Talk:Encephalization quotient

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Placed a stub and some basic articles to research. Plenty of room to expand this article with tables and graphs (see refs). :-) Kim Bruning 22:36, 13 Oct 2004 (UTC)

  • As "Encephalisation Quotient" seems to be a far less common term have redirected (UK and US spellings) here. CheekyMonkey 23:01, 13 Oct 2004 (UTC)

Encephalisation Quotient is not the same as brain to body mass ratio, and the current arrangement is not acceptable. The page on Homo floresiensis, for example, now says that H. floresiensis has a similar brain to body mass ratio to H. erectus. This is false: the ratio is dissimilar (and generally considered irrelevant), it is the EQ that is similar, and relevant, and discussed with interest on the talk page.

I think we need a few short articles to define EQ, brain to body mass ratio, brain to spinal cord mass, and any other measures that are used. Then other articles can talk about e.g. the EQs of hominids and the reader will know what the author means. These pages can then reference this one, which should be retitled something like 'relative brain size' (or encephalization, but I think it's worth keeping the existing article with that name). This article can explain current thinking on how to compare brain size between species, and the significance of relative brain size. Securiger's comments below are a good start.

2 other notes:

  • The Gould article linked suggests dividing brain mass by spinal cord mass, not subtracting. Was that what you mean, Ŭalabio?
  • The "Cosmic Evolution" link has a plot of log(brain mass) vs. log(body mass), labelled "A plot of brain mass versus body mass". Since this is confusing, and the relevant parts of the text are rather vague, I favour removing this link, interesting though it is.

Townmouse 13:24, 5 Mar 2005 (UTC)

I agree. Clearly these are different concepts as we have separate tables and values displayed for each. EQ should be broken out into its own page. I separated the terms in the intro to avoid additional confusion. Niluop (talk) 10:56, 31 December 2010 (UTC)

I second the call to remove the incorrect identification between "encephalization quotient" and "brain to body mass ratio". Let's rename this article "encephalization quotient", and create a stub for "brain to body mass ratio" to caution against merging them again. Perhaps a more general article stub could be created to relate them, perhaps "inter-species scaling laws and intelligence". Bayle Shanks 06:25, 10 August 2007 (UTC)

I added the statement about avian and dinosaurian (archosaurian?) encephalization quotient- Paul 1988 that may not be the best (most specific) reference, so if anyone out there knows more about it, by all means, improve it. However I think this interesting fact- that archosaurs have relatively lower motor skill and nervous system demands than mammals and thus smaller brain size despite having similar intelligence- should be in there for those who are using this page as an initial reference. Amdurbin (talk) —Preceding undated comment was added at 00:38, 10 September 2008 (UTC)

Some problems with this article[edit]

This article is way too oversimplified. Some comments:

  • Encephalization Quotient (or Encephalisation Quotient) is not "brain to body mass ratio". It is defined as the ratio between actual brain mass and predicted brain mass—predicted from a certain logarithmic regression curve. If brain mass and body mass of many different vertebrates are plotted on a log-log chart, we find that they mostly lie on two rough lines - an upper line for birds and mammals, and a lower line for reptiles and fish. The slope of this line is approximately 2/3, suggesting that typically M_{brain(est.)} = \alpha M_{body}^{\frac23} where α depends on whether your critter is warm or cold blooded. EQ is the ratio between actual brain mass and the value predicted by this equation. If the exponent was 1, that would be proportional (but not equal) to "brain to body mass ratio", since EQ = M_{brain}/M_{brain(est.)} = M_{brain}/(\alpha M_{body}). But with a 2/3 exponent, it isn't even proportional.
  • Here's a big "bzzzzt" - that 2/3 exponent is fudged. Jerison, the guy who invented EQ, fitted the curve by eye after already deciding by hypothesis that that's what it should be. In fact, the actual slope of his log-log plot is more like 3/4 [1]. So EQ, as originally defined, is horse puckey. Many people still seem to use this fictitious exponent. Well, we'll just fix up the exponent and ignore that.
  • Let r = M_{brain(est.)}/M_{body} Because - approximately speaking - for most species it happens that M_{brain(est.)} = \alpha M_{body}^{\frac34}, it follows that

\begin{matrix}r & = & \alpha M_{body}^{\frac34}/M_{body} \\ \ & = & \alpha M_{body}^{-\frac14} \\ \ & = & \alpha \sqrt[3]\frac{\alpha}{M_{brain}} \\ \Rightarrow M_{brain} & = & \alpha^4/r^3 \end{matrix} Hmm. If we assume that brain to body mass ratio is a measure of intelligence, it turns out that the smarter a creature is, the smaller it's brain is. Clearly, that isn't right. What gives?

