What has been the general form of the expression of thoughts and feelings? In the form of ______

Humans have made use of various forms of communication. Generally, this expression of thoughts and feelings has been in the form of oral speech. When there is a language barrier, communication is completed through sign language in which motions stand for letters, words and ideas. Tourists, the deaf, and the mute have had to make use of this form of expression. Many of these symbols of whole words are exact and can be used internationally; speaking, however, cannot.
   Body language sends ideas or thoughts by certain actions, either intentionally or unintentionally. A nod means approval, while shaking the head indicates a negative reaction.
   Signal flags, Morse code, and smoke signals are other forms of communication. Road maps and picture signs also guide, warn, and instruct people.
   While speech is the most common form of language, other systems and techniques also express human thoughts and feelings.
What has been the general form of the expression of thoughts and feelings?