Things Yoram knows: Who needs wisdom teeth?

With his mouth numb and the hum of the drill still echoing in his ears, C turns to him with a desperate question: Who needs wisdom teeth?

Well C: The truth is that no one "needs" wisdom teeth just like no one needs an appendix or armpit hair. Hardly a person has ever used their wisdom teeth to chew and yet they are there, patiently waiting their turn to cause suffering and fulfill the old curse: Ela zaal zaal dir vasfalan, nar ainar zaal dir saba-oif zanvaitik .

If there is a part of the body that is clearly seen as having fallen into the wrong body, it is the molars. This mismatch has practical consequences, there is no other body part that requires so much surgical intervention as the jaws. Surgery is defined as "a medical operation involving the cutting of tissue" and only because the procedure is so common we forget that filling, extraction or root canal treatment are surgeries for everything. The changes in the way of life since we separated from the apes required a rapid and fundamental change in the structure of the face and the result of this rapid transformation is the unfortunate state of the molars. It is easy to reconstruct the evolutionary trajectory of the wisdom teeth. There is no organ in the body that is better preserved than teeth, so the study of fossils relies a lot on the number of teeth, their size, their shape, the thickness of the enamel and the wear marks on it in order to learn about the way of life of extinct creatures, including our ancestors.

Our ancestors have big jaws

Until about five million years ago, everything was simple, as with most mammals, the incisors were used to collect food from the environment and the molars at the back were used for crushing hard parts, tearing leaves and stems and preparing the chunk for swallowing. When you need to understand raw food for swallowing, the molars, including the wisdom tooth, are essential. The need for cutting teeth capable of large bites and fangs for hunting or defense disappeared when hands took over the work of gathering and stone tools dissected the food before it even entered the mouth. The need for strong muscles weakened when we started cooking the food. The reduction of the jaws made it possible to increase the volume of the rapidly growing brain box. A mutation in the myosin protein about two million years ago weakened the chewing muscles and the biting force of our ancestors, which probably teaches about a softer diet, meaning grinding or even cooking the food. The pharynx and jaw muscles were dwarfed but another factor forced us to continue chewing.  

Homo sapiens and the pretzel

The diet of humans is very different from the diet of our relatives the chimpanzees and gorillas. The human ancestors separated from the chimpanzee ancestors. Most of our evolution took place on the plains and prairies, not in the forests. The main source of energy was again not the sugar of the fruits but the starch from grains, legumes and tubers. We are the main starch consumers (and to a large extent the only ones) among primates, until today the four most important crops in world agriculture: corn, wheat, rice and the potato are starchy foods. Unlike the sugar found in the fruit to encourage animals to eat it and thus spread the seeds, the plant produces starch to meet its own energy needs and not for export and is much harder to digest. In the language of nutritionists, the difference is in a low "glycemic value" which means that it takes time and effort to break down the starch into simple sugar that the cells can utilize. Fruits will be digested and the nutrients in them will be absorbed even if we don't chew them thoroughly and so will pieces of meat but pea or corn kernels that are swallowed without chewing will often end up in the toilet just as they entered. Our ancestors adapted to the new situation by increasing the production of starch: the enzyme that breaks down starch in saliva. To effectively utilize starchy food, the dense packaging in which it is kept must be broken and a wet pulp rich in starch must be made from it. This is how the shape of the molars changed: in the chimpanzee they are adapted to cracking hard fruits: the lower molar is the appropriate "leaf" in the peel to the upper molar which functions as a mortar (as roasted coffee is ground in the Bedouin tradition). In the gorilla that feeds on leaves, the molars are built for tearing and tearing and are accordingly serrated. The human molar tooth evolved from a "nutcracker" similar to that of the chimpanzee, but those who use the nuts for their original function: cracking pistachios run the risk of cracking. Our teeth are designed to turn food that arrived in the mouth in small pieces into a wet porridge where the chemical breakdown of the starch already begins. The contact area of ​​the molars should correspond to the amount of food to be processed and this is relative to the size of the body and the amount of energy it requires and therefore cannot be greatly reduced. This is how the molars find themselves crowded and crowded in her dwarfed jaw until the third molar is a wisdom tooth and has no possibility of erupting without quarreling with her friends who have already found a place for them. 