In the penultimate line you assume M_{brain} = M_{brain(est)}, i.e. that all animals have an EQ of 1.
You have shown that if brain size is proportional to the 3/4 power of body size, then animals with absolutely smaller brains (smaller animals) have proportionally larger brains. This will be so for any power greater than 0 and less than 1. Townmouse
  • It gets worse. The fit to this line is really pretty rough. We can get lots of completely different slopes by varying our data set a bit. In fact it turns out that the smaller the taxon from which your data comes, the smaller the correlation. That is, the more closely related the species within your sample, the less relevance body mass has to predicting brain size. And within one species, there is practically no relationship.
  • But the really big problem: while it is true that EQ is often used as if it were an estimate for the intelligence of a species, there is no scientific justification for this! Remember, for EQ=1 we have a line running from very small bodied, very small brained creatures at the lower left of the curve, up to very large brained, very large bodied creatures at the top right of the curve. All those species lying on the line have the same EQ. If EQ was a measure of intelligence, we would be claiming that all creatures on this line are of equal intelligence. This is plainly complete nonsense; the line has been statistically constructed so that as many creatures as possible lie as close as possible to it, without any regard to their intelligence (which in most cases has never even been measured).
  • There does seem to be a weak correlation between absolute brain size and intelligence within a species; a rank correlation of about 0.4 has been reported for rat maze solving times and brain mass. That means (more or less) that about 40% of the variation in rat maze solving ability is attributable to brain size—and 60% to "something" else. Between species, there is generally a feeling that there is some sort of relationship, but there are obvious exceptions, and efforts to pin it down to numbers run afoul of the difficulty of numerically comparing intelligence between species.

Securiger 16:55, 8 Nov 2004 (UTC)

Brain-mass minus spinal-cord-mass versus encephalization quotient[edit]

The discovery that the brain-size increases with the surface-area of an animal is great and all, but I remember reading in an Issue of Natural History from the 1980s an article by Stephen Jay Gould where he noted encephalization quotient is good and all, but he observed that animals with small brains for the size of their bodies have brains with about the same size as their spinal cords. He wrote about this in "Bligh's Bounty." He figures that all other things being equal (which they never all), the intelligence of an animal should be proportional to the absolute mass of the brain minus the mass of spinal cord.

-- Ŭalabio 22:27, 2004 Dec 4 (UTC)

I have nothing much to say, other than that I agree with the previous posters that this article needs a major overhauling. The article seems to give a weak description of what EQ is not. It would be nice if we could give a short description of the history of EQ, the problems it was attempting to solve, its current acceptence in evolutionary biology, along with an accurate description of how it is found and what value it has.

I also think it would be appropriate to give a few lines as to why simple brain to body mass ratios fail, along with why brain size is not very valuable for determining intelligence.

Another poster knowing this article is bad, but without the motivation and confidence to fix it himself.



Furthermore, what can we say about people who lost half of their brains, and yet still perform just as well on IQ tests as people who have not lost half of their brains? 22:30, 16 July 2006 (UTC)

What we can say is that it is an urban legend, probably widely distributed by self-improvement promoters, although the origin of the story is uncertain (see, e.g. Snopes). People can receive severe head injuries or strokes and yet still (sometimes, eventually) recover many of their faculties (sometimes at a cost of losing others), but even ~30% loss causes crippling debility (see, e.g. Scans show dramatic brain cell loss in Alzheimer's). -- Securiger 07:29, 20 July 2006 (UTC)
no it isn't. A human being born with only one cerebral hemisphere (and it does have to be a cerebral hemisphere, not anything below the thalamus) can function very highly indeed. Many epileptics have had their corpus callosums cut (split brain patients) and function normally (the hemispheres can communicate somewhat through the anterior and posterior commisures and obviously through other forebrain structures to some degree. It is quite plausible that a man with one hemisphere could function quite well, although he'd be functionally blind on one eye probably and deaf in one ear. He may, or may not have motor issues on one side of the body. I'll leave it to you to chace refs if this really interests you. Duracell (talk) 12:12, 23 July 2011 (UTC)

