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Has the mechanical explanation of headlock defense ever been discussed by scientists to explain the chin(protuberantia mentalis)? A mechanical advantage that prevents death and being beaten up by another male would undergo a type of topological optimization that could be measured.

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Positions where an assailant wraps his arm around a defendant's neck constitute 3/4rs of professional wrestling submissions. It's even more prevailant in amator wrestling where the contestants don't learn conplex arm and leg locks, in children, and in young adults.

When the neck is lowered, arm is barred from the neck, and the commentator shouts"will he manage to keep his chin down"

That kind of defense of the neck with the chin lowered can last 2-3 minutes, after which time the assailant's arms tire and the position changes.

The chin can therefore play a major role in human defense, mate selection, dominance tussles, and it's morphology may be designed to be vertically long and lower into the solar plexus.

There is a pit at the top of the sternum into which the chin fits when it is lowered.

Any kind of space under the chin can serve as leverage to push the head upwards and access the neck, so a chin that specificially points downwards flush with the solar chest and which deflects the arm upwards towards the mouth is an advantage to humans.

The chin size is promoted by testosterone which happens to be a hormote that encourages fighting.

The human chin is more powerful than in all other primates and can withstant more PSI force, which suggests that it is made to withstand a lot of clunking damage.

Actually 70 percent of paleolithic mandibular fractures could derive from fighting, that's in line with today's epedimeology figures, minus car accidents.

I believe that the chin comes from a range of selective factors, and i am curious about it's topological optimization, they precise shape and it's mechanical advantage. I believe that the current theories are true, and I wouldn't be surprised if the defense of westling positions can account for a lot of it's precise shape similar to a snow plough and it's alignment with the chest.

If any anthropologists are vaguely entertained by this theory the effectiveness of the chin in wrestling defense can be measured by studying archive of the number of successful defenses against wrestling strangleholds, which outnumber the attempts by 2-5.

Mechanism of injury of mandible fracture patients. MVC Motor vehicle collision, GSW Gunshot wound enter image description here

To counter Johns odd claim about eye gouging as an alternative human wrestling action, punch damage accounts for 99% more hospital submissions than eye gouging.

Strangulation is unique to our species, so it is fitting to question: which hominids first used them? Was the bite force of a Neanderthal the previous best defense for choke holds? Is the Neanderthal physiology or mind not conducive to that kind of wrestling interaction? When did hominids develop aggression traits and cognitive forethought and a wiry physique that made choke holds possible?

Did the advent of a snowplow chin as a strangulation defense even facilitate the reduction of the jaw size of humans to it's present scale?

Anthropologically, human faces are not level with the genitals, as in dogs and monkeys, who inspect each other's genitals to gather information about their sexual state. Humans communicate with the eyes diverted towards the mouth, and face, they express their sexual state with mouth movements, side motions, and an array of gestures. The Chin also serves a display purpose in that end, so mechanical forces are not the only things that should be considered, but they count alot!! The development of complex facial expressions to describe sexual communication may have also encouraged the formation of a robust chin.

A lower and more forwards pointed chin protects the neck better, other animals develop pronounced features related to their rutting combats, crabs with a large arm, antlers, https://www.sciencedaily.com/releases/2012/07/120726142202.htm

Children learn head locks from an early age, head locks are a combat action singular to humans.

The human jaw is as strong or stronger than that of other primates. The incisors can deliver 70 PSI to the chin, and a human punch can deliver 1700 PSI. 6Mpa is about 800 pounds.

The chin serves as a crash guard to intercept whacks at the apex of the triangle, It is used as a life saving neck guard in the most common wrestling submission by providing no leverage under the jaw, and it is a masculin trait controlled by testosterone, quite contrary to the general neotenic traits of homo sapiens.

