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Encephalization is defined as the amount of brain mass related to an animal's total body mass. Quantifying an animal's encephalization has been argued to be directly related to that animal's level of intelligence. Aristotle wrote in 335 BC: "Of all the animals, man has the brain largest in proportion to his size."[1] Also, in 1871, Charles Darwin wrote in his book The Descent of Man: "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."[2]

In 2004, Dennis Bramble and Daniel Lieberman proposed that early Homo were scavengers that used stone tools to harvest meat off carcasses and to open bones. They proposed that humans specialized in long-distance running to compete with other scavengers in reaching carcasses.[3] It has been suggested that such an adaptation ensured a food supply that made large brains possible.[citation needed]

More encephalized species tend to have longer spinal shock duration.

Encephalization may also refer to the tendency for a species to evolve larger brains through time. Anthropological studies indicate that bipedalism preceded encephalization in the human evolutionary lineage after divergence from the chimpanzee lineage. Compared to the chimpanzee brain, the human brain is larger and certain brain regions have been particularly altered during human evolution.[4] Most brain growth of chimpanzees happens before birth while most human brain growth happens after birth.[5]

Encephalization quotient[edit]

Snell's equation of simple allometry[6] is:


Here "E" is the weight of the brain, "C" is the cephalization factor and "S" is body weight and "r" is the exponential constant. The exponential constant for primates is 0.28[6] and either 0.56 or 0.66 for mammals in general.[7]

The "Encephalization Quotient" (EQ) is the ratio of "C" over the expected value for "C" of an animal of given weight "S".[7]

Species EQ[7] Species EQ[7]
Human 7.44 Dog 1.17
Dolphin 5.31 Cat 1.00
Chimpanzee 2.49 Horse 0.86
Raven[8] 2.49 Sheep 0.81
Rhesus monkey 2.09 Mouse 0.50
Elephant 1.87 Rat 0.40
Whale[clarification needed] 1.76 Rabbit 0.40

This measurement of approximate intelligence is more accurate for mammals than for other phyla of Animalia.

See also[edit]


  1. ^ Russell, Stuart and Norvig, Peter (2003), Artificial Intelligence: A Modern Approach, Upper Saddle River, N.J.: Prentice Hall/Pearson Education, ISBN 0-13-790395-2 
  2. ^ Darwin, Charles, The Descent of Man, and Selection in Relation to Sex (1981 reprint of 1871 ed.), Princeton, New Jersey: Princeton University Press, p. 145, ISBN 0-691-02369-7  See also quote, p.60, in online text of earlier reprint of second (1874) edition.
  3. ^ Bramble DM, Lieberman DE (November 2004), "Endurance running and the evolution of Homo" (PDF), Nature 432 (7015): 345–52, doi:10.1038/nature03052, PMID 15549097. 
  4. ^ See Figures 1 and 2 of Bradbury J (March 2005), "Molecular insights into human brain evolution", PLoS Biol. 3 (3): e50, doi:10.1371/journal.pbio.0030050, PMC 1065704, PMID 15760271. 
  5. ^ Penin, X; Berge, C; Baylac, M (2002). "Ontogenetic study of the skull in modern humans and the common chimpanzees: Neotenic hypothesis reconsidered with a tridimensional Procrustes analysis". American Journal of Physical Anthropology 118 (1): 50–62. doi:10.1002/ajpa.10044. PMID 11953945. 
  6. ^ a b Williams, M.F. (April 2002), "Primate encephalization and intelligence", Medical Hypotheses 58 (4): 284–290, doi:10.1054/mehy.2001.1516, PMID 12027521 
  7. ^ a b c d "Thinking about brain size". Serendip Studeio. Retrieved May 21, 2011. 
  8. ^ Emery, N. J. (2006). "Cognitive ornithology: The evolution of avian intelligence". Philosophical Transactions of the Royal Society B: Biological Sciences 361 (1465): 23–43. doi:10.1098/rstb.2005.1736. PMC 1626540. PMID 16553307. 

Further reading[edit]

External links[edit]

Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/Encephalization — Please support Wikipedia.
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The Daily Galaxy (blog)

The Daily Galaxy (blog)
Wed, 27 Apr 2016 08:56:15 -0700

... see a trend in the encephalization quotient among all organisms as a function of time. The data does not show that. The evidence on Earth points to exactly the opposite conclusion. Earth had independent experiments in evolution thanks to ...
Penn Current
Mon, 11 Apr 2016 08:08:12 -0700

It's also been shown that domesticated animals have smaller brains than their wild counterparts—what's called reduced encephalization—and in some cases experience neoteny, meaning some features don't fully develop. Moore and Morucci sought these ...

Gizmodo Australia (blog)

Gizmodo Australia (blog)
Mon, 11 Apr 2016 18:41:27 -0700

For example, dolphins have a high encephalization quotient, they engage in complex communication, and have big brains. The octopus is capable of associative learning, tameness, and exploratory behaviour. Bees have collective intelligence, a symbolic ...

Discover Magazine (blog)

Discover Magazine (blog)
Sun, 04 Apr 2010 23:17:41 -0700

Maybe at some time point a barrier to increased encephalization (which does look like it is being selected for) was removed: e.g. an adaptation in mothers allowing earlier birth, giving birth to bigger heads (I guess pelvis data should exist), or ...

The Guardian

The Guardian
Wed, 23 Mar 2016 06:02:44 -0700

If the reviews of his latest novel are anything to go by, Julian Barnes's study of Dmitri Shostakovich, The Noise of Time, may just be his masterpiece. And if it is not his masterpiece in the singular sense, then the critical consensus seems to be that ...

New York Times

New York Times
Thu, 28 Jan 2016 04:01:04 -0800

In both parrots and crows, in fact, the ratio of brain to body size is similar to that of the higher primates, an encephalization quotient that yields in both species not only the usual indications of cognitive sophistication like problem-solving and ...


Tue, 08 Mar 2016 15:36:02 -0800

Furthermore, there currently is no reliable measure of intelligence that exists (e.g. encephalization quotient, velocity of cortical neurons, prefrontal cortex, etc.) Read scientific articles (at least 20) about cognitive evolution and then come back ...

Scientific American

Scientific American
Thu, 17 Dec 2015 07:53:10 -0800

One small consolation is an invention of neuroanatomists called the encephalization quotient (EQ). It is the ratio of the mass of the brain of the species under investigation relative to a standard brain belonging to the same taxonomic group. Thus, if ...

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