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Brain–body mass ratio
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<h2 id="brainbody-size-relationship">Brain–body size relationship</h2> <p><a href="/facts/Brain_size/K0xy5XT5">Brain size</a> usually increases with body size in animals (i.e. large animals usually have larger brains than smaller animals);<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> the relationship is not, however, linear. Small mammals such as <a href="/facts/Mice/6m1X7m0g">mice</a> may have a brain/body ratio similar to humans, while elephants have a comparatively lower brain/body ratio.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a><a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> </p><p>In animals, it is thought that the larger the brain, the more brain weight will be available for more complex cognitive tasks. However, large animals need more neurons to represent their own bodies and control specific muscles; thus, relative rather than absolute brain size makes for a ranking of animals that better coincides with the observed complexity of animal behaviour. The relationship between brain-to-body mass ratio and complexity of behaviour is not perfect as other factors also influence intelligence, like the evolution of the recent <a href="/facts/Cerebral_cortex/GpXosGHP">cerebral cortex</a> and different degrees of brain folding,<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> which increase the surface of the cortex, which is <a href="/facts/Correlation/egkluAEm">positively correlated</a> in humans to intelligence. The noted exception to this, of course, is swelling of the brain which, while resulting in greater surface area, does not alter the intelligence of those suffering from it.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> </p> <h3>Relation to metabolism</h3> <p>The relationship between brain weight and body weight of all living vertebrates follows two completely separate linear functions for <a href="/facts/Thermoregulation/V692hIjw">cold-blooded and warm-blooded</a> animals.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> Cold-blooded vertebrates have much smaller brains than warm-blooded vertebrates of the same size. However, if <a href="/facts/Brain/EKla9NkJ">brain metabolism</a> is taken into account, the brain-to-body relationship of both warm and cold-blooded vertebrates becomes similar, with most using between 2 and 8 percent of their basal metabolism for the brain and spinal cord.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> </p> <h2 id="comparisons-between-groups">Comparisons between groups</h2> <table><tbody><tr><th>Species</th><th>Brain:bodymass ratio (E:S)<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a></th></tr><tr><td>Small ants</td><td>1:7<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a></td></tr><tr><td>Tree shrew</td><td>1:10</td></tr><tr><td>Small birds</td><td>1:12</td></tr><tr><td>Elephantfish</td><td>1:32</td></tr><tr><td>Mouse</td><td>1:40</td></tr><tr><td>Human</td><td>1:40</td></tr><tr><td>Cat</td><td>1:100</td></tr><tr><td>Dog</td><td>1:125</td></tr><tr><td>Frog</td><td>1:172</td></tr><tr><td>Lion</td><td>1:550</td></tr><tr><td>Elephant</td><td>1:560</td></tr><tr><td>Horse</td><td>1:600</td></tr><tr><td>Shark</td><td>1:2496</td></tr><tr><td>Hippopotamus</td><td>1:2789</td></tr></tbody></table> <p class="note">See also: <a href="/facts/Cetacean_intelligence/c3hsvFVj">Cetacean intelligence § Brain size</a></p> <p><a href="/facts/Dolphin/NUxUP7Ph">Dolphins</a> have the highest brain-to-body weight ratio of all <a href="/facts/Cetaceans/rtC33h63">cetaceans</a>.<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> <a href="/facts/Monitor_lizard/QThU3SvH">Monitor lizards</a>, <a href="/facts/Tegu/4dHDchCN">tegus</a> and <a href="/facts/Anole/D0nh96tW">anoles</a> and some <a href="/facts/Tortoise/XWKByUCz">tortoise</a> species have the largest among reptiles. Among birds, the highest brain-to-body ratios are found among <a href="/facts/Parrot/u32QQjMe">parrots</a>, <a href="/facts/Crow/S8n67ojy">crows</a>, <a href="/facts/Magpie/uNee6IsV">magpies</a>, <a href="/facts/Jay/WwJpVWTx">jays</a> and <a href="/facts/Raven/RMSymMox">ravens</a>. Among amphibians, the studies are still limited. Either <a href="/facts/Octopus/z5uokKFF">octopuses</a><a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a> or <a href="/facts/Jumping_spider/gjlule5d">jumping spiders</a><a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a> have some of the highest for an <a href="/facts/Invertebrate/3CyqCVnN">invertebrate</a>, although some <a href="/facts/Ant/CyxckAAE">ant</a> species have 14–15% of their mass in their brains, the highest value known for any animal. <a href="/facts/Shark/rh5Cotvx">Sharks</a> have one of the highest for <a href="/facts/Fish/fln4gH9V">fish</a> alongside <a href="/facts/Manta_ray/SqX69Gwj">manta rays</a> (although the electrogenic <a href="/facts/Mormyridae/yKbL7X3n">elephantfish</a> has a ratio nearly 80 times higher—about 1/32, which is slightly higher than that for humans).<a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a> <a href="/facts/Treeshrew/e3J7FEjn">Treeshrews</a> have a higher brain to body mass ratio than any other mammal, including <a href="/facts/Human/rlcTENsr">humans</a>.<a class="footnote-ref" id="fnref:16" href="#fn:16"><sup>16</sup></a> Treeshrews hold about 10% of their body mass in their brain.<a class="footnote-ref" id="fnref:17" href="#fn:17"><sup>17</sup></a> </p><p>Generally speaking, the larger the animal, the smaller the brain-to-body mass ratio is. Thus, large <a href="/facts/Whale/EMJBgXfb">whales</a> have very small brains compared to their weight, and small <a href="/facts/Rodent/mT4m8QJq">rodents</a> like <a href="/facts/Mouse/6m1X7m0g">mice</a> have a relatively large brain, giving a brain-to-body mass ratio similar to humans.<a class="footnote-ref" id="fnref:18" href="#fn:18"><sup>18</sup></a> One explanation could be that as an animal's brain gets larger, the size of the neural cells remains the same, and more nerve cells will cause the brain to increase in size to a lesser degree than the rest of the body. This phenomenon can be described by an equation of the form <i>E = CSr</i>, where <i>E</i> and <i>S</i> are brain and body weights, <i>r</i> a constant that depends on animal family (but close to 2/3 in many vertebrates<a class="footnote-ref" id="fnref:19" href="#fn:19"><sup>19</sup></a>), and <i>C</i> is the cephalization factor.<a class="footnote-ref" id="fnref:20" href="#fn:20"><sup>20</sup></a> </p><p>It has been argued that the animal's <a href="/facts/Ecological_niche/YnhNkL2e">ecological niche</a>, rather than its evolutionary family, is the main determinant of its encephalization factor <i>C</i>.<a class="footnote-ref" id="fnref:21" href="#fn:21"><sup>21</sup></a> In the essay "Bligh's Bounty",<a class="footnote-ref" id="fnref:22" href="#fn:22"><sup>22</sup></a> <a href="/facts/Stephen_Jay_Gould/FtAcabjg">Stephen Jay Gould</a> noted that if one looks at vertebrates with very low encephalization quotient, their brains are slightly less massive than their spinal cords. Theoretically, intelligence might correlate with the absolute amount of brain an animal has after subtracting the weight of the spinal cord from the brain. This formula is useless for invertebrates because they do not have spinal cords, or in some cases, central nervous systems. </p> <h2 id="criticism">Criticism</h2> <p>Recent research indicates that, in non-human primates, whole <a href="/facts/Brain_size/K0xy5XT5">brain size</a> is a better measure of cognitive abilities than brain-to-body mass ratio. The total weight of the species is greater than the predicted sample only if the frontal lobe is adjusted for spatial relation.<a class="footnote-ref" id="fnref:23" href="#fn:23"><sup>23</sup></a> The brain-to-body mass ratio was however found to be an excellent predictor of variation in problem solving abilities among <a href="/facts/Carnivora/4wWDW8RY">carnivoran mammals</a>.<a class="footnote-ref" id="fnref:24" href="#fn:24"><sup>24</sup></a> </p><p>In humans, the brain to body weight ratio can vary greatly from person to person; it would be much higher in an underweight person than an overweight person, and higher in infants than adults. The same problem is encountered when dealing with marine mammals, which may have considerable body fat masses. Some researchers therefore prefer lean body weight to brain mass as a better predictor.