One of the unique features of human languages is that the connection between sounds and the ideas those sounds represent is arbitrary. Different words can be used to represent the same concept with equal utility, and it is often the case that words are very different between languages. Languages may be interrelated and historically connected, but this does not imply that all languages evolved out of a single original language. Even so, many early studies of human language were concerned primarily with tracing the roots language back to a single original source.