Editing Encephalization quotient (section)

==EQ and intelligence in mammals==
Intelligence in animals is hard to establish, but the larger the brain is relative to the body, the more brain weight might be available for more complex [[cognitive]] tasks. The EQ formula, as opposed to the method of simply measuring raw brain weight or brain weight to body weight, makes for a ranking of animals that coincides better with observed complexity of behaviour. A primary reason for the use of EQ instead of a simple brain to body mass ratio is that smaller animals tend to have a higher proportional brain mass, but do not show the same indications of higher cognition as animals with a high EQ.<ref name="Cairo O. 2011 108">{{cite journal |author=Cairo O. |title=External measures of cognition |journal=Frontiers in Human Neuroscience |volume=5 |pages=108 |doi=10.3389/fnhum.2011.00108 |pmid=22065955 |pmc=3207484 |year=2011 |doi-access=free }}</ref>

=== Grey floor ===
The driving theorization behind the development of EQ is that an animal of a certain size requires a minimum number of neurons for basic functioning, sometimes referred to as a grey floor. There is also a limit to how large an animal's brain can grow given its body size – due to limitations like gestation period, energetics, and the need to physically support the encephalized region throughout maturation. When normalizing a standard brain size for a group of animals, a slope can be determined to show what a species' expected brain to body mass ratio would be. Species with brain to body mass ratios below this standard are nearing the grey floor, and do not need extra grey matter. Species which fall above this standard have more grey matter than is necessary for basic functions. Presumably these extra neurons are used for higher cognitive processes.<ref name="Dunbar R.I. 2007 1344–1347">{{citation |author=Dunbar R.I. |title=Evolution in the social brain |journal=Science |volume=317 |issue=5843 |pages=1344–1347 |publisher=science magazine |bibcode=2007Sci...317.1344D |year=2007 |doi=10.1126/science.1145463 |pmid=17823343 |s2cid=1516792 }}</ref>

=== Taxonomic trends ===
Mean EQ for mammals is around 1, with [[carnivora]]ns, [[cetacea]]ns and [[primates]] above 1, and [[insectivores]] and [[herbivore]]s below. Large mammals tend to have the highest EQs of all animals, while small mammals and avians have similar EQs.<ref name="Dunbar R.I. 2007 1344–1347"/> This reflects two major trends. One is that brain matter is extremely costly in terms of energy needed to sustain it.<ref>{{cite journal |last=Isler |first=K. |author2=van Schaik |author3=C. P  |title=Metabolic costs of brain size evolution |journal=Biology Letters |date=22 December 2006 |volume=2 |issue=4 |pages=557–560 |doi=10.1098/rsbl.2006.0538 |pmid=17148287 |pmc=1834002}}</ref> Animals with nutrient rich diets tend to have higher EQs, which is necessary for the energetically costly tissue of brain matter. Not only is it metabolically demanding to grow throughout embryonic and postnatal development, it is costly to maintain as well.

Arguments have been made that some carnivores may have higher EQ's due to their relatively enriched diets, as well as the cognitive capacity required for effectively hunting prey.<ref>{{cite journal |last=Savage |first=J.G. |title=Evolution in carnivorous mammals |journal=Palaeontology |year=1977 |volume=20 |issue=2 |pages=237–271 |url=https://www.palass.org/publications/palaeontology-journal/archive/20/2/article_pp237-271 }}</ref><ref>{{cite journal |last1=Lefebvre |first1=Louis |last2=Reader |first2=Simon M. |last3=Sol |first3=Daniel |title=Brains, Innovations and Evolution in Birds and Primates |journal=Brain, Behavior and Evolution |date=2004 |volume=63 |issue=4 |pages=233–246 |doi=10.1159/000076784 |pmid=15084816 |doi-access=free }}</ref> One example of this is brain size of a [[wolf]]; about 30% larger than a similarly sized domestic dog, potentially derivative of different needs in their respective way of life.<ref>{{cite news |title=Why Brain Size Doesn't Correlate With Intelligence |url=https://www.smithsonianmag.com/science-nature/why-brain-size-doesnt-correlate-with-intelligence-180947627/ |work=Smithsonian Magazine }}</ref>

