When a field is selected, its entire path is selected. For example, if someone selects Nuclear physics:

both Natural sciences and Physics are automatically selected as well.

When a search is performed, translators are ordered based on the proximity of their expertise to the searchers' entered subject matter. For example, if a searcher enters Nuclear physics as the subject matter of his work, a translator with expertise Physics will show up higher in the results than a translator with expertise Natural sciences; and they will both be higher than a translator with some unrelated field (eg:Humanities) (ceteris paribus).