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    $\begingroup$ Chins developed long before humans (pretty much anything that has a lower jaw has a chin, even if it's hidden under soft flesh), so I doubt your hypothesis is correct. $\endgroup$ – MattDMo Dec 22 '16 at 18:00
  • $\begingroup$ Are you sure that your vote to close the question is not related to our heated disagreement on the other thread? you were inaccurate about the age of menarche, because you overlooked that urban medieval late development was due to malnutrition compared to paleolithic times. Again you are wrong about chins. The science correspondant from the BBC states: It becomes even stranger when you consider that among the all primates – including our extinct relatives – only we have chins. ... So honestly i believe that your comment is not related to actual knowledge and accuracy, which is quizzical. $\endgroup$ – com.prehensible Dec 22 '16 at 18:13
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    $\begingroup$ it's hard for me to see how this could be tested ... what stops it from being an evolutionary Just-So story? $\endgroup$ – Ben Bolker Dec 22 '16 at 20:16
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    $\begingroup$ @comprehensible I had forgotten all about that question. Votes are on the question, not the questioner. I still think this question is opinion-based, as the question "Why did this feature evolve like so?" Is almost impossible to answer. $\endgroup$ – MattDMo Dec 23 '16 at 15:42
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    $\begingroup$ Stackexchange is not a forum for extended discussions - it is in a question-answer format. This question seems to either look for the confirmation of a posed hypothesis or is discussion, which to me would both seem off topic. $\endgroup$ – Gerhard Dec 24 '16 at 16:14
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No We know why the chin exists, the jaw has to be strong to be stable and not twist during under strain. humans have tiny jaws, large tongues, and sharply angled neck that leaves no room for a large enough interior ridge, so the jaw has to protrude forward or get taller to compensate. Our large facial muscles and tongue encourage the former, as does the overall shrinking of the face and jaw. The development of the chin lines up perfectly with the shrinking of the jaw and face and expansion of the tongue in hominid evolution.

Now the size of the chin may very well be influenced by sexual selection, your hypothesis might even fall into this if you had any evidence. sexual selection could exaggerate it once present, but we know why the chin originates.Like everything in evolution there are multiple factors at play but you have yet to show yur ideas is even a factor much less an important one.

For your idea to hold water you need to show several things.

  1. That headlocks are a significant and persistent problem in human history. Which is unlikely given how many skeletons are known that were killed with weapons.

  2. That the chin actually does protect against it, especially more than say a wider neck or taller jaw, which we lost.

  3. If it does help and headlocks were a significant problem, why does the size of the chin varies so much.

  4. Why the chin develops so much later than the when the neck shrank, which is when humans would have started being vulnerable to headlocks.

  5. That other explanations are not better supported.

Also there are lots of ways to kill someone while "wrestling", statistics from a sport competition with restrictive rules are not helping your case. I can't claw someone's eye out or stab them in the UFC. And I want you to think of why a human seeking to kill another would forgo the many weapons they would have, to wrestle them instead. especially why this would would happen so often a defense would need to evolve.

All you ever wanted to know about the chin

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  • $\begingroup$ From a survey of 40 people whose measurements were plotted from toddler to adults, researchers concluded that the mechanical forces needed to chew are incapable of producing the resistance needed for new bone to be created in the jaw area. "In short, we do not find any evidence that chins are tied to mechanical function, and in some cases we find that chins are worse at resisting mechanical forces as we grow," Dr. Nathan Holton $\endgroup$ – com.prehensible Dec 23 '16 at 0:01
  • $\begingroup$ @comprehensible, Dr Holton shows the chin is not an acquired characteristic which is very different from an evolutionary adaptation. $\endgroup$ – John Dec 23 '16 at 3:20
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    $\begingroup$ I would want to see a source for headlocks end a large majority of fights, especially in pre-industrial societies. ditto for the chin playing a part in defense in such cultures. Statistics from sport fights with rules are pointless, I can't claw your eyes out or stab you in the UFC. And by your statement about men and women I'm guessing you did not read my statement about sexual selection. $\endgroup$ – John Dec 23 '16 at 3:31
  • $\begingroup$ Also not all primate males fight, but if you were right why would women have chins? sexual selection could explain the difference in sexes, we both use it after all)but if it was the only cause as you claim women should not develop chins. I also feel I should mention some neanderthal do have chins, $\endgroup$ – John Dec 23 '16 at 3:58
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    $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – WYSIWYG Dec 24 '16 at 9:36
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It's naive and wrong to state that the theories for the chin are agreed upon and and comprehended, else that protection from strangling is an impossibility in selective pressures which contribute to it's current shape:

Protective reinforcement of the hominin face is a 2014 study.

