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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]

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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822 news items

Daily Mail

Daily Mail
Mon, 08 Feb 2016 12:02:33 -0800

With our ability to think our way out of danger and solve problems, humans like to believe it is our big brains that have given us the edge over our animal cousins. However, many creatures have far larger brains than our species in relation to their ...

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 ...
Cops 2.0
Sat, 06 Feb 2016 01:15:44 -0800

Encephalization and allometric trajectories in the genus homo: Evidence from the neandertal and modern lineages. Proc. Natl. Acad. Sci, 100, 15335-15340. Courchesne, E., & Pierce, K. (2005). Brain overgrowth in autism during a critical time in ...

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 ...


Mon, 25 Jan 2016 12:15:27 -0800

Liegt die Intelligenz also vielleicht am „Verhirnungsgrad“ („encephalization-quotient“)? Der gibt die Gehirngröße an, die bei einer bestimmten Körpergröße zu erwarten wäre bzw. die Abweichung davon. Oder liegt sie an der Größe nicht des gesamten ...

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 ...

Air & Space Magazine

Air & Space Magazine
Thu, 07 Jan 2016 10:56:15 -0800

The Troodontids, for example, may have had encephalization quotients (a measure of brain size) higher than dolphins. talos sampsoni.jpg Reconstruction of Talos sampsoni, a newly discovered Troontid Dinosaur. How smart could dinosaurs really get?

Los Angeles Times

Los Angeles Times
Thu, 29 Oct 2015 12:52:30 -0700

Its relative brain size “implies a monkeylike degree of encephalization,” the study authors wrote, similar to gibbons but below that of great apes. Pliobates' wrists also seemed more apelike, in that they allowed for enough rotation to perform careful ...

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