HOME

TheInfoList



OR:

Encephalization quotient (EQ), encephalization level (EL), or just encephalization is a relative
brain size The size of the brain is a frequent topic of study within the fields of anatomy, biological anthropology, animal science and evolution. Brain size is sometimes measured by weight and sometimes by volume (via MRI scans or by skull volume). Neur ...
measure that is defined as the ratio between observed to predicted brain mass for an animal of a given size, based on
nonlinear regression In statistics, nonlinear regression is a form of regression analysis in which observational data are modeled by a function which is a nonlinear combination of the model parameters and depends on one or more independent variables. The data are fit ...
on a range of reference species. It has been used as a proxy for intelligence and thus as a possible way of comparing the intelligences of different
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
. For this purpose it is a more refined measurement than the raw brain-to-body mass ratio, as it takes into account
allometric Allometry is the study of the relationship of body size to shape, anatomy, physiology and finally behaviour, first outlined by Otto Snell in 1892, by D'Arcy Thompson in 1917 in ''On Growth and Form'' and by Julian Huxley in 1932. Overview Allome ...
effects. Expressed as a formula, the relationship has been developed for
mammals Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
and may not yield relevant results when applied outside this group.


Perspective on intelligence measures

Encephalization quotient was developed in an attempt to provide a way of correlating an animal's physical characteristics with perceived intelligence. It improved on the previous attempt, brain-to-body mass ratio, so it has persisted. Subsequent work, notably Roth, found EQ to be flawed and suggested brain size was a better predictor, but that has problems as well. Currently the best predictor for intelligence across all animals is
forebrain In the anatomy of the brain of vertebrates, the forebrain or prosencephalon is the Anatomical terms of location#Directional terms, rostral (forward-most) portion of the brain. The forebrain (prosencephalon), the midbrain (mesencephalon), and hin ...
neuron count. This was not seen earlier because neuron counts were previously inaccurate for most animals. For example, human brain neuron count was given as 100 billion for decades before Herculano-Houzel found a more reliable method of counting brain cells. It could have been anticipated that EQ might be superseded because of both the number of exceptions and the growing complexity of the formulae it used. (See the rest of this article.) The simplicity of counting neurons has replaced it. The concept in EQ of comparing the brain capacity exceeding that required for body sense and motor activity may yet live on to provide an even better prediction of intelligence, but that work has not been done yet.


Variance in brain sizes

Body size accounts for 80–90% of the variance in brain size, between species, and a relationship described by an allometric equation: the regression of the logarithms of brain size on body size. The distance of a species from the regression line is a measure of its encephalization. The scales are logarithmic, distance, or residual, is an encephalization quotient (EQ), the ratio of actual brain size to expected brain size. Encephalization is a characteristic of a species. Rules for brain size relates to the number brain neurons have varied in evolution, then not all mammalian brains are necessarily built as larger or smaller versions of a same plan, with proportionately larger or smaller numbers of neurons. Similarly sized brains, such as a cow or chimpanzee, might in that scenario contain very different numbers of neurons, just as a very large cetacean brain might contain fewer neurons than a gorilla brain. Size comparison between the human brain and non-primate brains, larger or smaller, might simply be inadequate and uninformative – and our view of the human brain as outlier, a special oddity, may have been based on the mistaken assumption that all brains are made the same (Herculano-Houzel, 2012).


