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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)

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Contents 1 Some problems with this article 2 Brain-mass minus spinal-cord-mass versus encephalization quotient 2.1 ============ 2.2 Article Cleanup Co-Ordination Point 2.2.1 Discussion

[edit] Some problems with this article

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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 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 / (αM_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 , it follows that
  

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)

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

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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." http://web.archive.org/web/20010709234346/http://yoyo.cc.monash.edu.au/~tzvi/GOULD.html 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)

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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.

-b

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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? 24.16.15.81 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)

[edit] Article Cleanup Co-Ordination Point