Editing Allen's rule

{{Short description|Relation of habitat temperature and limb length}}
[[File:Allens rule, Lepus, hare, ears, Earth.png|alt=Earth, ears, hare, Lepus|thumb|Allen's rule - Hare and its ears on the Earth<ref>{{Cite book|last=FRYDRÝŠEK|first=Karel|title=Biomechanika 1|publisher=VSB – Technical University of Ostrava, Faculty of Mechanical Engineering, Department of Applied Mechanics|year=2019|isbn=978-80-248-4263-9|location=Ostrava, Czech Republic|pages=338–339}}</ref>|250x250px]]
'''Allen's rule''' is an [[ecogeographical rule]] formulated by [[Joel Asaph Allen]] in 1877,<ref>{{cite journal |first=Joel Asaph |last=Allen |authorlink=Joel Asaph Allen |title=The influence of Physical conditions in the genesis of species |journal=Radical Review |year=1877 |volume=1 |pages=108–140 |url=http://people.wku.edu/charles.smith/biogeog/ALLE1877.htm}}</ref><ref>{{cite book |first=Barry Holstun |last=Lopez |year=1986 |title=Arctic Dreams: Imagination and Desire in a Northern Landscape |publisher=Scribner |url=https://books.google.com/books?id=Y-WxJYMD5HsC |isbn=978-0-684-18578-1}}</ref> broadly stating that animals adapted to cold climates have shorter and thicker limbs and bodily [[Appendage|appendages]] than animals adapted to warm climates. More specifically, it states that the body [[surface-area-to-volume ratio]] for [[Homeothermy|homeothermic]] animals varies with the average temperature of the habitat to which they are adapted (i.e. the ratio is low in cold climates and high in hot climates).

==Explanation==
[[File:Allen_rule_example.svg|thumb|Three rectangular prisms are each composed of eight [[unit cube]]s. A composite cube with a side of 2 has a volume of 8 units<sup>3</sup> but a surface area of only 24 units<sup>2</sup>. A rectangular prism two cubes wide, one cube long and four cubes tall has the same volume, but a surface area of 28 units<sup>2</sup>. Stacking them in a single column gives 34 units<sup>2</sup>.]]
Allen's rule predicts that [[endotherm|endothermic]] animals with the same body volume should have different [[surface area]]s that will either aid or impede their heat dissipation.

Because animals living in cold climates need to conserve as much heat as possible, Allen's rule predicts that they should have evolved comparatively low [[surface area-to-volume ratio]]s to minimize the surface area by which they dissipate heat, allowing them to retain more heat. For animals living in warm climates, Allen's rule predicts the opposite: that they should have comparatively high ratios of surface area to volume. Because animals with low surface area-to-volume ratios would overheat quickly, animals in warm climates should, according to the rule, have high surface area-to-volume ratios to maximize the surface area through which they dissipate heat.<!--Starting on page 67, Ashizawa et al. (2007) said, "Such differences are possibly related to differentiation of the so-called 'race' during human population dispersals, and are classically interpreted following Allen's rule (Allen, 1877). The latter can be very briefly summarized as follows: a homeothermic animal living in a hot climate has a smaller body volume-to-surface area ratio, and vice versa, as a result of thermal adaptation. Much more briefly it holds that animals adapted to cold have shorter limbs and protruding body parts."--><ref name="Ashizawa">Ashizawa, K. et al. (2007). Growth of height and leg length of children in Beijing and Xilinhot, China. In Anthropological Science. 116(1). Pages 67 & 68. Retrieved January 22, 2017, from [https://www.jstage.jst.go.jp/article/ase/116/1/116_070130/_pdf link].</ref>[[File:Comparison of surface area vs volume of shapes.svg|thumb|Graphs of {{nowrap|surface area, ''A''}} against {{nowrap|volume, ''V''}} of the Platonic solids and a sphere, showing that rounder shapes with the same volume have a smaller surface area.]]

