Editing Antler (section)

== Structure and development ==
[[File:KaempfendeHirsche-2-cropped.jpg|thumb|right|Male [[fallow deer]] fighting]]
[[File:Sambar deers Fighting Silvassa.jpg|right|thumb|Two sambar deer fighting, [[Silvassa]], India]]Antlers are unique to [[cervid]]s. The ancestors of deer had [[tusk]]s (long upper [[canine tooth|canine teeth]]). In most species, antlers appear to replace tusks. However, one modern species (the [[water deer]]) has tusks and no antlers and the [[muntjac]]s have small antlers and tusks. The [[musk deer]], which are not true cervids, also bear tusks in place of antlers.<ref name=Hall/>

In contrast to antlers, [[horn (anatomy)|horn]]s—found on [[pronghorn]]s and [[Bovidae|bovids]], such as sheep, goats, bison and cattle—are two-part structures that usually do not shed. A horn's interior of bone is covered by an exterior sheath made of [[keratin]]<ref>{{Cite web |last=Love |first=Heather |title=What Is The Difference Between Horns And Antlers? |url=https://indianapublicmedia.org/amomentofscience/horns-versus-antlers.php |access-date=December 5, 2020 |website=A Moment of Science – Indiana Public Media}}</ref> (the same material as human [[fingernails]] and toenails).

Antlers are usually found only on males. Only reindeer (known as caribou in North America) have antlers on the females, and these are normally smaller than those of the males. Nevertheless, fertile [[wiktionary:doe#English|does]] from other species of deer have the capacity to produce antlers on occasion, usually due to increased testosterone levels.<ref>[http://www.das.psu.edu/research-extension/deer/photos/antlered-doe Antlered Doe] {{webarchive |url=https://web.archive.org/web/20120229040529/http://www.das.psu.edu/research-extension/deer/photos/antlered-doe |date=February 29, 2012 }}</ref> The "horns" of a [[pronghorn]] (which is not a cervid but a [[Antilocapridae|antilocaprid]]) meet some of the criteria of antlers, but are not considered true antlers because they contain [[keratin]].<ref>{{cite web|url=http://www.sandiegozoo.org/animalbytes/t-pronghorn%7C|title=Mammals: Pronghorn
|publisher=San Diego Zoo|access-date=June 27, 2013}}
</ref>
[[File:Red deer stag velvet.jpg|thumb|upright|An antler on a red deer stag. Velvet covers a growing antler, providing blood flow that supplies oxygen and nutrients.]]

Each antler grows from an attachment point on the skull called a pedicle. While an antler is growing, it is covered with highly [[Blood vessel|vascular]] skin called [[Velvet antler|velvet]], which supplies oxygen and nutrients to the growing bone.<ref name=Hall>{{Cite book | last = Hall | first = Brian K. | year = 2005 | title = Bones and Cartilage: Developmental and Evolutionary Skeletal Biology | publisher = Academic Press | chapter = Antlers | pages = 103–114 | isbn = 0-12-319060-6 | chapter-url = https://books.google.com/books?id=y-RWPGDONlIC&pg=PA103 | access-date = November 8, 2010 }}</ref> Antlers are considered one of the most exaggerated cases of male secondary sexual traits in the animal kingdom,<ref name="Malo">{{cite journal |doi=10.1098/rspb.2004.2933 |pmid=15695205 |pmc=1634960 |title=Antlers honestly advertise sperm production and quality |journal=Proceedings of the Royal Society B: Biological Sciences |volume=272 |issue=1559 |pages=149–57 |year=2005 |last1=Malo |first1=A. F. |last2=Roldan |first2=E. R. S. |last3=Garde |first3=J. |last4=Soler |first4=A. J. |last5=Gomendio |first5=M. }}</ref> and grow faster than any other mammal bone.<ref name=W&H>{{Cite book | last1 = Whitaker | first1 = John O. | last2 = Hamilton | first2 = William J. Jr. | year = 1998 | title = Mammals of the Eastern United States | publisher = Cornell University Press | page = 517 | isbn = 0-8014-3475-0 | url = https://books.google.com/books?id=5fVymWAez-YC&pg=PA517 | access-date = November 8, 2010 }}</ref> Growth occurs at the tip, and is initially [[cartilage]], which is later replaced by bone tissue. Once the antler has achieved its full size, the velvet is lost and the antler's bone dies. This dead bone structure is the mature antler. In most cases, the bone at the base is destroyed by [[osteoclast]]s and the antlers fall off at some point.<ref name=Hall/> As a result of their fast growth rate, antlers are considered a handicap since there is an immense nutritional demand on deer to re-grow antlers annually, and thus can be [[Signalling theory|honest signals]] of metabolic efficiency and food gathering capability.<ref name="Ditchkoff">{{cite journal |doi=10.1111/j.0014-3820.2001.tb00794.x |pmid=11327168 |title=Major-Histocompatibility-Complex-Associated Variation in Secondary Sexual Traits of White-Tailed Deer (Odocoileus Virginianus): Evidence for Good-Genes Advertisement |journal=Evolution |volume=55 |issue=3 |pages=616–25 |year=2007 |last1=Ditchkoff |first1=Stephen S. |last2=Lochmiller |first2=Robert L. |last3=Masters |first3=Ronald E. |last4=Hoofer |first4=Steven R. |last5=Bussche |first5=Ronald A. Van Den |s2cid=10418779 |doi-access=free }}</ref>
[[File:Geweihe Pierer.jpg|thumb|right|upright|Increasing size of antlers year on year in different European game species, 1891 illustration]]

