The purpose of this paper is to raise the question of the relative roles of cognitive and functional factors in the evolution of grammar. The conclusion is that they have both played important roles, although unbalanced ones. Human language originated with the linking of conceptual structures and the vocal output system. In other words, cognitive factors were the first to shape grammar. But with the passage of time, the needs of communication came to play an ever-more important role in grammar. Human language today hence reflects the influence of both types of factors.