==In animals==

Though there are numerous exceptions, many animal [[Population|populations]] appear to conform to the predictions of Allen's rule. The [[polar bear]] has stocky limbs and very short ears that are in accordance with the predictions of Allen's rule, so does the [[snow leopard]].<ref>{{cite web |first=C. Michael |last=Hogan |date=November 18, 2008 |url=http://www.igoterra.com/artspec_information.asp?thingid=36084 |title=Polar Bear: ''Ursus maritimus'' |website=iGoTerra}}</ref> In 2007, R.L. Nudds and S.A. Oswald studied the exposed lengths of [[seabird]]s' legs and found that the exposed leg lengths were negatively correlated with ''Tm''axdiff (body temperature minus minimum ambient temperature), supporting the predictions of Allen's rule.<ref name="Nudd"/> J.S. Alho and colleagues argued that [[tibia]] and [[femur]] lengths are highest in populations of the [[common frog]] that are indigenous to the middle latitudes, consistent with the predictions of Allen's rule for [[Ectotherm|ectothermic]] [[Organism|organisms]].<ref name="Alho"/> [[Population|Populations]] of the same species from different [[latitude]]s may also follow Allen's rule.<ref>{{cite journal |author-link1=Peter L. Hurd |last1=Hurd |first1=Peter L. |last2=van Anders |first2=Sari M. |date=2007 |title=Letter To The Editor: Latitude, Digit Ratios, and Allen's and Bergmann's Rules: A Comment on Loehlin, McFadden, Medland, and Martin (2006) |journal=Archives of Sexual Behavior |volume=36 |issue=2 |pages=139–141 |doi=10.1007/s10508-006-9149-9|pmid=17333323 |hdl=2027.42/83881 |s2cid=2690330 |url=https://deepblue.lib.umich.edu/bitstream/2027.42/83881/1/latitude_digit_ratios_a_comment_on_loehlin.pdf |hdl-access=free }}</ref>

R.L. Nudds and S.A. Oswald argued in 2007 that there is poor empirical support for Allen's rule, even if it is an "established ecological tenet".<ref name="Nudd"/> They said that the support for Allen's rule mainly draws from studies of single species, since studies of multiple species are "confounded" by the scaling effects of [[Bergmann's rule]] and alternative adaptations that counter the [[Prediction|predictions]] of Allen's rule.<ref name="Nudd">{{cite journal |last1=Nudds |first1=R.L. |last2=Oswald |first2=S.A. |title=An Interspecific Test of Allen's Rule: Evolutionary Implications for Endothermic Species |journal=Evolution |date=December 2007 |volume=61 |issue=12 |pages=2839–2848 |doi=10.1111/j.1558-5646.2007.00242.x |pmid=17941837|s2cid=28694340 |doi-access=free }}</ref>

J.S. Alho and colleagues argued in 2011 that, although Allen's rule was originally formulated for [[endotherm]]s, it can also be applied to [[ectotherm]]s, which derive body temperature from the environment. In their view, ectotherms with lower surface area-to-volume ratios would heat up and cool down more slowly, and this resistance to temperature change might be adaptive in "thermally heterogeneous environments". Alho said that there has been a renewed interest in Allen's rule due to global warming and the "[[Microevolution|microevolutionary]] changes" that are predicted by the rule.<ref name="Alho">{{cite journal |last1=Alho |first1=J. S. |last2=Herczeg |first2=G. |last3=Laugen |first3=A. |display-authors=etal |date=2011 |title=Allen's Rule Revisited: Quantitative Genetics of Extremity Length in the Common Frog Along a Latitudinal Gradient |journal=Journal of Evolutionary Biology |volume=24 |issue=1 |pages=59–70 |doi=10.1111/j.1420-9101.2010.02141.x |pmid=20964781 |s2cid=32746448 |doi-access=free }}</ref>

==In humans==
[[File:Eskimo group - NARA - 523819.jpg|thumb|[[Eskimo]] Group by photographer [[William Dinwiddie]] (1894)]]

Marked differences in limb lengths have been observed when different portions of a given human population reside at different altitudes. Environments at higher altitudes generally experience lower ambient temperatures. In [[Peru]], individuals who lived at higher elevations tended to have shorter limbs, whereas those from the same population who inhabited the more low-lying coastal areas generally had longer limbs and larger trunks.<ref>{{cite journal |first=Karen J. |last=Weinstein |title=Body Proportions in Ancient Andeans from High and Low Altitudes |journal=American Journal of Physical Anthropology |date=November 2005 |volume=128 |issue=3 |pages=569–585 |doi=10.1002/ajpa.20137 |pmid=15895419}}</ref>