In most Arctic and temperate-zone species, antler growth and shedding is annual, and is controlled by the length of daylight.<ref name="doi.org">{{Cite journal |last1=Rössner |first1=Gertrud E. |last2=Costeur |first2=Loïc |last3=Scheyer |first3=Torsten M. |date=2020-12-16 |title=Antiquity and fundamental processes of the antler cycle in Cervidae (Mammalia) |url=https://doi.org/10.1007/s00114-020-01713-x |journal=The Science of Nature |language=en |volume=108 |issue=1 |pages=3 |doi=10.1007/s00114-020-01713-x |issn=1432-1904 |pmc=7744388 |pmid=33326046}}</ref> Although the antlers are regrown each year, their size varies with the age of the animal in many species, increasing annually over several years before reaching maximum size. In tropical species, antlers may be shed at any time of year, and in some species such as the [[sambar (deer)|sambar]], antlers are shed at different times in the year depending on multiple factors. Some equatorial deer never shed their antlers.{{citation needed|date=November 2023}}

A 2019 study published in ''[[Science (journal)|Science]]'' identified eight genes active in antler formation that are normally associated with [[bone cancer]], particularly [[osteosarcoma]]. Additional tumor-suppressing and tumor-growth-inhibiting genes were determined to be responsible for regulating antler growth. This was taken to indicate that antler formation is more similar to a highly controlled form of cancer growth than to normal bone development.<ref>{{cite magazine |last= Pennisi |first= Elizabeth |date= 20 Jun 2019 |title= Cancer genes help deer antlers grow |url= https://www.science.org/content/article/cancer-genes-help-deer-antlers-grow |magazine= Science |publisher= American Association for the Advancement of Science |access-date= 4 November 2023}}</ref>

Antlers function as both weapons in male-male competition and as displays of sexual ornaments for females.<ref name="W&H" /><ref>{{Cite journal |last1=Morina |first1=Daniel L. |last2=Demarais |first2=Steve |last3=Strickland |first3=Bronson K. |last4=Larson |first4=Jamie E. |date=2018-04-01 |title=While males fight, females choose: male phenotypic quality informs female mate choice in mammals |journal=Animal Behaviour |language=en |volume=138 |pages=69–74 |doi=10.1016/j.anbehav.2018.02.004 |s2cid=3942922 |issn=0003-3472|doi-access=free }}</ref> Because mature antlers are no longer living during combat, antler fractures are incapable of being repaired following competition. A study in 2019 hypothesized that the periodic casting and regrowth of antlers might have evolved as a way to ensure the availability of complete antler sets to display each year.<ref>{{Cite journal |last1=Landete-Castillejos |first1=T. |last2=Kierdorf |first2=H. |last3=Gomez |first3=S. |last4=Luna |first4=S. |last5=García |first5=A. J. |last6=Cappelli |first6=J. |last7=Pérez-Serrano |first7=M. |last8=Pérez-Barbería |first8=J. |last9=Gallego |first9=L. |last10=Kierdorf |first10=U. |date=2019 |title=Antlers - Evolution, development, structure, composition, and biomechanics of an outstanding type of bone |url=https://pubmed.ncbi.nlm.nih.gov/31446115/ |journal=Bone |volume=128 |pages=115046 |doi=10.1016/j.bone.2019.115046 |issn=1873-2763 |pmid=31446115|hdl=10578/30778 |s2cid=201751091 |hdl-access=free }}</ref> Antler regeneration in male deer ensures that every mating season begins on a clean slate, as an increase in branching size and complexity happens each regeneration cycle in an individual.<ref name="doi.org"/>