could be learned.

Cross-cultural agreement is not by itself evidence of anything innate, two populations watching the same films could easily converge. Ekman's design closes that route: whatever the Fore and American undergraduates shared, they did not get it from each other. The conclusion is correspondingly narrow, covering a handful of expressions beneath a great deal that display rules govern.