Katzmarzyk and Leonard similarly noted that human populations appear to follow the predictions of Allen's rule.<ref name="Katzmarzyk and Leonard"/><sup>:494</sup> There is a negative association between [[body mass index]] and mean annual temperature for indigenous human populations,<ref name="Katzmarzyk and Leonard"/><sup>:490</sup> meaning that people who originate from colder regions have a heavier build for their height and people who originate from warmer regions have a lighter build for their height. Relative sitting height is also negatively correlated with temperature for [[Indigenous peoples|indigenous]] human [[Population|populations]],<ref name="Katzmarzyk and Leonard"/><sup>:487–88</sup> meaning that people who originate from colder regions have proportionally shorter legs for their height and people who originate from warmer regions have proportionally longer legs for their height.<ref name="Katzmarzyk and Leonard">{{cite journal |last1=Katzmarzyk |first1=Peter T. |last2=Leonard |first2=William R. |date=1998 |title=Climatic Influences on Human Body Size and Proportions: Ecological Adaptations and Secular Trends |journal=American Journal of Physical Anthropology |volume=106 |issue=4 |pages=483–503 |doi=10.1002/(SICI)1096-8644(199808)106:4<483::AID-AJPA4>3.0.CO;2-K |pmid=9712477}}</ref>
[[File:Mean annual temperature and brachial index in selected modern populations.jpg|thumb|Mean annual temperature and limb proportions in selected modern populations.]]
In 1968, A.T. Steegman investigated the assumption that Allen's rule caused the structural configuration of the face of human populations adapted to polar climate. Steegman did an experiment that involved the survival of rats in the cold. Steegman said that the rats with narrow [[Nasal passage|nasal]] passages, broader faces, shorter tails and shorter legs survived the best in the cold. Steegman said that the experimental results had similarities with the Arctic Mongoloids, particularly the [[Eskimo]] and [[Aleut]], because these have similar [[Morphology (biology)|morphological]] features in accordance with Allen's rule: a narrow nasal passage, relatively large heads, long to round heads, large jaws, relatively large bodies, and short limbs.<ref>{{cite journal |last1=Steegmann |first1=A.T. |last2=Platner |first2=W.S. |date=January 1968 |title=Experimental cold modification of cranio-facial morphology |journal=American Journal of Physical Anthropology |volume=28 |issue=1 |pages=17–30 |doi=10.1002/ajpa.1330280111 |pmid=5659959 }}</ref>

Allen's rule may have also resulted in wide noses and alveolar and/or maxillary prognathism being more common in human populations in warmer regions, and the opposite in colder regions.<ref>{{Cite web |last=Rae |first=Todd C. |last2=Koppe |first2=Thomas |last3=Stringer |first3=Chris B. |date=27 October 2010 |title=The Neanderthal face is not cold adapted |url=https://edisciplinas.usp.br/pluginfile.php/6200375/mod_resource/content/1/The%20neanderthal%20face%20is%20not%20cold%20adapted%20%28Rae%20et%20al%202011%29.pdf |access-date=5 May 2024 |website=Moodle USP: e-Disciplinas}}</ref>

==Mechanism==

A contributing factor to Allen's rule in [[vertebrates]] may be that the growth of [[cartilage]] is at least partly dependent on temperature. Temperature can directly affect the growth of [[cartilage]], providing a [[proximate]] biological explanation for this rule. Experimenters raised [[mice]] either at 7 degrees, 21 degrees or 27 degrees Celsius and then measured their tails and ears. They found that the tails and ears were significantly shorter in the mice raised in the cold in comparison to the mice raised at warmer temperatures, even though their overall body weights were the same. They also found that the mice raised in the cold had less blood flow in their [[Limb (anatomy)|extremities]]. When they tried [[Bone growth|growing bone]] samples at different temperatures, the researchers found that the samples grown in warmer temperatures had significantly more growth of cartilage than those grown in colder temperatures.<ref>{{cite web |title=Hot weather for longer legs |website=Science News |publisher=The Naked Scientists |date=December 2008 |url=http://www.thenakedscientists.com/HTML/content/news/news/1549/}}</ref><ref>{{cite journal |last1=Serrat |first1=Maria A. |last2=King |first2=Donna |last3=Lovejoy |first3=C. Owen |year=2008 |title=Temperature regulates limb length in homeotherms by directly modulating cartilage growth |journal=[[Proceedings of the National Academy of Sciences]] |volume=105 |issue=49 |pages=19348–19353 |doi=10.1073/pnas.0803319105 |pmid=19047632 |pmc=2614764 |bibcode=2008PNAS..10519348S |url=http://www.pnas.org/content/105/49/19348.full.pdf|doi-access=free }}</ref>

==See also==
* [[Bergmann's rule]], which correlates latitude with body mass in animals
* [[Gloger's rule]], which correlates humidity with pigmentation in animals
* [[Cold and heat adaptations in humans]]
* [[List of eponymous laws]]

==References==
{{reflist|30em}}

{{Biological rules}}

[[Category:Physiology]]
[[Category:Ecogeographic rules]]