This question is primarily testing IDIOMS and WORD CHOICE.

The investigations of many psychologists and anthropologists support the generalization of there being little that is a significant difference in the underlying mental processes manifested by people from different cultures.

A) of there being little that is a significant difference
B) of there being little that is significantly different
C) of little that is significantly different
D) that there is little that is significantly different
E) that there is little of significant differences

When the underlined portion begins with (or ends with, or ends just before) a preposition, there is a good chance that the GMAT is testing word choice / idioms. This is particularly true if you see a split between a preposition and THAT.

There is an idiomatic difference between GENERALIZATION OF and GENERALIZATION THAT. The former must be followed by a noun, and is used in the following situations, as a variation on GENERALIZATION ABOUT:
The movie's generalizations of teenagers were overly simplistic.

GENERALIZATION THAT must be used whenever the generalization you're describing is an action - a CLAUSE.
I disagree with the generalization that all teenagers are selfish.

It is stylistically awkward to convert a clause into a gerund with "being," so we need "that" in this context. Eliminate A, B, and C.

Between D and E, the difference is again idiomatic. We can say "there is little difference" or "there is no significant difference," but we cannot say "little of significant differences." Eliminate E.

The correct answer is D.