A search of google indicates that:

  • "punched police report" returns 1mn results on google
  • "choked police report" returns 7mn results on google
  • "punching police report" returns 4mn results on google
  • "choking police report" returns 14mn results on google

The previous answer is based on the impossibility that choking can be of any significance in human interaction. For the idea to have any merit, you would have to demonstrate that:

  • Chokes contribute a few percent of human tribal fatalities or tribal mate choice.

  • The downwards inflection of the bone is an arbitrary construction for reinforcement and display, and that it's non-arbitrary for protection of the larynx.

40-90% of street fights caught on camera ended up with wrestling on the floor. https://martialarts.stackexchange.com/questions/1342/is-it-true-that-most-fights-end-on-the-ground-what-is-the-evidence

Neck constrictions end 70-80% of human wrestling fights, and are common in the schools.

John suggests that eye gouging can be a major statistical result in wrestling, however eye pokes only account for 1.7 to 2.1% of all eye traumas, which is of low significance including sport which contributes most of that 1.7%, compared to jaw fractures, 42% of which are caused by assault. 13% of eye traumas are from violence, mostly from punching, but also from sticks bottles knives and weapons, and very few from fingers.

Men don't gouge their wives' eyes out in order to assert dominance in studies of domestic abuse.

"... later than the when the neck shrank ...".

The musculature of the neck changed when humans became more gracile and lithe. Their necks allow them to play the piano and contributes to their intelligence and the development of their brains.

Evolution of speech caused the hyoid bone to drop (which allows primates to breathe and drink at the same time, and prevents choking) and without the change of the larynx and the hyoid bone, we'd still garble and hoot much like our chimpanzee cousins, scientists say.

"...why does the size of the chin varies..."

The growth and forwards slant of the chin ("mental eminence" from Menton, french) vary relative to testosterone, which is a fighting, sexual appetite, and strengthening hormone, though shape of the chin doesn't vary a lot. A large majority / all sapiens have a chin which does not allow leverage under the neck compared to ancestors. Neanderthals had much more of a chin than homo heidelbergensis.

Here is an example of a skull of a man who was exposed to high levels of testosterone (right), compare to a females skull (left): enter image description here Ethnic differences of skull enter image description here

When the body was less gracile and more muscled, the arms were more articulated, Is when the chin was weaker in PSI resistance, and the superciliary arch and the skull was stronger.

Previous studies have shown that the chin could be due to a range of factors, and it might be wrong to say that defense is the only cause for selection.

It would be wrong to say that the selection pressure on the chin from fighting is known, and to say that we have measured the mechanics entirely, sexual selection is very closely associated with the chin, as women are interested in beard and chin size of males.

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Some of the information contained in this post requires additional references. Please edit to add citations to reliable sources that support the assertions made here. Unsourced material may be disputed or deleted.

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    $\begingroup$ This could really use some sources to back up its claims, and meaningful claims made from the sources it does provide. Unfortunately, most of what you've put seems irrelevant, or requires heavy speculation and misunderstanding of context to approximate a valid affirmative answer. $\endgroup$ – Harris Dec 30 '16 at 20:50
  • $\begingroup$ You only have one citation, and that is behind a paywall. Please add support for each of the claims made here. "Scientists say" is not a citation. $\endgroup$ – MattDMo Dec 31 '16 at 0:58
  • $\begingroup$ Starting with your statement "humans aren't the only animals to have a chin, so i doubt your hypothesis is correct" your contribution to this page has shown a lack of intellectual accuracy which suggests that your access as a moderator on stack exchange is a matter of couchpotato attrition and not of intellectual depth. In biology, specific terms have specific meanings, so bipedal, chin, have established meanings. Elephants are accepted as having a chin. if you blur terminology, semantics degenerate into a dulled confused perception, i just had to embelish/improve that theory while at 41'C. $\endgroup$ – com.prehensible Jan 5 '17 at 13:17
  • $\begingroup$ @comprehensible Your point about including unrelated chin examples has merit, but resist the temptation to lead that into speculative ad hominem attacks. It's a complete waste of time. Focus instead on finding strong evidence for your answer and/or deriving a strong answer from your evidence. $\endgroup$ – Harris Jan 5 '17 at 16:20
  • $\begingroup$ @Harris Weinstein, Sorry the phrases and stats are quoted from an array or results and surveys, i ll add the references, fair comment thanks. $\endgroup$ – com.prehensible Jan 6 '17 at 16:55

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