who replaces who?

The following sentence comes from lesson 44, the book 4 of New Concept English:

It is only in the study of man himself that the major social sciences have [color=red]substituted the study of one local variation, that of Western civilization.

In a Chinese version of this textbook, it is interpreted in this way: the study of whole mankind, in the major sciences, has been replaced with that of a local variation.

How it could be, i wonder. it seems for me that the study of local variation has been replaced by the major social sciences. --am i right, or not?

the entire paragraph is as below:

The study of custom can be profitable only after certain preliminary propositions have been accepted, and some of these propositions have been violently opposed. In the first place, any scientific study requires that there be no preferential weighting of one or another of the items in the series it selects for its consideration. In all the less controversial fields, like the study of cacti or termites or the nature of nebulae, the necessary method of study is to group the relevant material and to take note of all possible variant forms and conditions. In this way, we have learned all that we know of the laws of astronomy, or of the habits of the social insects, let us say. [color=red]It is only in the study of man himself that the major social sciences have substituted the study of one local variation, that of Western civilization.

With the context you provided, I have the same interpretation as the Chinese version of the textbook. Here, the author complains that the study of man is based only on the Western variation.

thank you, diverhank, i got it.