<a class="footnote-ref" id="fnref:25" href="#fn:25"><sup>25</sup></a> </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Cranial_capacity/K0xy5XT5">Cranial capacity</a></li> <li><a href="/facts/Craniometry/aGRGRctC">Craniometry</a></li> <li><a href="/facts/Encephalization_quotient/tw7CzCSm">Encephalization quotient</a></li> <li><a href="/facts/List_of_animals_by_number_of_neurons/EWIkYXeK">List of animals by number of neurons</a></li> <li><a href="/facts/Phrenology/Te2TYuQA">Phrenology</a></li> <li><a href="/facts/Schauenberg%27s_index/KXbYVWJw">Schauenberg's index</a></li></ul> <h2 id="external-links">External links</h2> <ul><li><a href="https://web.archive.org/web/20050325105538/http://www.wsu.edu/~taflinge/mindwork/mawint1.html">https://web.archive.org/web/20050325105538/http://www.wsu.edu/~taflinge/mindwork/mawint1.html</a></li> <li><a href="http://brainmuseum.org/evolution/paleo/index.html">A graph of body mass vs. brain mass</a></li> <li><a href="https://web.archive.org/web/20010709234346/http://yoyo.cc.monash.edu.au/~tzvi/GOULD.html">"Bligh's Bounty"</a> — <a href="/facts/Stephen_Jay_Gould/FtAcabjg">Stephen Jay Gould</a></li> <li><a href="http://www.ted.com/talks/suzana_herculano_houzel_what_is_so_special_about_the_human_brain.html">Suzana Herculano Houzel: What is so special about the human brain</a> <a href="https://web.archive.org/web/20140226153003/http://www.ted.com/talks/suzana_herculano_houzel_what_is_so_special_about_the_human_brain.html">Archived</a> 2014-02-26 at the <a href="/facts/Wayback_Machine/nmQ3a6JC">Wayback Machine</a> <a href="/facts/TED_(conference)/Sc3JxnA1">TED</a> talk, June 2013.</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>"Development of Intelligence". Ircamera.as.arizona.edu. Archived from the original on 2014-12-31. Retrieved 2011-05-12. <a href="https://web.archive.org/web/20141231070052/http://ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/intelligence.htm" target="_blank">https://web.archive.org/web/20141231070052/http://ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/intelligence.htm</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Cairό, O (2011). "External measures of cognition". Front Hum Neurosci. 5: 108. doi:10.3389/fnhum.2011.00108. PMC 3207484. PMID 22065955. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3207484" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3207484</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>"Brain and Body Size... and Intelligence". SerendipStudio.org. 2003-03-07. Retrieved 2019-02-24. <a href="https://serendipstudio.org/bb/kinser/Int3.html" target="_blank">https://serendipstudio.org/bb/kinser/Int3.html</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>"Brain and Body Size... and Intelligence". SerendipStudio.org. 2003-03-07. Retrieved 2019-02-24. <a href="https://serendipstudio.org/bb/kinser/Int3.html" target="_blank">https://serendipstudio.org/bb/kinser/Int3.html</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Hart, B. L.; Hart, L. A.; McCoy, M.; Sarath, C. R. (November 2001). "Cognitive behaviour in Asian elephants: use and modification of branches for fly switching". Animal Behaviour. 62 (5): 839–847. doi:10.1006/anbe.2001.1815. S2CID 53184282. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>"Cortical Folding and Intelligence". Retrieved 2008-09-15. <a href="https://serendipstudio.org/bb/kinser/Int4.html" target="_blank">https://serendipstudio.org/bb/kinser/Int4.html</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>Haier, R.J.; Jung, R.E.; Yeo, R.C.; Head, K.; Alkired, M.T. (2004). "Structural brain variation and general intelligence". NeuroImage. 23 (1): 425–433. doi:10.1016/j.neuroimage.2004.04.025. PMID 15325390. S2CID 29426973. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>A graph of the relation between brain weight and body weight of living vertebrates Retrieved 10 February 2018. <a href="http://brainmuseum.org/evolution/paleo/index.html" target="_blank">http://brainmuseum.org/evolution/paleo/index.html</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>A graph of the relation of CNS to body metabolism in vertebrates Retrieved 10 February 2018. <a href="http://culture-of-peace.info/brain/Relation_of_CNS_to_Body_Metabolism.png" target="_blank">http://culture-of-peace.info/brain/Relation_of_CNS_to_Body_Metabolism.png</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>"Brain and Body Size... and Intelligence". SerendipStudio.org. 2003-03-07. 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