D For millions of years, animals have communicated in countless ways — from giving off chemical signals, to performing complex dances. Humans, on the other hand, have the ability to communicate using language. However, scientists don't agree on when human language first appeared. Even if it's unclear exactly when it began, human language has developed greatly in the past century, branching off into three different types: natural, artificial, and formal language. Natural languages, also known as man-made languages, are languages that humans have developed simply out of the need to communicate with each other. Natural languages are the languages people speak, read, write, and listen to every day, such as English, Hindi, and Russian. The vocabulary and rules of these languages have developed naturally, without the influence of an author or creator modeling or changing the languages. In short, natural languages “just happen”. Artificial languages are also man-made, but they are constructed, or made, by humans who already use a natural language to communicate. The vocabulary and grammar of artificial languages don't develop naturally but are constructed by an author or creator. There're a number of reasons for constructing an artificial language. In some cases, it may be a scientific experiment in language; in other cases, it may be the creation of an artist. An artificial language may also be constructed to make communication easier between people of different nationalities. Perhaps the best example of this is Esperanto, an artificial language created in 1887 by L. L. Zamenhof that was basically meant to simplify communication between Europeans. Finally, formal languages are languages that communicate something, but they are not spoken languages like natural and artificial languages. However, like artificial languages, they are constructed. Formal languages are meant to be very precise ( 精确的 ) in what they communicate. An example of a common formal language is computer code. Computer code has its own set of very strict rules and serves only to “speak” to a computer — people cannot use it to communicate with others.