=== Dietary trends ===
Of the animals demonstrating the highest EQ's (see associated table), many are primarily [[frugivore]]s, including [[apes]], [[macaque]]s, and [[proboscidea]]ns. This dietary categorization is significant to inferring the pressures which drive higher EQ's. Specifically, frugivores must utilize a complex, trichromatic map of visual space to locate and pick ripe fruits and are able to provide for the high energetic demands of increased brain mass.<ref name=DecasienPrimate>{{cite journal |last1=DeCasien |first1=Alex R. |last2=Williams |first2=Scott A. |last3=Higham |first3=James P. |title=Primate brain size is predicted by diet but not sociality |journal=Nature Ecology & Evolution |date=27 March 2017 |volume=1 |issue=5 |pages=112 |doi=10.1038/s41559-017-0112 |pmid=28812699 |bibcode=2017NatEE...1..112D |s2cid=205564046 }}</ref>

[[Trophic level]]—"height" on the [[food chain]]—is yet another factor that has been correlated with EQ in mammals. [[Eutheria]] with either high AB (absolute brain-mass) or high EQ occupy positions at high trophic levels. Eutheria low on the network of food chains can only develop a high RB (relative brain-mass) so long as they have small body masses.<ref name=Steinhausen2016>{{cite journal |last1=Steinhausen |first1=Charlene |last2=Zehl |first2=Lyuba |last3=Haas-Rioth |first3=Michaela |last4=Morcinek |first4=Kerstin |last5=Walkowiak |first5=Wolfgang |last6=Huggenberger |first6=Stefan |title=Multivariate Meta-Analysis of Brain-Mass Correlations in Eutherian Mammals |journal=Frontiers in Neuroanatomy |date=30 September 2016 |volume=10 |pages=91 |doi=10.3389/fnana.2016.00091 |pmid=27746724 |pmc=5043137 |doi-access=free }}</ref> This presents an interesting conundrum for intelligent small animals, who have behaviors radically different from intelligent large animals. 

According to Steinhausen ''et al''.(2016): <blockquote>Animals with high RB [relative brain-mass] usually have (1)&nbsp;a short life span, (2)&nbsp;reach sexual maturity early, and (3)&nbsp;have short and frequent gestations. Moreover, males of species with high RB also have few potential sexual partners. In contrast, animals with high EQs have (1)&nbsp;a high number of potential sexual partners, (2)&nbsp;delayed sexual maturity, and (3)&nbsp;rare gestations with small litter sizes.<ref name=Steinhausen2016/></blockquote>

=== Sociality ===
Another factor previously thought to have great impact on brain size is sociality and flock size.<ref>{{cite journal |doi=10.1098/rspb.2005.3283 |title=Both social and ecological factors predict ungulate brain size |first1=Susanne |last1=Shultz |first2=R.I.M. |last2=Dunbar |volume=273 |issue=1583 |journal=Proceedings of the Royal Society B: Biological Sciences |pages=207–215 |pmid=16555789 |pmc=1560022 |year=2006}}</ref> This was a long-standing theory until the correlation between frugivory and EQ was shown to be more statistically significant. While no longer the predominant inference as to selection pressure for high EQ, the social brain hypothesis still has some support.<ref name=DecasienPrimate/> For example, dogs (a social species) have a higher EQ than cats (a mostly solitary species). Animals with very large flock size and/or complex social systems consistently score high EQ, with [[dolphin]]s and [[orca]]s having the highest EQ of all [[cetaceans]],<ref name="Marino2006">{{cite journal|last1=Marino|first1=Lori|last2=Sol|first2=Daniel|last3=Toren|first3=Kristen|last4=Lefebvre|first4=Louis|date=April 2006|title=Does diving limit brain size in cetaceans?|url=https://animalstudiesrepository.org/cgi/viewcontent.cgi?article=1011&context=acwp_vsm|journal=Marine Mammal Science|volume=22|issue=2|pages=413–425|doi=10.1111/j.1748-7692.2006.00042.x|bibcode=2006MMamS..22..413M |s2cid=14898849 |url-access=subscription}}</ref> and humans with their extremely large societies and complex social life topping the list by a good margin.<ref name="Roth2005" />