David shares the question and the idea: Homo sapiens is the only species that has a chin and science has no explanation as to what the evolutionary advantage of such a "facility" is and how it works. "My hypothesis is that this bony ridge is a lever that allows the muscles surrounding the mouth to produce certain sounds that enrich the expression of the sound language in humans (perhaps specifically the "exploding" consonants bmp)?"
It is difficult to see how the chin helps in pronouncing the letter Beit Dagosha or PA. Two sounds created by the air current breaking the lips without any special involvement of the chin. In addition, the jaw muscles do not cling to it and it does not add movement capabilities. The riddle is indeed annoying, no monkey has a chin and even our Neanderthal brother managed without it. Why did such a strange decoration grow on the lower jaw? As is the way with evolutionary puzzles, many explanations have been offered to Chin.
First, beware of the logical fallacy of attributing a goal, or evolutionary adaptation to any structure. The fact that some characteristic exists (or even serves a purpose in the present) does not necessarily mean that the structure evolved as a means to a unique need.
It can be assumed, for example, that the chin is a "genetic accident", that is, a mutation that was preserved and took over a small population that would eventually multiply to create all of humanity. Such cases of genetic drift, i.e. a gene that does not have a survival advantage that nevertheless succeeds in spreading, are not rare. Examining the trajectory of the development of the jaw and the rate of change that occurred in it is not compatible with the random drift hypothesis and requires a biological factor that directed the growth of the chin. Another hypothesis is that the chin is an anatomical "spandrel". Spandrel is an architectural term: the space between the arch and the frame of the building. Let's imagine a person who sees walls built around arches but does not know the function of the arch, that viewer will be tempted to look for a purposeful, architectural purpose for these parts of the wall which are nothing more than a side result of placing a rounded arch in a square frame. The chance of such a failure will increase if our observer finds that these structural parts have been used. Is the chin a kind of spandrel of jaw design?
Change in the blink of an evolutionary eye
The human face has undergone dramatic change in the brief evolutionary blink of an eye. The brain grew and had nowhere to grow except at the expense of the jaws and chewing muscles. Some attribute the dramatic reduction of the jaws to control, which was perfected in the fire and the transition to cooked food. Some associate the refinement of the face with the transition to complex social systems where restraint of emotions and cooperation is required. In order to curb the aggression and control struggles so typical of chimpanzee groups, for example, a decrease in the levels of the male sex hormone testosterone and its receptors on the cell membranes was required. Testosterone plays a role in bone growth and a decrease in its activity also led to the reduction of the lower jaw and changes that finally pushed the chin forward.
The miniaturization process that the face went through bypassed the tongue. Our miniature mouth houses a tongue similar in size to the one that roamed the mouths of our ancestors with huge jaws until it fills the entire mouth cavity when it is closed. Not only did the tongue not pass the small one coordinated with its environment, but human speech burdened it with an additional task, tongue movement is required for pronouncing consonants such as D, Z, T, L, N, S, C, T in the Hebrew language (Makhtashi consonants). Evolution behaved like a traveler forced to fit a lot of luggage into a small suitcase: it compressed. Tracking the stages of development of the pharynx during the fetus and in the first months of life shows that the design of the chin occurs simultaneously with the lowering of the base of the tongue and the tongue bone (hyoid bone) together with the voice box downwards down the throat. This descent enriches the human voice because it has an added resonance cavity and speech: the chinless Neanderthals could produce fewer consonants than us. Such a dense organization in the back of the pharynx forces the muscles above the tongue bone ( suprahyoid muscles ) to press on the growing lower jaw and create the forward tilt that is the characteristic signature of the human chin.
But there are those who refuse to see Chinter Serah as excess, a kind of leftover construction material left behind by a hasty renovation contractor.
Maybe the function of the chin is to help with chewing?
Since the main function of the jaw is to chew, it makes sense to look for the function of the chin there. Some speculate that the chin provides mechanical support to the thin jaw and makes it possible to spread the bending and compression efforts as far as the molar teeth are in action. Computer simulations of stress distribution in a theoretical jaw without a chin compared to a real jaw did indeed show an improvement in durability. But the chin is not static: it is pushed forward during the growing years. If there is indeed a mechanical role for the forward thrust of the human chin (as opposed to, for example, the Neanderthals' chin which faces backwards), then one should expect an improvement in the jaw's resistance to bending pressures generated by the use of safes between infancy and the end of puberty around the age of 20. Monitoring the changes in jaw strength did not reveal such an improvement, contrary to the hypothesis.
Decoration?
And there are those who see the chin as an ornament: the male chin is wider and more prominent and may have been used as a sign of strength and health when choosing a partner. The problem with the chin as the peacock tail of the human face is that it is covered with a beard who hides him from the partner's eyes.
Well, to this day, David, science does not have a clear answer as to whether the chin is an organ with a purpose or a byproduct of other developmental processes. Feel free to stroke your center as you come up with a new hypothesis for this puzzle.
Did an interesting, intriguing, strange, delusional or funny question occur to you? sent to ysorek@gmail.com
More of the topic in Hayadan:
4 תגובות
The chin is designed to allow the transfer of the shaving foam in the middle of the application process from the palm to the fingers, which makes it easier to finish the process.
Response to Rumi:
The individual only came into real expression with the development of psychology according to Freud, so your theory is questionable...
This is proof of the creation of man by Adam.
Adam created man in the image of God.
In the Book of Zohar, the body of Adam is described as well as his chin and that is why only humans have a chin and not animals that were not created in the image.
The Jews have a more godly chin than Gentiles because they are more in the image of God.
Those who know what morphopsychology is can say that chin represents opinionatedness,
Early species of early man did not have a personal opinion, the individual was less expressed