And why doesn't she disappear?

 Evolution manages to effectively eliminate unnecessary teeth. The ancient mammals had many more teeth: 4 incisors, a canine and no less than 5 jaws (premolars) between the canines and the molars. Since we separated from the reptiles we got rid of 2 incisor teeth and two jaws on each side of each jaw and in the mice the fangs and jaws disappeared completely. Why wouldn't Shen Habina follow them and completely ignore them if she is so disturbing?

There is no limit to the diversity in the size and shape of the mouth between different animals, but it turns out that there are fixed and common mechanisms that direct the development of the teeth. In all mammals, the molars develop from the outside in, meaning that the first tooth that forms in the jaw is the one closest to the fang, and only after that does the second and rearmost appear, meaning that the one closest to the swallowing house appears last. The tooth develops from progenitor cells in the jaw that multiply and secrete the enzyme that causes the crystallization of the hard enamel. The developing tooth secretes substances that suppress the development of the neighboring tooth. The opposing signal, which encourages tooth growth, comes from the connective tissue (mesenchyme) in the jaw This is the mechanism that ensures correct placement of the teeth side by side. The growth rate of each molar tooth and therefore the final size it will reach is determined by the ratio between the inhibition signal and the activation signal and this ratio remains constant between the first tooth and the second and between the second and third because it is controlled by the same genes. This mechanism ensures that for someone who has three molars, the second tooth will always occupy a third of the total length of the molars. The rule applies even when the three teeth are equal in size and up to the situation where there is no third molar at all (and then the length of the second molar will be half the length of the first). Measurements of the relative sizes of teeth in a large number of mammals confirmed this connection: the size of the third molar (it is the "wisdom tooth") is a function of the factors that determine the relative size of the 2 molars in front of it. When the relationship between the two "useful" molars is determined, the fate of the wisdom tooth is also determined. Most meat eaters are exempt from wisdom tooth punishment: the second molar is half as long as the first and there is no need for the third because the stomach knows how to break down protein even in relatively large chunks. The herbivores will usually have three equal molar teeth that are required for a long grinding of the cellulose and in the mouth of the omnivores there will be three molars arranged from the largest (front) to the smallest in the back. There are few examples of exceptions to this rule: the miniature monkeys of South America, marmosets and tamarins underwent a process of dwarfism during which the jaw became small and the wisdom tooth disappeared. For the disappearance of the wisdom tooth in this group, explanations related to an insect-based diet have been proposed A recent hypothesis links the number of teeth to the rate of fetal development. The pygmy monkey cubs are usually born as twins and are, accordingly, extremely small. The slowing of development in the womb, the researchers believe, resulted in the final shape of the jaw being established before the signal required for the development of progenitor cells that will produce the third molar after the development of the second molar is transmitted. A similar mechanism left the South American pygmy wolf (Speothos venaticus) with a single molar in the upper jaw. It is understood that in the human fetus, which is required for the growth of an especially large brain during pregnancy, such a mechanism is not possible, so perhaps our wisdom can be blamed for wisdom tooth pain.

The relationship between diet and jaw bone size

And maybe you shouldn't always blame the DNA. Our jaws are dwarfed not only because of the genetic load we carry but also because the modern lifestyle does not require much chewing so the muscles in the face atrophy and with them the jaws are small. A study that compared the facial features of a hunter-gatherer population in southern Argentina with their farming relatives found that a sedentary lifestyle and soft food do leave their mark on the reduction of the mouth. Researchers who raised rock faces on cooked carrots and soft apples were able to reduce the facial bones compared to their brothers who were fed the same foods in their severe condition. And a soft diet during the period of human growth affects the development of the jaw bones. It is possible that we suffer from wisdom teeth more than our ancestors and require more expensive braces and straightening treatments simply because we stopped chewing the hard part of the bread.

Thanks to: Dr. Renata Peterkova, Dr. Gabriele Macho for their help.

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