Limitations and possible improvements over EQ

There is a distinction between brain parts that are necessary for the maintenance of the body and those that are associated with improved cognitive functions. These brain parts, although functionally different, all contribute to the overall weight of the brain. Jerison (1973) for this reason, has considered 'extra neurons', neurons that contribute strictly to cognitive capacities, as more important indicators of intelligence than pure EQ. Gibson et al. (2001) reasoned that bigger brains generally contain more 'extra neurons' and thus are better predictors of cognitive abilities than pure EQ, among primates. Factors such as the recent evolution of the
cerebral cortex The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consisting of ...
and different degrees of brain folding (
gyrification Gyrification is the process of forming the characteristic folds of the cerebral cortex. The peak of such a fold is called a ''gyrus'' (pl. ''gyri''), and its trough is called a '' sulcus'' (pl. ''sulci''). The neurons of the cerebral cortex re ...
), which increases the surface area (and volume) of the cortex, are positively correlated to intelligence in humans. In a meta-analysis, Deaner et al. (2007) tested ABS, cortex size, cortex-to-brain ratio, EQ, and corrected relative brain size (cRBS) against global cognitive capacities. They have found that, after normalization, only ABS and neocortex size showed significant correlation to cognitive abilities. In primates, ABS, neocortex size, and Nc (the number of cortical neurons) correlated fairly well with cognitive abilities. However, there were inconsistencies found for Nc. According to the authors, these inconsistencies were the result of the faulty assumption that Nc increases linearly with the size of the cortical surface. This notion is incorrect because the assumption does not take into account the variability in cortical thickness and cortical neuron density, which should influence Nc. According to Cairo (2011), EQ has flaws to its design when considering individual data points rather than a species as a whole. It is inherently biased given that the cranial volume of an obese and underweight individual would be roughly similar, but their body masses would be drastically different. Another difference of this nature is a lack of accounting for sexual dimorphism. For example, the female human generally has smaller cranial volume than the male, however this does not mean that a female and male of the same body mass would have different cognitive abilities. Considering all of these flaws, EQ should be a metric for interspecies comparison only, not for intraspecies comparison. The notion that encephalization quotient corresponds to intelligence has been disputed by Roth and Dicke (2012). They consider the absolute number of cortical neurons and neural connections as better correlates of cognitive ability. According to Roth and Dicke (2012), mammals with relatively high cortex volume and neuron packing density (NPD) are more intelligent than mammals with the same brain size. The human brain stands out from the rest of the mammalian and vertebrate
taxa In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...
because of its large cortical volume and high NPD,
conduction velocity In neuroscience, nerve conduction velocity (CV) is an important aspect of nerve conduction studies. It is the speed at which an electrochemical impulse propagates down a neural pathway. Conduction velocities are affected by a wide array of factor ...
, and cortical parcellation. All aspects of human intelligence are found, at least in its primitive form, in other nonhuman primates, mammals, or vertebrates, with the exception of syntactical language. Roth and Dicke consider syntactical language an "intelligence amplifier".


Brain-body size relationship

Brain size usually increases with body size in animals (is positively correlated), i.e. large animals usually have larger brains than smaller animals. The relationship is not linear, however. Generally, small mammals have relatively larger brains than big ones.
Mice A mouse ( : mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus musculus' ...
have a direct brain/body size ratio similar to humans (), while
elephant Elephants are the largest existing land animals. Three living species are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant. They are the only surviving members of the family Elephantidae an ...
s have a comparatively small brain/body size (), despite being quite intelligent animals. Several reasons for this trend are possible, one of which is that
neural cells In Biology, biology, the nervous system is the Complex system, highly complex part of an animal that coordinates its Behavior, actions and Sense, sensory information by transmitting action potential, signals to and from different parts of its ...
have a relative constant size. Some brain functions, like the brain pathway responsible for a basic task like drawing breath, are basically similar in a mouse and an elephant. Thus, the same amount of brain matter can govern breathing in a large or a small body. While not all control functions are independent of body size, some are, and hence large animals need comparatively less brain than small animals. This phenomenon can be described by an equation: ''C'' = ''E'' / ''S2/3'' , where ''E'' and ''S'' are brain and body weights respectively, and ''C'' is called the cephalization factor. To determine the value of this factor, the brain- and body-weights of various mammals were plotted against each other, and the curve of ''E'' = ''C'' × ''S''2/3 chosen as the best fit to that data. The cephalization factor and the subsequent encephalization quotient was developed by H.J. Jerison in the late 1960s. The formula for the curve varies, but an empirical fitting of the formula to a sample of mammals gives = 0.12 . As this formula is based on data from mammals, it should be applied to other animals with caution. For some of the other
vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...
classes the power of rather than is sometimes used, and for many groups of
invertebrates Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...
the formula may give no meaningful results at all.


