Brain Evolution

There is something unusual about the human brain and its behavioral capacity

The neocortex is disproportionately large in

humans

Neuroscientists have paid rather little attention to the study of brain evolution

Neuroscientists

Clade

Theories are highly speculativeThere is a single goal or direction to evolution

Brain Evolution

Neuroscience

Misconceptions about Brain Evolution

Interestingly, domestic

animals with our efforts

to improve a wild stock, generally

have reduced

brain size.

Butthead

Tarsiers

Neocortex Origins

Not that new at all. Similar to the Dorsal Cortex in

birds and reptiles

V.

Dorsal Cortex Neocortex

Ancient Neocortex were likely to not have the differentiated layers and

neuron types

Evolution of Primates:The early years

Evolution of Primates:Improvements

Old and New world monkeys developed their trichromatic vision separately.

Tarsiers and Owl monkeys are secondarily nocturnal

Hominines and Chimpanzees

Early Primates

Early primates were lemur-like in body form, and their brains were shaped like those of present-day lemurs, although smaller.

V3 DM MT

V1

Visual SystemSomatosensory Cortex

VP

S1 S2

Ancestral StateDerived State

Most of the large number of specializations that likely evolved in early primates or their

immediate ancestors

Evolution of Hominin Brains

Human brains are not symmetrical in shape, so that the planum temporale, the sheet of

cortex on the lower surface of the lateral sulci, is usually larger in the left cereberal

hemisphere than on the right.

Interestingly, however, great apes exhibit the same asymmetry of the temporal lobe as humans, despite their lack of language.

Australopithecus~600 cc

Homo habilis                    ~800 cc

Homo erectus~1000 cc

Homo sapiens~1400 cc

The issues of a Big Brain

Inverse Ninja Law: The more ninjas there are, the weaker each

individual ninja is

Selection has to be based on a few developmental

mechanisms

Higher metabolic cost

may require better diet.

Large brains generally devote much more of their mass to connections. Small morphological adjustments

dramatically change the area affected.

Primates brains simply have many more neurons than rodent brains of the same size