Article Cleanup Co-Ordination Point[edit]

The cephalization factor[edit]

Found on this phage:

"Starting with the largest brains where we have the most experience, one would assume to a first order that a big brain would imply greater intelligence. But when comparing among species, one must be careful lest one obtain skewed results. For example, very early research in this area compared the ratio of brain weight to body weight as a possible way of deriving relative intelligence among species. But this simplistic approach revealed that both mice and humans have a body weight that is 40 times the brain weight – and small birds have a body weight of only 12 times the brain weight. These results would seem to imply that mice and men are of equal intelligence (many women would agree) and that birds were considerably smarter. But brain weight does not increase linearly with body weight. Instead, the increase in brain size with body size follows a specific exponential rule. In the late Nineteenth Century, Snell derived the following equation relating brain and body weight:

                       E = C S r       

where E and S are body and brain weights, respectively, and C is a constant referred to as a “cephalization factor.” The r is an empirically determined generally accepted exponent that was derived initially by Bonin and is approximately two-thirds for most mammals. The rationale for the two-thirds exponent is based on the premise that the major determinant for required brain size is the body surface. Given a characteristic length of an animal, its surface increases with the square of that length, while its volume increases with the length cubed. If brain size growth were then taken as the animal's surface per volume, then the two-thirds exponent would result. Figure 5.4 shows the brain and body weights for various species with Snell’s equation overlaid representing a best fit of the data. One might note that the polygon connecting the outer limits of the data points shows the elephant and blue whale at the extreme points. Although elephants are generally considered to be fairly intelligent, there is no evidence that they are more intelligent than humans. Therefore, interpretation of this figure requires a methodology for establishing the relative brain capacities of the different species independently of body size. One method commonly used for factoring out body size is to calculate the displacement of each data point from the best-fit line in the polygon and use these residuals to estimate an index of brain size relative to that which would be predicted for a particular animal. Relative brain capacities for different species could then be compared. By entering the brain and body weights for different species into Snell’s equation and solving for C, one can then determine the ratio of the calculated C with that of the average mammalian value. The result is the index referred to as the “encephalization quotient” or EQ. The EQ index enables one to compare the brain capacity of a given species with what would be expected of an animal of comparable weight with average encephalization."

This would mean that each time an animal's mass is doubled, the brain would be for instance 5% smaller to adapt to the new body. This is also seen in other ways. The head of a mouse ir very large compared to its body. Imaging a hore with the same relationship between head and body. A giraffe the size of a rat would have a totally different anatomy, and the different sections of the body would change to adapt. The brain is no exeption, actually this especially goes for the brain. Bt of course, the larger the brain, the bigger the potential, and this in turn can make it grow bigger than one would expect from the rest of the body. Rhynchosaur 23:02, 8 February 2007 (UTC)

When it says "dolphins" have highest EQ, it should state what species. river dolphins have an EQ of only 1.5. Orca between 1.7 and 2...and Orca are considered the most intelligent dolphin of them all. —Preceding unsigned comment added by (talk) 06:55, 10 November 2007 (UTC)

"ocotpuses" is more properly written as "ocotopi"[edit]

I do not know enough about the subject matter to criticize the content, but I did find this spelling/grammatical error distracting. 07:43, 13 June 2007 (UTC)

'octopi' being the correct plural of octopus is an urban myth, it's octopuses

Actually I think it's "octopuses". Bayle Shanks 06:21, 10 August 2007 (UTC)

"Octopodes" is the correct plural. 2:44 29 October 2010 —Preceding unsigned comment added by (talk) 06:44, 29 October 2010 (UTC)

Nope, "octopodes" is the plural of "octopode", not of "octopus". -- Boing! said Zebedee (talk) 06:49, 29 October 2010 (UTC)

Brain size in jumping spiders[edit]

Actually, jumping spiders have (by far) the highest brain/mass ratio of any invertebrates, and in maze-type intelligence tests, can outperform most primates.

