Abstract:What is the essence of content question and its evolution? This article attempts to deal with the issue by looking at the data from both spoken languages (including dialects) and sign languages. First, we focus on the discussion of a kind of content question:questions without WH words, which is composed of two types:elliptical question and topic question. Second, the multi-functions of PALM-UP in sign languages are described and analyzed, which turned out to be a preliminary form of grammatical operation. Elliptical question and PALM UP share some features like less grammaticalized, but differ in some ways:PALM UP has form and independent usage, which signifies both ‘emptiness of a constituent’ and ‘turn-giving’, two essential semantic roles demanded by content question. Therefore, we propose the hypothesis of Double Wheel Drive, i.e. the earliest form of content question is elliptical-PALM UP, which further develops into two directions:the question particles and general WH words. Most of the languages have developed a rich system of WH words, however, only a few have a complete system of WH particles, which are represented by Chinese, Russian etc.