A textbook-level rumor of the century

 Almost everyone with a tongue has seen that magical taste map. Simply put, it is the different parts of the tongue that are responsible for tasting a variety of different flavors. The base of the tongue tastes bitter, the back half of both sides tastes sour, the front half of both sides tastes salty, and the tip of the tongue tastes sweet.
  In some cases, some knowledge is still taught by the teacher, which is completely “textbook level” common sense.
  Don’t we all want to know “why”? In fact, it’s another century of rumors, because taste maps don’t exist. There should be a lot of friends who were dazed by watching this broken map when they were young. For example, in order to avoid the bitter taste when taking medicine, the medicine is deliberately placed on the tip of the tongue that tastes sweet. As a result, I was so bitter that I began to doubt life.
  This mystery began in 1901. That year, German scientist Han D. P. Hannig conducted an experiment and published a research report. He dripped sour, sweet, bitter, and salty flavors on various parts of the tongue to detect the corresponding taste thresholds. For example, to perceive salty taste, a concentration of 0.01 mol/ml is required in one area to reach the trigger threshold, while another area requires 0.012 mol/ml. Finally, he believes that certain areas of the human tongue are more sensitive to certain tastes.
  Hannig’s chart is just the relative sensitivity of each flavor from one point to another, not a comparison with other flavors. More notably, the authors also believe that this sensitivity difference is small, and do not propose any concept of taste zoning. Moreover, the science of taste was just in its infancy, and this was not a clear scientific conclusion. At the time, the study didn’t even include umami in the discussion. Because of the umami taste, it was the fifth taste that was discovered by Japanese scientist Ikeda Kikuyo in the early 20th century. That’s exactly what sodium glutamate, or MSG, tastes like.
  After more than forty years, in 1942, Harvard psychologist Edwin Pauline translated Hannig’s report into English and redrawn the chart. And that’s when the fallacy happens. When interpreting the original data, he regarded the relative sensitivity of the icon as the absolute sensitivity. So, there is such a taste map. The sensitivity of various taste sensations corresponding to various parts of the tongue has been exaggerated many times. At that time, he also wrote these contents into his book “Sensation and Perception in the History of Experimental Psychology”. Since then, so-called “taste maps” have spread.
  It has to be said that this kind of image that looks obvious at a glance is conducive to communication. Teachers embraced the picture and took it to class to teach students about the human sense of taste. In American elementary classrooms, there are even small classroom experiments designed to emphasize taste maps. It’s even a “required course” for them. Of course, there are many people who are confused by this picture. It is obvious that there is not much difference in the tastes that can be tasted everywhere on the tongue. However, sometimes when these questions are raised, the teacher can’t answer you why, and can only pass the test with a hahaha.
  It wasn’t until 1973 that Virginia Collins of the University of Pittsburgh repeated Hannig’s experiment. Only since then have people started to refute the taste map. She examined past research and convened a new group of volunteers to test their taste thresholds for various taste molecules in different tongue regions. Different areas of the tongue in the mouths of the 15 volunteers were dripped with different concentrations of sodium chloride (salty taste), sucrose (sweet taste), citric acid (sour taste), urea and quinine (all bitter tastes). By the end of the experiment, she did find that each tongue area had different taste thresholds for various flavors. However, the difference in the threshold value of each district is very small and has almost no practical significance.
  In everyday life, this is not even as great as the individual-to-individual difference in taste sensitivity. For example, most typically, each of us has a different level of sensitivity to bitterness. The same bitter substance phenylthiourea (PTC), about 28% of people cannot taste bitterness, and 65% of people can taste it. Later, scientists also discovered that this is determined by a gene called TAS2R38, which is located on human chromosome 7.
  By the time someone came out to refute the rumor, the rumor had a history of more than 30 years. Over the past thirty years, this picture has become popular all over the world and has become common sense. The development of science is limited, and the specific mechanism of taste formation has been a mystery until the 1950s. Therefore, this fallacy not only failed to be corrected in time, but instead spread in the form of cold knowledge, which was talked about by the public.