Reprint of the 2006 article from New Scientist on jumping spider intelligence:

full article can be read in the cache here:

This is despite their very tiny brain in overall mass!

In fact, I think they have the highest brain/mass ratio of any animal. See the anatomy figure in this article:


Peters' elephantnose fish[edit]

I think that Peters' elephantnose fish should be included in this article. They have a higher brain-to-body mass ratio than humans as well, and are apparently fairly intelligent. Also they can do really neat metal detecting things in total darkness! Here's a blog entry about them: Gary 00:33, 23 August 2007 (UTC)

I do not think so. Even if they have a higher brain-to-body mass ratio, this article is about the encephalization quotient and I found at least one pretty good reference at Google Books that their EQ is not higher than humans: Evolutionary Neuroscience by Jon H. Kaas —Preceding unsigned comment added by (talk) 01:11, 9 January 2011 (UTC)
If someone can find it's actual brain- and body weight, it's just putting the numbers into the formula (a simple calculation, no original research there) and see what we get.
Edit: From the Brain-to-body mass ratio discussion: : According to Göran E. Nilsson's paper Brain And Body Oxygen Requirements Of Gnathonemus Petersii, A Fish With An Exceptionally Large Brain (1996) its brain-to-body mass ratio is 0.0309±0.0034 ≈ 1/34 —Preceding unsigned comment added by (talk) 01:30, 9 January 2011 (UTC) Petter Bøckman (talk) 12:31, 9 January 2011 (UTC)
I partially agree with Gary. Although the elephantfish is not directly comparable to mammals, it is comparable to manta rays, which are given in the Wikipedia article (under the subtopic "Comparisons with non-mammalian animals") as being the fish with the highest EQ. Some elephantfish have a brain/body mass ratio 100 times higher than manta rays. Small elephantfish such as the 5.85g Gnathonemus Petersii mentioned above with its 0.177g brain is too small to compare reliably with larger fish, though it does hint of higher intelligence. There are species of elephantfish up 1.5 meters long and they also have exceptionally large brains. They would provide meaningful comparison if anybody can find the data.
On the topic of actually calculating the EQ from the data given in the article, I'm rather inept mathematically, so it may just be me, but I've been unable to work out how to calculate EQ from the data for the small elephantfish given above by plugging in the values 5.85g body and 0.177g brain. Can anybody else make the formula work?
Miriam e (talk) 00:00, 22 May 2014 (UTC)

Problem with units of the factor 0.12[edit]

There is a problem with the physical units of the coefficient 0.12 in the formula of the article. This number only works if brain mass is in grams while body mass is in kilograms. Not very beautyful. The true value of this coefficient, with proper units, is

 0.12\ \frac{\mbox{kg}}{\mbox{g}^{2/3}} = 120\ \frac{\mbox{g}}{\mbox{g}^{2/3}} = 120\ \mbox{g}^{1/3} = 120 \cdot (0.001\ \mbox{kg})^{1/3} = 12\ \mbox{kg}^{1/3}

I will correct the article accordingly. 13:46, 29 August 2007 (UTC)

Sorry, I was wrong. I think the constant was correct before

 0.12\ \mbox{g}^{1/3} = 0.012\ \mbox{kg}^{1/3}

Sorry for the confusion. 14:49, 29 August 2007 (UTC)

Brain/body masses don't have to be grams, or any particular unit, the equation is unit-balanced, as long as you keep your units consistant, the equation doesn't care if they are grams, ounces, tons, or double-decker buses. I've deleted the reference to grams. -- PaulxSA (talk) 11:11, 12 January 2008 (UTC)

The main problem seems to be that the matter is far from forgone conclusion[edit]

The various "citation needed" are irrelevant - I have found plenty. However, the criticism offered here by [2] and others is viable. The problem is not lack of sources, but lack of research.

I think the best course of action is to state clearly that the issue is heavily criticized and to remove the numerous "citation needed" marks.

