Largest Brain on planet, 30 lbs!

Belongs to Sperm Whale

Absolute Brain Weight – Does it reflect intelligence?

Species Adult Brain Weight (grams)

Chimpanzee 450

Human 1,350

Bottlenosed dolphin

1,600

African elephant

6,075

Fin whale 7,200

Sperm Whale

9,200

Relative Brain WeightOf all animals, man has the largest brain

in proportion to his size” - Aristotle

Species Brain to Body Weight

Human 2.1 %

Bottlenosed dolphin 1.2 %

Chimpanzee 0.70 %

African elephant 0.50 %

Killer whale 0.10 %

Cow 0.08 %

Sperm Whale 0.02 %

Encephalization: Increase in brain size during evolution of SPECIES, with no concomitant increase in body size

Encephalization Quotient (EQ)

???????? 9.0

Human 7.4

Dolphin 5.6

Killer whale 2.9

Chimpanzee 2.5

Rhesus Monkey 2.1

Elephant 1.9

Whale 1.8

Dog 1.2

Cat 1.0

Horse 0.9

Sheep 0.8

Mouse 0.5

Rabbit 0.4

Anatomical estimate of species’ intelligence based on brain/body size and not behavior

EQ = ratio of brain weight of animal to brain weight of “typical” animal of same body weight

EQ represents residual value of brain mass

Encephalization Quotient (EQ)           1 g brain for hummingbird

Hummingbird 9.0

Human 7.4

Dolphin 5.6

Killer whale 2.9

Chimpanzee 2.5

Rhesus Monkey 2.1

Elephant 1.9

Whale 1.8

Dog 1.2

Cat 1.0

Horse 0.9

Sheep 0.8

Mouse 0.5

Rabbit 0.4

EQ through evolutionary time

• Are we evolving into smarter and smarter creatures? Or was humanity a fluke?

• In other words, was there a neural arms race in the past or an unusual mutation process in one line of primates?

Evolution of behavioral complexity

Neural arms race in mammalian group only

Four leaps in braininess

1. To Primate

2. To Australopithecus

3. To Hominid

4. To Homo sapiens

Brainy Newcomers

Convolution Index = wrinkliness

• BUT: Cortex width: human 2.9 mm, dolphin 1.7 mm and conversative (not progressive) organization

Not a straight ascent to modern humans

• Coincided with unstable weather (4 ice ages)

...And Then There Was One • Sixteen Species of

Extinct Humans • Ardipithecus ramidus

Australopithecus anamensisAustralopithecus afarensisAustralopithecus bahrelghazaliAustralopithecus aethiopicusParanthropus boiseiParanthropus robustusAustralopithecus africanusAustralopithecus garhiHomo rudolfensisHomo habilisHomo ergasterHomo erectusHomo antecessorHomo heidelbegensisHomo neanderthalensis

• Homo sapiens

Sensory information is processed subcortically, and then first is processed cortically in primary modality areas

Primary versus Association Cortex

BUT the dolphin brain is organized differently

General Features of Encephalization

• Increase in absolute & especially relative brain size– Cortex enlarged compared to lower

structures• More brain tissue for sensory functions

compared to motor functions • Increase in Associative areas• Rise of importance of biophysical senses

compared to chemical senses

Mammals: Smell, Sight, or Sound Brains

Number of olfactory receptor cells– Human 40 Million– Rabbit 100 M– Dog 1000 M

% volume Rat Human

Cortex 31 77

Midbrain 13 8

Brainstem 7 2

Cerebellum 10 10

Spinal cord 35 2

Can human brain get any bigger?Perhaps, but need to consider speciation,

torque, and pelvic evolution.

Hominid Million yrs Weight (g)

Australopithecus 5.0 500

H habilis 2.5 725

H erectus 1.7 1000

H heidelbergensis 0.6 1200

H neanderthalensis 0.2 1500

H sapiens 0.2 1350