根据下面资料，回答11-15题 <br /> The Special Ability of Human Beings <br /> Every day we experience one of the wonders of the world around us without even realizing it. It is not the amazing complexity of television, nor the impressive technology of transport. The universal wonder we share and experience is our ability to make noise without mouths, and so transmit ideas and thoughts to each other' s minds. This ability comes so naturally that we tend to forget what a miracle(奇迹) it is. <br /> Obviously, the ability to talk is something that marks humans off from animal. Of course, some animals have powers just as amazing. Birds can fly thousands miles by observing positions of the stars in the sky in relation to the time of day and year. In Nature' s talent show,humans are a species of animal that have developed their own special act. If we reduce it to basic terms, it' s an ability for communicating information to others, by varying sounds we make as we breathe out. <br /> Not that we don' t have other powers of communication. Our facial expressions convey our emotions, such as anger, or joy, or disappointment. The way we hold our heads can indicate to others whether we are happy or sad. This is so-called "body language". Bristling ( 直立的) fur is an unmistakable warning of attack among many animals. Similarly, the bowed head or drooping tail shows a readiness to take second place in any animal gathering. <br /> Such a means of communication is a basic mechanism that animals, including human beings, instinctively acquire and display. Is the ability to speak just another sort of instinct? If so, how did human beings acquire this amazing skill? Biologist can readily indicate that particular area of our brain <br /> where speech mechanisms function, but this doesn't tell us how that part of our bodies originated in our biological history. <br /> How do we explain that human beings have the ability to speak according to biologists?