  In fact, simply do a little experiment with your tongue to see how unreliable this map is. Because no matter the tip of your tongue or the base of your tongue, you can taste all kinds of flavors. Yet there is a collective blindness to the taste map. While the science has been questioned, this taste map is still all the rage in the culinary industry today.
  Back then, merchants introduced this picture as a scientific guide to food, especially when tasting coffee and red wine. Roll up the sides of your tongue, for example, so you can filter out the acidity in the wine. For more professional wine tasting, special wine glasses are also used. Austrian glassware designer Klaus Riedel used the taste map to create a series of red wine glasses. This wine glass has a unique curve, the purpose is to make every sip of red wine you drink land on the tongue in the most correct place. And these red wine glasses put on the coat of science have also brought a huge impact on the wine industry.
  Even though the science of taste maps has been greatly reduced today, this elegant and chic wine glass is still in vogue. Sometimes this red wine glass can feed back the taste map and help the map spread further. So what should a real taste map look like?
  There are four kinds of papillae on the back and sides of mammalian tongue, they are contour papilla, leaf papilla, fungus papilla and filiform papilla. In addition to the filiform papilla, the other three types of lingual papilla are also called “taste papilla” because they contain taste buds. These onion-like taste buds are the key structure in our ability to taste.
  Taste is produced through taste receptor cells. These cells can recognize different taste molecules, encode them into electrical nerve signals, and finally transmit them to the brain through special sensory nerves to form taste sensations, so that we can perceive and distinguish various tastes.
  The taste receptor cells are concentrated in taste buds, and each taste bud contains 50 to 150 receptor cells. The number of taste buds on the human tongue is very large, ranging from 8,000 to 10,000. It is certain that the tongue and tongue edges are particularly sensitive to taste because these areas contain more taste buds. The distribution of taste buds is also very wide, almost all over the tongue, and even the upper jaw and throat have its traces.
  During chewing and swallowing, food spreads along with saliva to the papilla of the tongue. Once the taste buds on the papilla of the tongue come into contact with these food molecules, the taste receptor cells on the taste buds begin to work together. There are currently three known taste cells, which can sense the five basic tastes we often say: sour, sweet, bitter, salty, and umami. In addition to the five tastes of sour, sweet, bitter, salty and fresh, there may be a sixth taste, such as fat taste, metallic taste, etc.
  If there is a taste map, it may be found across species. For all living things, survival always comes first. Taste is formed during the long evolutionary process of mammals, and each taste has its own unique meaning. Sweet means the food is rich in sugar, umami means the food is rich in protein, and moderate intake of salty taste can maintain the body’s electrolyte balance. As for the sour and bitter taste, it reminds humans that this substance may be poisonous and harmful.
  But because various mammals are in different ecological niches, they can experience different tastes. To some extent, what animals can taste is related to what food they can eat. A typical example is our favorite national treasure, the giant panda. More than eight million years ago, the ancestor of the giant panda, Lufengshi Panda, was actually a beast that loved meat very much. However, with the advent of the ice age, they were driven to certain active areas by the severe cold. The living area is shrinking and the competition is strong, which has led to pandas giving up eating meat and entering the vegetarian world.
  Fossil evidence shows that giant pandas only started eating bamboo about 7 million years ago. However, about 4.2 million years ago, their TAS1R1 gene (the fresh leaf receptor gene) was mutated and they lost their taste for glutamate. This also means that for almost 3 million years, giant pandas were forced to eat bamboo. Enduring their lust for meat, they began to nibble on bamboo like a cultivator. Another example, cats are pure carnivores, they have lost their sense of sweet taste. Therefore, they cannot enjoy the sweetness of fruits like humans. The sweet taste of sea lions, fur seals, Western Pacific spotted seals, otters, spotted hyenas, etc., which are also carnivores, has also been completely degraded. In addition, whales living in the ocean are also the most insensitive mammals. They are adapted to swallowing for a long time, and they eat in a way that does not even use their tongues. In the long run, their taste has basically disappeared except for the salty taste.
  Therefore, the taste difference of mammals is a real taste map.