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Cetacean intelligence
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===Size=== [[Brain size]] was previously considered a major indicator of the intelligence of an animal. However, many other factors also affect intelligence, and recent discoveries concerning [[bird intelligence]] have called into question the influence of brain size.<ref name="Brain Mass" /> Since most of the brain is used for maintaining bodily functions, greater ratios of brain to body mass may increase the amount of brain mass available for more complex cognitive tasks.<ref name="nasa" /> [[Allometric]] analysis indicates that in general, mammalian brain size scales at approximately the {{frac|2|3}} or {{frac|3|4}} exponent of body mass.<ref name="Allometry" /> Comparison of actual brain size with the size expected from allometry provides an [[encephalization quotient]] (EQ) that can be used as a more accurate indicator of an animal's intelligence. [[File:Preserved sperm whale brain.jpg|right|thumb|Brain of the [[sperm whale]], considered the largest brain in the animal kingdom]] * [[Sperm whale]]s (''Physeter macrocephalus'') have the largest known brain mass of any extant animal, averaging 7.8 kg in mature males.<ref>{{Cite web |title=Sperm Whales (''Physeter macrocephalus'') |url=http://www.nmfs.noaa.gov/pr/species/mammals/cetaceans/spermwhale.htm |access-date=2007-02-09}}</ref> * [[Orcas]] (''Orcinus orca'') have the second largest known brain mass of any extant animal. (5.4-6.8 kg).<ref>[[Brain size]]{{Circular reference|date=November 2017}}</ref> * [[Bottlenose dolphin]]s (''Tursiops truncatus'') have an absolute brain mass of 1,500β1,700 grams. This is slightly greater than that of humans (1,300β1,400 grams) and about four times that of [[Common chimpanzee|chimpanzees]] (400 grams).<ref>{{Cite web |title=Brain facts and figures |url=http://faculty.washington.edu/chudler/facts.html |access-date=2006-10-24}}</ref> * The [[brain to body mass ratio]] (not the encephalization quotient) in some members of the odontocete superfamily Delphinoidea (dolphins, porpoises, belugas, and narwhals) is greater than modern humans, and greater than all other mammals (there is debate whether that of the [[treeshrew]] might be second in place of humans).<ref>{{Cite web |last=Fields, R. Douglas |date=2008-01-15 |title=Are Whales Smarter than We Are? |url=http://www.scientificamerican.com/blog/post.cfm?id=are-whales-smarter-than-we-are |url-status=dead |archive-url=https://web.archive.org/web/20100727161600/http://www.scientificamerican.com/blog/post.cfm?id=are-whales-smarter-than-we-are |archive-date=July 27, 2010 |access-date=2010-10-13 |website=Mind Matters |publisher=Scientific American Community}}</ref><ref>"Origin and evolution of large brains in toothed whales", Lori Marino1,Daniel W. McShea2, Mark D. Uhen, The Anatomoical Record, 20 OCT 2004</ref> In some dolphins, it is less than half that of humans: 0.9% versus 2.1%.{{Citation needed|date=December 2010}} However, this comparison is complicated by the large amount of insulating [[blubber]] Delphinoidea brains have (15-20% of mass). * The [[encephalization quotient]] (EQ) varies widely between species. The [[northern right whale dolphin]] has an EQ of approximately 5.55; the [[common bottlenose dolphin]] of 5.26;<ref>{{cite journal |last=Osvaldo |first=Cairo |title=External Measures of Cognition |journal=Frontiers in Human Neuroscience |volume=5 |issue=108 |date=2011-10-04 |page=108 |doi= 10.3389/fnhum.2011.00108 |pmid=22065955 |pmc=3207484 |quote=Table 1 |doi-access=free }}</ref> the [[tucuxi dolphin]] of 4.56; the [[orca]] of 2.57; the [[pygmy sperm whales]] of 1.78; the [[narwhals]] of 1.76; the [[La Plata dolphin]] of 1.67; the [[Ganges river dolphin]] of 1.55; the [[sperm whales]] of 0.58;<ref name=Marino/> the [[dwarf sperm whale]] of 1.63; the [[beluga whales]] of 2.24; the [[false killer whale]] of 4.03; the [[amazon river dolphin]] of 2.51; the [[cuvier's beaked whale]] of 0.92; the [[harbour porpoise]] of 2.95; the [[dall's porpoise]] of 3.54;<ref>{{cite web |last1=L|first1=Marino|title=Cetacean brains: How aquatic are they?|page=696|url=https://www.wellbeingintlstudiesrepository.org/cgi/viewcontent.cgi?article=1006&context=anatom|access-date=26 February 2025}}</ref> and the [[blue whales]] of 0.19.<ref>{{cite web |title=Are Blue Whales Intelligent? Cetacean Intelligence|url=https://natureweb.co/are-blue-whales-intelligent/|date=28 December 2022|access-date=17 February 2025}}</ref> In comparison to other animals, [[elephants]] have an EQ ranging from 1.13 to 2.36;<ref name="Shoshani 124β157">{{Cite journal |last1=Shoshani |first1=Jeheskel |last2=Kupsky |first2=William J. |last3=Marchant |first3=Gary H. |date=30 June 2006 |title=Elephant brain Part I: Gross morphology, functions,comparative anatomy, and evolution |journal=Brain Research Bulletin |volume=70 |issue=2 |pages=124β157 |doi=10.1016/j.brainresbull.2006.03.016 |pmid=16782503 |s2cid=14339772}}</ref>{{rp|151}} [[Common chimpanzee|chimpanzees]] of approximately 2.49; dogs of 1.17; cats of 1.00; and mice of 0.50.<ref>{{Cite web |title=Thinking about Brain Size |url=http://serendip.brynmawr.edu/bb/kinser/Int3.html |url-status=dead |archive-url=https://web.archive.org/web/20120509185120/http://serendip.brynmawr.edu/bb/kinser/Int3.html |archive-date=2012-05-09 |access-date=2007-02-09}}</ref> Sperm whale, Blue whale, and [[Humpback whale]] (EQ .18) are not thought to be exceptionally unintelligent, although they have very low EQs.<ref>{{cite web |title=Brain EQ (Encephalization Quotient) - Aquatic Ape Theory|url=https://www.aquaticape.org/eq.html|access-date=22 February 2025}}</ref> * The majority of [[mammals]] are born with a brain close to 90% of the adult brain weight.<ref name="Poole" /> Humans are born with 28%<ref name=Poole/> of the adult brain weight, [[Common chimpanzee|chimpanzee]]s with 54%,<ref name=Poole/> [[bottlenose dolphins]] with 42.5%,<ref name="DolphinWindow" /> and [[elephants]] with 35%.<ref name="ElephantBrainSize" /> [[Spindle neuron|Spindle cells]] (neurons without extensive branching) have been discovered in the brains of the [[humpback whale]], [[fin whale]], [[sperm whale]], orca,<ref name="Whale Brain" /><ref name="Hof" /> [[bottlenose dolphin]]s, [[Risso's dolphin]]s, and [[beluga whale]]s.<ref name="Butti" /> Humans, great apes, and elephants, species all well known for their high intelligence, are the only others known to have spindle cells.<ref name="Elephant Brain" />{{rp|page=242}} Spindle neurons appear to play a central role in the development of intelligent behavior. Such a discovery may suggest a [[convergent evolution]] of these species.<ref name="Elephant Brain 2" />
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