Chin
The chin is the forward pointed part of the anterior mandible (mental region) below the lower lip. A fully developed human skull has a chin of between 0.7 cm and 1.1 cm.
Evolution
The presence of a well-developed chin is considered to be one of the morphological characteristics of
Functional perspectives
Robinson (1913)
Developmental perspectives
Recent works on the morphological changes of the mandible during development[8][9][10] have shown that the human chin, or at least the inverted-T shaped mental region, develops during the prenatal period, but the chin does not become prominent until the early postnatal period. This later modification happens by bone remodeling processes (bone resorption and bone deposition).[11] Coquerelle et al.[9][10] show that the anteriorly positioned cervical column of the spine and forward displacement of the hyoid bone limit the anterior–posterior breadth in the oral cavity for the tongue, laryngeal, and suprahyoid musculatures. Accordingly, this leads the upper parts of the mandible (alveolar process) to retract posteriorly, following the posterior movement of the upper tooth row, while the lower part of the symphysis remained protruded to create more space, thereby creating the inverted-T shaped mental relief during early ages and the prominent chin later. The alveolar region (upper or superior part of the symphysis) is sculpted by bone resorption, but the chin (lower or inferior part) is depository in its nature.[11] These coordinated bone growth and modeling processes mold the vertical symphysis present at birth into the prominent shape of the chin.
Recent research on the development of the chin[12] suggests that the evolution of this unique characteristic was formed not by mechanical forces such as chewing but by evolutionary adaptations involving reduction in size and change in shape of the face. Holton et al. claim that this adaptation occurred as the face became smaller compared to that of other ancient humans.
Other perspectives
Robert Franciscus takes a more anthropological viewpoint: he believes that the chin was formed as a consequence of the change in lifestyle humans underwent approximately 80,000 years ago. As humans' hunter-gatherer societies grew into larger social networks, territorial disputes decreased because the new social structure promoted building alliances in order to exchange goods and belief systems. Franciscus believes that this change in the human environment reduced hormone levels, especially in men, resulting in the natural evolution of the chin.[13]
Overall, human beings are unique in the sense that they are the only species among primates who have chins. In the paper The Enduring Puzzle of the Human Chin, evolutionary anthropologists James Pampush and David Daegling discuss various theories that have been raised to solve the puzzle of the chin. They conclude that "each of the proposals we have discussed falter either empirically or theoretically; some fail, to a degree, on both accounts… This should serve as motivation, not discouragement, for researchers to continue investigating this modern human peculiarity… perhaps understanding the chin will reveal some unexpected insight into what it means to be human."[14]
Cleft chin
The terms cleft chin,
A cleft chin is an
There is a possible genetic cause for cleft chins, a genetic marker called rs11684042, which is located in chromosome 2.[22]
In Persian literature, the chin dimple is considered a factor of beauty and is metaphorically referred to as "the chin pit" or "the chin well": a well in which the poor lover is fallen and trapped.[23]
Double chin
A double chin is a loss of definition of the jawbone or soft tissue under the chin. There are two possible causes for a double chin, which have to be differentiated.
In overweight people, commonly the layer of
Another cause can be a bony deficiency, commonly seen in people of normal weight. When the jaw bones (
See also
- Chin augmentation (genioplasty)
- Masseter
- Mastication
- Otofacial syndrome
- Ptosis (chin)
References
- ^ Stringer CB, Hublin JJ, Vandermeersch B (1984). The origin of anatomically modern humans in western Europe. In F. H. Smith & Spencer (Eds.), The origins of modern humans: a world survey of the fossil evidence. New York. pp. 51–135.
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: CS1 maint: location missing publisher (link) - S2CID 2656256.
- ^ Robinson L (1913). "The story of the chin". Knowledge. 36: 410–420.
- S2CID 85195021.
- ^ DuBrul EL, Sicher H (1954). The Adaptive Chin. Springfield, IL: C.C. Thomas.
- PMID 21404235.
- S2CID 28529235.
- PMID 20807267.
- ^ PMID 24260566.
- ^ S2CID 38431987.
- ^ a b Enlow DH (1990). Facial growth. 3rd edition. Philadelphia: Saunders.
- PMID 25865897.
- ^ "Why we have chins: Our chin comes from evolution, not mechanical forces". ScienceDaily. April 13, 2015. Retrieved July 28, 2018.
- S2CID 35862039.
- ^ a b c d Mammalian Phenotype Browser: Cleft chin
- ^ Sharks of the world, Vol. 2, p. 143; by Leonard J. V. Compagno, Food and Agriculture Organization of the United Nations, 2001.
- ^ Rob Roy, p. 229 (in 1872 edition, pub. Osgood); by Sir Walter Scott, 1817.
- ^ "Myths of Human Genetics: Cleft Chin".
- ^ Online Mendelian Inheritance in Man (OMIM): 119000
- ^ Starr B (September 3, 2004). "Ask a Geneticist - Other Traits". Understanding Genetics. TheTech. Retrieved 2007-07-01.
- .
- ^ "Cleft Chin | AncestryDNA® Traits Learning Hub". www.ancestry.com. Retrieved 2022-02-26.
- ^ چاه زنخدان the chin well Archived 2014-08-08 at the Wayback Machine
- ISBN 1-58890-334-6.)
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: CS1 maint: multiple names: authors list (link
External links
- Media related to Chins at Wikimedia Commons