Calculation

Snell's equation of simple
allometry Allometry is the study of the relationship of body size to shape, anatomy, physiology and finally behaviour, first outlined by Otto Snell in 1892, by D'Arcy Thompson in 1917 in ''On Growth and Form'' and by Julian Huxley in 1932. Overview Allom ...
is: :E=CS^r Here "E" is the weight of the brain, "C" is the
cephalization Cephalization is an evolutionary trend in which, over many generations, the mouth, sense organs, and nerve ganglia become concentrated at the front end of an animal, producing a head region. This is associated with movement and bilateral symmetry, ...
factor and "S" is body weight and "r" is the exponential constant. The "encephalization quotient" (EQ) is the coefficient "C" in Snell's allometry equation, usually normalized with respect to a reference species. In the following table, the coefficients have been normalized with respect to the value for the cat, which is therefore attributed an EQ of 1. Another way to calculate encephalization quotient is by dividing the actual weight of an animal's brain with its predicted weight according to Jerison's formula. This measurement of approximate intelligence is more accurate for mammals than for other classes and phyla of
Animalia Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage in ...
.


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 Cognition refers to "the mental action or process of acquiring knowledge and understanding through thought, experience, and the senses". It encompasses all aspects of intellectual functions and processes such as: perception, attention, thought, ...
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.


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.


Taxonomic trends

Mean EQ for mammals is around 1, with
carnivora Carnivora is a Clade, monophyletic order of Placentalia, placental mammals consisting of the most recent common ancestor of all felidae, cat-like and canidae, dog-like animals, and all descendants of that ancestor. Members of this group are f ...
ns,
cetacea Cetacea (; , ) is an infraorder of aquatic mammals that includes whales, dolphins, and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively carnivorous diet. They propel them ...
ns and
primates Primates are a diverse order of mammals. They are divided into the strepsirrhines, which include the lemurs, galagos, and lorisids, and the haplorhines, which include the tarsiers and the simians (monkeys and apes, the latter including huma ...
above 1, and
insectivores A robber fly eating a hoverfly An insectivore is a carnivorous animal or plant that eats insects. An alternative term is entomophage, which can also refer to the human practice of eating insects. The first vertebrate insectivores wer ...
and
herbivore A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...
s below. Large mammals tend to have the highest EQs of all animals, while small mammals and avians have similar EQs. This reflects two major trends. One is that brain matter is extremely costly in terms of energy needed to sustain it. 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. One example of this is brain size of a
wolf The wolf (''Canis lupus''; : wolves), also known as the gray wolf or grey wolf, is a large canine native to Eurasia and North America. More than thirty subspecies of ''Canis lupus'' have been recognized, and gray wolves, as popularly u ...
; about 30% larger than a similarly sized domestic dog, potentially derivative of different needs in their respective way of life.


Dietary trends

It is worth noting, however, that of the animals demonstrating the highest EQ's (see associated table), many are primarily
frugivores A frugivore is an animal that thrives mostly on raw fruits or succulent fruit-like produce of plants such as roots, shoots, nuts and seeds. Approximately 20% of mammalian herbivores eat fruit. Frugivores are highly dependent on the abundance and ...
, including
apes Apes (collectively Hominoidea ) are a clade of Old World simians native to sub-Saharan Africa and Southeast Asia (though they were more widespread in Africa, most of Asia, and as well as Europe in prehistory), which together with its sister g ...
,
macaque The macaques () constitute a genus (''Macaca'') of gregarious Old World monkeys of the subfamily Cercopithecinae. The 23 species of macaques inhabit ranges throughout Asia, North Africa, and (in one instance) Gibraltar. Macaques are principally ...
s, and
proboscidea The Proboscidea (; , ) are a taxonomic order of afrotherian mammals containing one living family (Elephantidae) and several extinct families. First described by J. Illiger in 1811, it encompasses the elephants and their close relatives. From ...
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. Trophic level—"height" on the food chain—is yet another factor that has been correlated with EQ in mammals.
Eutheria Eutheria (; from Greek , 'good, right' and , 'beast'; ) is the clade consisting of all therian mammals that are more closely related to placentals than to marsupials. Eutherians are distinguished from noneutherians by various phenotypic tra ...
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. This presents an interesting conundrum for intelligent small animals, who have behaviors radically different from intelligent large animals. According to Steinhausen ''et al''.(2016):
Animals with high RB
elative brain-mass Elative can refer to: *Elative case, a grammatical case in Finno-Ugric languages and others *Elative (gradation) In Semitic linguistics, the elative ( ar, اِسْمُ تَفْضِيل ', literally meaning "noun of preference") is a stage of g ...
usually have (1) a short life span, (2) reach sexual maturity early, and (3) 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) a high number of potential sexual partners, (2) delayed sexual maturity, and (3) rare gestations with small litter sizes.