Zarnivop (talk) 10:26, 15 September 2008 (UTC)

Roughly speaking[edit]

"Roughly speaking, the larger an organism is, the more brain weight is required for basic survival tasks, such as breathing, thermoregulation, senses, motor skill, etc"

How roughly? Whom are speaking? Can anyone find any explanation why more brain weight is required for breathing of larger animal? Same goes for motor skills. If something, larger animal breathes, thermoregulates, walks, and so on at lower rate (in actions per second), thus requiring less computation for doing this. That is just basic logic. If that logic is invalid and more brain weight is indeed 'required', that would be rather extraordinary and outstanding - and would require some research which explains why more brain mass is required for doing less computationally intensive task. —Preceding unsigned comment added by (talk) 13:05, 8 August 2009 (UTC)

I don't think this is entirely true. For mammals, the general rule of thumb is the larger the body, the larger the brain, but the larger the body the smaller the relative size. To the degree that we can draw any conclusion from this, then it appears that "basic survival tasks" (breating, heartbeat, thermoregulation) is rather idependent of body size in mammals. Petter Bøckman (talk) 08:49, 3 December 2010 (UTC)


Well, I'd also like to know why exactly larger animals need larger brains for everything and why it should always be the same factor. For example for touch I'd expect a quadratic increase of first layer neurons when trying to keep the skin sensor density equal. Many of the later processing steps would probably depend less on size. For hearing on the other side, where's the point in spending a single neuron more on that, except perhaps for some low-frequency sounds that are physically not recognizable in smaller animals? On the motor side of things, doesn't it depend mainly on the number of muscles, not on the number of muscle fibers how many neurons you need? Exactly 106,554,278,101

Intelligence Citations Bibliography for Articles Related to Human Intelligence[edit]

I have posted a bibliography of Intelligence Citations for the use of all Wikipedians who have occasion to edit articles on human intelligence and related issues. I happen to have circulating access to a huge academic research library at a university with an active research program in those issues (and to another library that is one of the ten largest public library systems in the United States) and have been researching these issues since 1989. You are welcome to use these citations for your own research and to suggest new sources to me by comments on that page. -- WeijiBaikeBianji (talk) 23:05, 2 July 2010 (UTC)


The section on Criticism argues without having a good argument. It is only fluff at this point. It should be removed or completely re-written.

Recent research indicates that whole brain size is a better measure of cognitive abilities than EQ for primates at least.[13]

"While Stegosaurus was undoubtedly a simple and unintelligent animal, this fact undermines the idea on which EQ is based - that a larger animal requires a larger brain to look after its basic functions." This is not clear at all.

"If Stegosaurus could survive with this tiny brain, this can only mean that any animal with anything bigger must be using it for non-essential abilities." This is not necessarily true; humans evolved bigger brains so they could manipulate their environment; why couldn't stegosaurs have done the same with bigger brains? Answering, "No, because they were stegosaurs" would be a circular argument.

"Some of these abilities may be sensory and/or physical, and some may be intellectual. The actual intelligence of an animal therefore depends on the size of the brain and the proportion of the brain that is used for intellectual abilities, rather than advanced sensory or physical skills." This is similar to Larmarkianism. The quote basically says the animals get intelligent is by using their intelligence.

"Critics[who?] point out that EQ gives only a very rough estimate of these proportions." This sentence should either be supported or removed. (talk) 18:02, 14 December 2010 (UTC)

I agree with the above (unsigned) criticisms. I would go farther and say that many sentences in the article "should either be supported or removed." The article appears to be no more than a rough draft, which may be used as a skeleton for other editors to build a real article out of, so it may warrant an "under construction" header before it's unsupported claims start getting cited by students unaware of how Wikipedia works. I don't want to put the header at the top since I lack the knowledge to build it.HkFnsNGA (talk) 19:46, 24 December 2010 (UTC)

It's a bad argument because stegosaurs didn't keep all the neurons for running bodily functions in their brains. Whether you choose to call it a second brain or a thickening of the spinal cord, there's a cavity between their hips that was probably filled with neurons for controlling bodily functions, which you would have to include in any measure of the minimum amount of brain matter it takes to control an animal of that size. In any case, the argument is unsupported (the article linked to doesn't say anything about the brain size of stegosaurus or even about its EQ). I'm removing it. (talk) 02:03, 19 February 2013 (UTC)

Source? Last time I saw anything on it, the swelling was considered a fat store, no an "extra brain". Petter Bøckman (talk) 06:45, 19 February 2013 (UTC)

ratio of allo/isoctx to other neural tissue[edit]

