Why can only certain parts of the tongue taste sweet flavors? Is there an evolutionary benefit to this?

All parts of the tongue can taste every flavor. The tongue, and indeed the sides of the mouth, the epiglottis and other tissues are all covered with taste buds. Each taste bud contains many taste cells that can taste different flavors. According to the textbook "Neuroscience" edited by Dale Purves, this misconception dates back to the research of German scientist D. P. Hanig, published in 1901. Hanig simply noted down the subjective remarks of volunteers describing where they tasted a flavor. Unable to find a clear delineation of regions, Hanig recorded that certain areas of the tongue were slightly more sensitive to flavors than others based on statistically incomplete data. Other researchers interpreted his publication to mean that only certain parts of the tongue can taste certain flavors. Despite the ease of anybody disproving this theory by simply placing a pinch of salt at the tip of their tongue (which supposedly can only taste sweet), this misconception has lingered for a century. Perhaps the reason for the inability of this myth to die is the fact that a picture of a tongue with different parts colored and labeled makes for such an eye-catching image in science books. In 1905, Einstein published his landmark paper on special relativity. It is amazing that around the same time mankind was unraveling the mysteries of time travel, we were misunderstanding science that was literally on the tip of our tongue. More amazing is that this misunderstanding has persisted for over a century.