Sociality

Another factor previously thought to have great impact on brain size is sociality and flock size. 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. 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 A dolphin is an aquatic mammal within the infraorder Cetacea. Dolphin species belong to the families Delphinidae (the oceanic dolphins), Platanistidae (the Indian river dolphins), Iniidae (the New World river dolphins), Pontoporiidae (the ...
s and
orca The orca or killer whale (''Orcinus orca'') is a toothed whale belonging to the oceanic dolphin family, of which it is the largest member. It is the only Extant taxon, extant species in the genus ''Orcinus'' and is recognizable by its black ...
s having the highest EQ of all
cetaceans Cetacea (; , ) is an infraorder of aquatic mammals that includes whales, dolphins, and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively carnivorous diet. They propel them ...
, and humans with their extremely large societies and complex social life topping the list by a good margin.


Comparisons with non-mammalian animals

Birds generally have lower EQ than mammals, but
parrots Parrots, also known as psittacines (), are birds of the roughly 398 species in 92 genus (biology), genera comprising the order (biology), order Psittaciformes (), found mostly in tropics, tropical and subtropics, subtropical regions. The order ...
and particularly the
corvid Corvidae is a Cosmopolitan distribution, cosmopolitan family (biology), family of oscine passerine birds that contains the crows, ravens, rook (bird), rooks, jackdaws, jays, magpies, treepies, choughs, and nutcracker (bird), nutcrackers. In coll ...
s show remarkable complex behaviour and high learning ability. Their brains are at the high end of the bird spectrum, but low compared to mammals. Bird cell size is on the other hand generally smaller than that of mammals, which may mean more brain cells and hence
synapse In the nervous system, a synapse is a structure that permits a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or to the target effector cell. Synapses are essential to the transmission of nervous impulses from ...
s per volume, allowing for more complex behaviour from a smaller brain. Both
bird intelligence The difficulty of defining or measuring intelligence in non-human animals makes the subject difficult to study scientifically in birds. In general, birds have relatively large brains compared to their head size. The visual and auditory senses are ...
and brain anatomy are however very different from those of mammals, making direct comparison difficult.
Manta ray Manta rays are large rays belonging to the genus ''Mobula'' (formerly its own genus ''Manta''). The larger species, '' M. birostris'', reaches in width, while the smaller, '' M. alfredi'', reaches . Both have triangular Pectoral fin#AnchPect ...
s have the highest EQ among
fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...
, and either
octopus An octopus ( : octopuses or octopodes, see below for variants) is a soft-bodied, eight- limbed mollusc of the order Octopoda (, ). The order consists of some 300 species and is grouped within the class Cephalopoda with squids, cuttle ...
esGould (1977) Ever since Darwin, c7s1 or
jumping spider Jumping spiders are a group of spiders that constitute the family (biology), family Salticidae. As of 2019, this family contained over 600 described genera and over 6,000 described species, making it the largest family of spiders at 13% of all sp ...
s have the highest among
invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...
s. Despite the jumping spider having a huge brain for its size, it is minuscule in absolute terms, and humans have a much higher EQ despite having a lower raw brain-to-body weight ratio. Mean EQs for
reptiles Reptiles, as most commonly defined are the animals in the Class (biology), class Reptilia ( ), a paraphyletic grouping comprising all sauropsid, sauropsids except birds. Living reptiles comprise turtles, crocodilians, Squamata, squamates (lizar ...
are about one tenth of those of mammals. EQ in birds (and estimated EQ in
other Other often refers to: * Other (philosophy), a concept in psychology and philosophy Other or The Other may also refer to: Film and television * ''The Other'' (1913 film), a German silent film directed by Max Mack * ''The Other'' (1930 film), a ...
dinosaurs) generally also falls below that of mammals, possibly due to lower thermoregulation and/or motor control demands. Estimation of brain size in ''
Archaeopteryx ''Archaeopteryx'' (; ), sometimes referred to by its German name, "" ( ''Primeval Bird''), is a genus of bird-like dinosaurs. The name derives from the ancient Greek (''archaīos''), meaning "ancient", and (''ptéryx''), meaning "feather" ...
'' (one of the oldest known ancestors of birds), shows it had an EQ well above the reptilian range, and just below that of living birds. Biologist
Stephen Jay Gould Stephen Jay Gould (; September 10, 1941 – May 20, 2002) was an American paleontologist, evolutionary biologist, and historian of science. He was one of the most influential and widely read authors of popular science of his generation. Gould sp ...
has noted that if one looks at vertebrates with very low encephalization quotients, 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.


