Scientific American Sep 2018

(Jeff_L) #1
September 2018 ScientificAmerican.com 63

Cat "¹ ́‘žŠ ́ ́ym
ȟ ̈¹ïĀ›D ̈y

Human $D`DÕùy  ̈yțD ́ï

Cerebral
cortex

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Cerebellum

yàyUy ̈ ̈ù®

CerCerebeebellallarr
neuron count
unknown

CerCerebeebellallarr
neuron count
unknown

 ̈yțD ́ï "¹ ́‘žŠ ́ ́ymȟ ̈¹ïĀ›D ̈y Human ›Ÿ®ÈD ́Ćyy $D`DÕùy Cat

Circle area shows
number of neurons

ÀUŸ ̈ ̈Ÿ¹ ́

ÀĈUŸ ̈ ̈Ÿ¹ ́

‹ĈUŸ ̈ ̈Ÿ¹ ́

0 12345601234567891011

Chimpanzee Human

Dà ̈ß ́†D ́`Ă "DïyŸ ́†D ́`Ă ùÿy ́Ÿ ̈y

02341

0

10

20

30

40

50

60

70

80

90

100

Macaque

‘yÊĂyDàåË

0yà`y ́﹆mù ̈ï
àDŸ ́<¹ ̈ù®y

0ùUyàïĂ

D`›m¹ïàyÈàyåy ́ïå 5ày ́m ̈Ÿ ́y
¹ ́yåùU¦y`ïŸ ́DåïùmĂ

September 2018 ScientificAmerican.com 63

BRAIN VS.
BODY SIZE
Humans have a large brain
compared with its expected
dimensions for their body mass.
The encephalization quotient (EQ) as
it is known is 1 if the brain/body mass
ratio meets expectations. Humans have
D ́1¹†é~è1冹à ̈¹ ́‘žŠ ́ ́ymȟ ̈¹ï
whales are 2–3; elephants are 1–2;
macaques are 2; and
cats are 1.

NEURON
NUMBER
A much scrutinized measure
of brainpower has to do with the
number of an animal’s neurons—and
where they are located. Humans have
more neurons in the cerebral cor tex
16 billion than almost all other
mammals although the long-
Š ́ ́ymȟ ̈¹ïĀ›D ̈y
has more.


PAC K I NG
IN THE BRAIN
CELLS
In humans the cerebral cortex
makes up 82 percent of the brain’s
mass but contains only 19 percent
of the total neurons whereas the
cerebellum holds 80 percent
or so of the neurons but only
occupies 10 percent
of its mass.
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