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Mental region (chin).png
Chin or mental region labeled in purple
ArteryInferior alveolar artery
NerveMental nerve
Anatomical terminology

The chin or the mental region is the area of the face below the lower lip and including the mandibular prominence.[1][2] It is formed by the lower front of the mandible.


Pointed chins are specific to modern humans; even very closely related species, such as Neanderthals, did not have them. The reasons for this adaptation are unclear, but a few explanations have been proposed.

Nathan Holton of the University of Iowa states, "In some ways, it seems trivial, but a reason why chins are so interesting is we’re the only ones who have them."[3] New research done by Holton shows that the evolution of this unique characteristic was formed, not by mechanical forces such as chewing, but perhaps from evolutionary adaptations involving face size and shape. Holton claims that this evolutionary adaptation occurred as our face became smaller compared to the Neanderthal-era human beings; the modern human head is approximately 15% shorter. Therefore through the change in size the chin became a factor that balanced the shape of the face.

Research on the evolution of the chin was further continued by the University of Iowa through another perspective. Opposing to Holtons scientific methods of the examination of the evolution of the chin, Robert Franciscus tackled the issue through an anthropological lens. Franciscus believed that the evolution of the chin was formed as a consequence of the change in lifestyle that was seen in human beings approximately 80,000 years ago. This was an era when human beings started to communicate more, turning their hunter-gatherer societies into agricultural societies where they increased their social networks. This decreased territorial disputes, as it further incentified the building of alliances in order to exchange goods and belief systems. Franciscus then believed that this change in the human environment reduced hormone levels, especially in men, resulting in the natural adaptation of the evolution of the chin.[3]

Overall, human beings are unique in the sense that they are the only species among hominids who have chins. In the novel, 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."[4] Through the examination of various theories that are constantly being formed, the truth about the origins of the human chin will perhaps be unraveled in the close future.

Cleft chin[edit]

Example of a cleft chin (William McKinley)
Human jaw front view

The terms cleft chin,[5] chin cleft,[5][6] dimple chin,[7][8] or chin dimple,[5] refer to a dimple on the chin. It is a Y-shaped fissure on the chin with an underlying bony peculiarity.[9] Specifically, the chin fissure follows the fissure in the lower jaw bone that resulted from the incomplete fusion of the left and right halves of the jaw bone, or muscle, during the embryonal and fetal development. For other individuals, it can develop over time, often because one half of the jaw is longer than the other, leading to facial asymmetry.[5]

A cleft chin is an inherited trait in humans, where the recessive gene, and incomplete dominance, can causes the cleft chin. However, it is also a classic example for variable penetrance[10] with environmental factors or a modifier gene possibly affecting the phenotypical expression of the actual genotype. Cleft chins can be presented in a child when neither parent presents a cleft chin. Cleft chins are common among people originating from Europe, the Middle East and South Asia.[11]

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.[12]

Double chin[edit]

Drawing circa 1900 depicting Joseph Urban as having a double chin

A double chin is a layer of subcutaneous fat around the neck that sags down and creates a wrinkle, creating the appearance of a second chin. This fat pad is sometimes surgically removed and the corresponding muscles under the jaw shortened.[13]

See also[edit]


  1. ^ "Full Definition of chin". Merriam-Webster Dictionary. Retrieved 2015-09-22.
  2. ^ O'Loughlin, Michael McKinley, Valerie Dean (2006). Human anatomy. Boston: McGraw-Hill Higher Education. pp. 400–01. ISBN 0-07-249585-5.
  3. ^ a b University of Iowa. (2015, April 13). Why we have chins: Our chin comes from evolution, not mechanical forces. ScienceDaily. Retrieved July 28, 2018 from
  4. ^ Gauger Ann. (2016, February 11) On the origin of Chins. Evolution News. Retrieved July 28, 2018 from
  5. ^ a b c d Mammalian Phenotype Browser: Cleft chin
  6. ^ Sharks of the world, Vol. 2, p. 143; by Leonard J. V. Compagno, Food and Agriculture Organization of the United Nations, 2001.
  7. ^ Rob Roy, p. 229 (in 1872 edition, pub. Osgood); by Sir Walter Scott, 1817.
  8. ^ [1]
  9. ^ Online Mendelian Inheritance in Man (OMIM) 119000
  10. ^ Starr, Barry. "Ask a Geneticist". Understanding Genetics. TheTech. Archived from the original on 2007-05-13. Retrieved 2007-07-01.
  11. ^ Günther, H. "Anomalien und Anomaliekomplexe in der Gegend des ersten Schlundbogens". Zeitschrift für menschliche Vererbungs- und Konstitutionslehre. 23: 43–52.; Lebow, M.R.; Sawin, P.B. "Inheritance of human facial features: a pedigree study involving length of face, prominent ears and chin cleft". Journal of Heredity. 32: 127–32. doi:10.1093/oxfordjournals.jhered.a105016.
  12. ^ چاه زنخدان the chin well Archived 2014-08-08 at the Wayback Machine
  13. ^ Larkin, Dimitrije E. Panfilov ; translated by Grahame (2005). Cosmetic surgery today. Stuttgart: Thieme Medical Publishers. p. 64. ISBN 1-58890-334-6.