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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 B.C. "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]


In Snell's equation of simple allometry[6] "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.

Evolution of the EQ[edit]

The evolution of the EQ shows a close correlation with the evolution of the diversity of life generally. During the Paleozoic the EQ generally increased throughout the period, peaking in the late Carboniferous and early Permian. However, the Permian - Triassic mega-extinction events 251 million years ago reversed this trend. Occurring through the probable release of oceanic methane clathrates, and the burning of coal from the Siberian volcanic basalt traps, it saw the elimination of 96% of species, and slowed the rate of EQ development, such that only by the end of the Cretaceous Period had the EQ recovered to its earlier level, with the appearance of the dromaeosaurids and troodontids. A second K-Pg (Cretaceous-Paleogene) extinction event of 66 million years ago, with the extinction of the non avian dinosaurs, ammonites and many other creatures this time saw 78% of species become extinct. These events had a huge effect in setting back the further evolution of the EQ. In the case of humans, the rise in encephalisation from Australopithecus to Homo neanderthalensis, with a brain capacity of 480cc to 1450cc, over 1.5 million years, is an equivalent to an increase of 125,000 additional brain cells per generation. Such an increase without a great increase in technology suggests that it was fueled by a social and not a technological imperative.[citation needed]

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. doi:10.1098/rstb.2005.1736. 

Further reading[edit]

External links[edit]

Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/Encephalization — Please support Wikipedia.
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839 news items

Mother Nature Network (blog)

Mother Nature Network (blog)
Tue, 06 Oct 2015 08:34:26 -0700

Instead of just comparing brains to bodies, scientists can also use the encephalization quotient (EQ) to compare an animal's brain mass with the typical brain mass of related species. Humans' EQ of 6.56 is the highest known, followed by several ...
The Verge
Sun, 20 Sep 2015 06:00:30 -0700

We can make rough guesses using figures like brain mass and encephalization quotient, and we can note peculiar or impressive bits of behavior, but that's about it; we know we're number one, and that's the only thing we know for sure. But I'll say this ...
Discover Magazine (blog)
Sun, 04 Apr 2010 23:17:41 -0700

I personally don't find an increased rate of encephalization 200-300 years ago that implausible; the emergence of behavioral modernity about 50 thousand years ago resulted in much more rapid cultural evolution than before. But perhaps John Hawks could ...
Thu, 12 Feb 2015 06:55:12 -0800

Perhaps more important is the encephalization quotient (EQ), a formula to measure brain intelligence in animals created in the 1970s by Harry Jerison, professor of neurostudies at the University of California, Los Angeles. Jerison found that ...


Tue, 18 Aug 2015 05:39:32 -0700

... Weight Loss, Fitness, and Aging,” writes in an email interview. De Vany disagrees with the suggested role of starch and carbohydrates in the study, saying that nutrition from seafood and other prey was the key to rapid brain development, or ...


Tue, 14 Apr 2015 12:17:35 -0700

One way to compare brains is the encephalization quotient (EQ), the ratio between actual brain size and that expected from the species' body size. An EQ above 1.0 indicates a brain larger than expected for the size of the animal. Humans are at the top ...
Thu, 23 Apr 2015 20:11:15 -0700

A commonly used term to describe nutritional needs and energy expenditure in humans – basal metabolic rate – could also be used to give insight into brain size of ocean fish, according to new research by Dr Teresa Iglesias and Dr Dan Warren at ...


Wed, 13 May 2015 09:22:35 -0700

Encephalization quotient is one way to measure how big an animal's brain is compared with its expected size based on the species' body mass. Values larger than one mean a larger-than-expected brain, while values smaller than one mean a species is ...

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