填空题. All social animals communicate with each other, from bees and ants to whales and apes, but only humans have developed a language which is more than a set of prearranged signals. Our speech even differs in a physical way of the communication of other 1 animals. It comes from a cortical speech centre which does not respond instinctively, and organises sound and meaning on a 2 rational basis. This section of the brain is unique to humans. When and how the special talent of language developed are impossible to 3 say. But it is generally assumed that its evolution must have been a long process. Our ancestors were probably saying a million years 4 ago, but with a slower delivery, a smaller vocabulary and above all a simple grammar than we are accustomed to. 5 The origins of human language will perhaps remain forever obscurely. By contrast the origin of individual languages has been 6 the subject of very precise study over the past two centuries. There are about 5,000 languages spoken in the world today (a third of them in Africa), but scholars group them together into relatively a few families—probably less than twenty. Languages are 7 linked to each other by sharing words or sounds or grammatical 8 constructions. The theory is that the members of each linguistic group have descended one language, a common ancestor. In many 9 cases that original language is judged by the experts to have been spoken in surprisingly recent time—as little as a few thousand years 10 ago.