EQ in paleoneurology

Behavioral complexity in living animals can to some degree be observed directly, making the predictive power of the encephalization quotient less relevant. It is however central in
paleoneurology Paleoneurobiology is the study of brain evolution by analysis of brain endocasts to determine endocranial traits and volumes. Considered a subdivision of neuroscience, paleoneurobiology combines techniques from other fields of study including pa ...
, where the
endocast An endocast is the internal cast of a hollow object, often referring to the cranial vault in the study of brain development in humans and other organisms. Endocasts can be artificially made for examining the properties of a hollow, inaccessible sp ...
of the brain cavity and estimated body weight of an animal is all one has to work from. The behavior of extinct mammals and
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
s is typically investigated using EQ formulas. Encephalization quotient is also used in estimating evolution of intelligent behavior in human ancestors. This technique can help in mapping the development of behavioral complexities during human evolution. However, this technique is only limited to when there are both cranial and post-cranial remains associated with individual fossils, to allow for brain to body size comparisons. For example, remains of one
Middle Pleistocene The Chibanian, widely known by its previous designation of Middle Pleistocene, is an age in the international geologic timescale or a stage in chronostratigraphy, being a division of the Pleistocene Epoch within the ongoing Quaternary Period. The ...
human fossil from
Jinniushan Jinniushan () is a Middle Pleistocene paleoanthropological site, dating to around 260,000 BP, most famous for its archaic hominin fossils. The site is located near Yingkou, Liaoning, China. Several new species of extinct birds were also discovere ...
province in northern China has allowed scientists to study the relationship between brain and body size using the Encephalization Quotient. Researchers obtained an EQ of 4.150 for the Jinniushan fossil, and then compared this value with preceding Middle Pleistocene estimates of EQ at 3.7770. The difference in EQ estimates has been associated with a rapid increase in encephalization in Middle Pleistocene hominins. Paleo-neurological comparisons between
Neanderthal Neanderthals (, also ''Homo neanderthalensis'' and erroneously ''Homo sapiens neanderthalensis''), also written as Neandertals, are an extinct species or subspecies of archaic humans who lived in Eurasia until about 40,000 years ago. While th ...
s and anatomically modern ''Homo sapiens'' (AMHS) via Encephalization quotient often rely on the use of endocasts, but there are a lot of drawbacks associated with using this method. For example, endocasts do not provide any information regarding the internal organization of the brain. Furthermore, endocasts are often unclear in terms of the preservation of their boundaries, and it becomes hard to measure where exactly a certain structure starts and ends. If endocasts themselves are not reliable, then the value for brain size used to calculate the EQ could also be unreliable. Additionally, previous studies have suggested that Neanderthals have the same encephalization quotient as modern humans, although their post-crania suggests that they weighed more than modern humans. Because EQ relies on values from both postcrania and crania, the margin for error increases in relying on this proxy in paleo-neurology because of the inherent difficulty in obtaining accurate brain and body mass measurements from the fossil record.


