The art of thinking · 7 · Brain and learning
Encephalization
Also known as: Encephalization quotient, EQ (brain size)
German: Enzephalisation
In comparative neuroscience and evolutionary biology, encephalization is the increase of brain size relative to body size in the course of evolution; Harry J. Jerison’s encephalization quotient (1973) compares a species’ brain size with the size expected for an animal of its body mass.
- Cognitive psychology
- Brain research
In one sentence
Encephalization: the evolutionary increase of brain size relative to body size, measured between species with Jerison’s encephalization quotient (1973).
Example
Because larger animals have larger brains, an elephant’s brain is heavier than a human’s. The encephalization quotient corrects for body size, which is why it is used to compare species — never individual people.
What the research shows
Harry J. Jerison introduced the encephalization quotient (EQ) in Evolution of the Brain and Intelligence (1973): the ratio of a species’ actual brain size to the brain size expected for a typical mammal of the same body mass. Primates, and among them humans, have high quotients. Gerhard Roth and Ursula Dicke (2005) compared measures across mammals and argued that the EQ alone predicts differences in intelligence between species poorly; the number of cortical neurons and the speed of information processing fit better.
Evidence status
The EQ is an established measure in comparative biology and is debated as a proxy for cognitive ability between species. It is a comparison between species. It does not support any statement about individual people, and nothing in this research shows that a person with a larger brain thinks faster or better.
How it applies
- Careful wording: Texts that mention brain size should say that comparisons are made between species, and should never imply a ranking of people.
- As background: Every person has a human brain; encephalization explains how that brain came about in evolution, not how one person’s thinking differs from another’s.
External references
- Jerison, H. J. (1973). Evolution of the Brain and Intelligence. New York: Academic Press.
- Roth, G., & Dicke, U. (2005). Evolution of the brain and intelligence. Trends in Cognitive Sciences, 9(5), 250–257. https://doi.org/10.1016/j.tics.2005.03.005
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