I think this measure is a good start. But for mammals, I'm not certain why we are not taking into account the ratio of cortical to non-cortical tissue as part of this measure. Certainly if you want primates to come out on top that would do it. and humans most of all of course. Studies of brain evolution (look e.g. at David Van Essens work) often look at the expansion of cortical areas from e.g. macaque (presumed similar to an ancient ancestor of hours) or baboon to human. If most of your brain mass is non-cortical forebrain and below, then you are rat-like. A rat has a tiny cortex relative to the mass of its subcortical structures. A human (or dolphin) has a vast cortex relative to mass of sub cortical strcuts Duracell (talk) 12:12, 23 July 2011 (UTC)

Th KR link, in the chart, second from the bottom, leads to a disambiguation page. Sdmitch16 (talk) 05:08, 20 August 2011 (UTC)


Could someone clarify "Whale". Also "KR", From the table at the top of the article. Zeimusu | Talk page 20:09, 21 August 2011 (UTC)

In view of the history, the "KR" entry was clearly vandal nonsense – a veiled racist reference to Koreans. I took it out; unexplained abbreviations are useless anyway. --Florian Blaschke (talk) 20:07, 22 September 2011 (UTC)

Bad Source?[edit]

(Cut 'n' Pasted from the Brain-to-body mass ration article)

The source from the table links to [1] This is turn mentions another source: Kuhlenbeck, 735.

I have been looking for "Kulhenbeck, 735" on Google and all I get are different websites listing the same table. A quick look on Google Scholar using various search terms ("Kulhenbeck body-to-brain ratio" etc.) is of little help. The only data I've been able to find was on another page from serendip:

Even they suggest Kuhlenbeck may be wrong, even though everyone sources his data from their website. Long story short - this sounds like a mistake that has been repeated so often people think it's the truth. Should we remove it?

--Lyrical Jesse James (talk) 09:43, 10 September 2011 (UTC)

Human EQ[edit]

Homo sapiens quotient is claimed to be 7.4-7.8 whereas on brain size it is listed as 4.6. I cannot access the Aiello and Wheeler paper cited there to verify the number. There is no reference on this page for EQ = 7.4-7.8. Can someone with journal access please resolve this. I have placed a similar request on brain size. FloreatAntiquaDomus 10:32, 13 April 2012 (UTC)

In addition, this Talk Page is damn hard to navigate. — Preceding unsigned comment added by FloreatAntiquaDomus (talkcontribs) 10:32, 13 April 2012 (UTC)

Comparisons with non-mammalian animals[edit]

Dolphins are included in this section in the article, which is confusing in this context because they are mammals. The note about dolphins should be moved to a different section of the article. -- NoahSpurrier (talk) 07:37, 8 May 2012 (UTC)

White-fronted capuchin[edit]

The White-fronted capuchin apparently has an anomalously high encephalization quotient[3]... AnonMoos (talk) 15:20, 1 December 2012 (UTC)

Criticism section[edit]

The criticism section needs some revision. There appears to be a word/words missing ("complexity of..."). It would also benefit from a more comprehensive consideration of alternative measures, such as size of relevant brain part(s) over brainstem volume; number and density of neurons; a more thorough explanation of gyrification, etc. There is a lot more research available that is critical of EQ as a means to eliminate allometry and measure residual encephalization, and it is poorly represented here. — Preceding unsigned comment added by (talk) 19:43, 7 April 2013 (UTC)

Feel free to ad it! I'll help with formating and things like that if necessary. Petter Bøckman (talk) 20:40, 7 April 2013 (UTC)

Edited Reference (currently No. 15)[edit]

I've added missing author- and title-data to the reference No. 15:

  • Susanne Shultz and R.I.M Dunbar. Both social and ecological factors predict ungulate brain size.

But doing so I'm unsure, if this reference really is fitting to it's citing text-passage ...
Is there some more knowing expert on hand to verify this?
Jaybear (talk) 13:55, 4 October 2013 (UTC)

EQ for humans, what value is true?[edit]

Brain size says: "The encephalization quotient for humans is approximately 4.6". I quickly checked the ref and it seems to not to be about 7. (4.75 from the graph..). comp.arch (talk) 13:39, 14 January 2014 (UTC)