EQ of livestock animals

The EQ of livestock farm animals such as the
domestic pig The pig (''Sus domesticus''), often called swine, hog, or domestic pig when distinguishing from other members of the genus '' Sus'', is an omnivorous, domesticated, even-toed, hoofed mammal. It is variously considered a subspecies of ''Sus s ...
may be significantly lower than would suggest for their apparent intelligence. According to Minervini et al (2016) the brain of the domestic pig is a rather small size compared to the mass of the animal. The tremendous increase in body weight imposed by industrial farming significantly influences brain-to-body weight measures, including the EQ. The EQ of the domestic adult pig is just 0.38, yet pigs can use visual information seen in a mirror to find food, show evidence of self-recognition when presented with their reflections and there is evidence suggesting that pigs are as socially complex as many other highly intelligent animals, possibly sharing a number of cognitive capacities related to social complexity.


History

The concept of encephalization has been a key evolutionary trend throughout human evolution, and consequently an important area of study. Over the course of hominin evolution, brain size has seen an overall increase from 400 cm3 to 1400 cm3. Furthermore, the genus ''Homo'' is specifically defined by a significant increase in brain size. The earliest ''Homo'' species were larger in brain size as compared to contemporary ''
Australopithecus ''Australopithecus'' (, ; ) is a genus of early hominins that existed in Africa during the Late Pliocene and Early Pleistocene. The genus ''Homo'' (which includes modern humans) emerged within ''Australopithecus'', as sister to e.g. ''Australopi ...
'' counterparts, with which they co-inhabited parts of Eastern and Southern Africa. Throughout modern history, humans have been fascinated by the large relative size of our brains, trying to connect brain sizes to overall levels of intelligence. Early brain studies were focused in the field of phrenology, which was pioneered by
Franz Joseph Gall Franz Josef Gall (; 9 March 175822 August 1828) was a German neuroanatomist, physiologist, and pioneer in the study of the localization of mental functions in the brain. Claimed as the founder of the pseudoscience of phrenology, Gall was an earl ...
in 1796 and remained a prevalent discipline throughout the early 19th century. Specifically, phrenologists paid attention to the external morphology of the skull, trying to relate certain lumps to corresponding aspects of personality. They further measured physical brain size in order to equate larger brain sizes to greater levels of intelligence. Today, however,
phrenology Phrenology () is a pseudoscience which involves the measurement of bumps on the skull to predict mental traits.Wihe, J. V. (2002). "Science and Pseudoscience: A Primer in Critical Thinking." In ''Encyclopedia of Pseudoscience'', pp. 195–203. C ...
is considered a
pseudoscience Pseudoscience consists of statements, beliefs, or practices that claim to be both scientific and factual but are incompatible with the scientific method. Pseudoscience is often characterized by contradictory, exaggerated or falsifiability, unfa ...
. Among ancient Greek philosophers,
Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of phil ...
in particular believed that after the heart, the brain was the second most important organ of the body. He also focused on the size of the human brain, writing in 335 BCE that "of all the animals, man has the brain largest in proportion to his size." In 1861, French neurologist
Paul Broca Pierre Paul Broca (, also , , ; 28 June 1824 – 9 July 1880) was a French physician, anatomist and anthropologist. He is best known for his research on Broca's area, a region of the frontal lobe that is named after him. Broca's area is involve ...
tried to make a connection between brain size and intelligence. Through observational studies, he noticed that people working in what he deemed to be more complex fields had larger brains than people working in less complex fields. Also, in 1871,
Charles Darwin Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all species of life have descended fr ...
wrote in his book ''
The Descent of Man ''The Descent of Man, and Selection in Relation to Sex'' is a book by English naturalist Charles Darwin, first published in 1871, which applies evolutionary theory to human evolution, and details his theory of sexual selection, a form of biol ...
'': "No one, I presume, doubts that the large proportion which the size of man's brain bears to his body, compared to the same proportion in the gorilla or orang, is closely connected with his mental powers." The concept of quantifying encephalization is also not a recent phenomenon. In 1889,
Sir Francis Galton Sir Francis Galton, FRS FRAI (; 16 February 1822 – 17 January 1911), was an English Victorian era polymath: a statistician, sociologist, psychologist, anthropologist, tropical explorer, geographer, inventor, meteorologist, proto- ...
, through a study on college students, attempted to quantify the relationship between brain size and intelligence. Due to
Hitler's Adolf Hitler (; 20 April 188930 April 1945) was an Austrian-born German politician who was dictator of Nazi Germany, Germany from 1933 until Death of Adolf Hitler, his death in 1945. Adolf Hitler's rise to power, He rose to power as the le ...
racial policies during
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
, studies on brain size and intelligence temporarily gained a negative reputation. However, with the advent of imaging techniques such as the
fMRI Functional magnetic resonance imaging or functional MRI (fMRI) measures brain activity by detecting changes associated with blood flow. This technique relies on the fact that cerebral blood flow and neuronal activation are coupled. When an area o ...
and
PET scan Positron emission tomography (PET) is a functional imaging technique that uses radioactive substances known as radiotracers to visualize and measure changes in metabolic processes, and in other physiological activities including blood flow, r ...
, several scientific studies were launched to suggest a relationship between encephalization and advanced cognitive abilities. Harry J. Jerison, who invented the formula for encephalization quotient, believed that brain size was proportional to the ability of humans to process information. With this belief, a higher level of encephalization equated to a higher ability to process information. A larger brain could mean a number of different things, including a larger cerebral cortex, a greater number of neuronal associations, or a greater number of neurons overall.


See also

* Brain-to-body mass ratio *
Brain development timelines These are timelines of brain development events in different animal species. *Mouse brain development timeline * Macaque brain development timeline *Human brain development timeline See also * Encephalization quotient * Evolution of the brain * N ...
*
Cephalization Cephalization is an evolutionary trend in which, over many generations, the mouth, sense organs, and nerve ganglia become concentrated at the front end of an animal, producing a head region. This is associated with movement and bilateral symmetry, ...
*
Cranial capacity The size of the brain is a frequent topic of study within the fields of anatomy, biological anthropology, animal science and evolution. Brain size is sometimes measured by weight and sometimes by volume (via MRI scans or by skull volume). Neur ...
*
Evolutionary biology Evolutionary biology is the subfield of biology that studies the evolutionary processes (natural selection, common descent, speciation) that produced the diversity of life on Earth. It is also defined as the study of the history of life fo ...
*
Human brain The human brain is the central organ of the human nervous system, and with the spinal cord makes up the central nervous system. The brain consists of the cerebrum, the brainstem and the cerebellum. It controls most of the activities of the ...
*
Human evolution Human evolution is the evolutionary process within the history of primates that led to the emergence of ''Homo sapiens'' as a distinct species of the hominid family, which includes the great apes. This process involved the gradual development of ...
*
Neuroscience and intelligence Neuroscience and intelligence refers to the various neurological factors that are partly responsible for the variation of intelligence within species or between different species. A large amount of research in this area has been focused on the neur ...
*
Evolutionary neuroscience Evolutionary neuroscience is the scientific study of the evolution of nervous systems. Evolutionary neuroscientists investigate the evolution and natural history of nervous system structure, functions and emergent properties. The field draws on c ...


References


Bibliography

* * * * * * (Also cited in various publications as volume 16, issue 2, pp. 30–37
For example
* * * * *


External links

* * * * * {{DEFAULTSORT:Brain-To-Body Mass Ratio Animal nervous system Mass Animal intelligence