Changes in Relative Size of Cerebral Cortex

Changes in Cerebral Cortex

Cerebrum has progressively increased in size, especially cerebral cortex: vision, memory, reasoning, manipulative ability. Necessary to cope with environmental change.

Why do Primates have Large Brains for their Body Size?

Consequence of arboreal environment, natural selection favoured more accurate visual, tactile perception and coordination between stimuli and muscular response.

Unlike smell or hearing, reliance on vision to move, locate and manipulate food, generates loads of complex sensory info to be processed and stored.

In primates, executed by cerebral cortex.

What is an Arboreal Environment?

Tree-like Environment

Brain Size Difference

Associated with mostly cerebrum/cerebral cortex. Human’s range 900-2200cm3, average 1350cm3 in adulthood, other apes range 400cm-500cm3.

Frontal lobe has greatest enlargement, in humans 47% of total cortical surface, apes = 33%.

50% surface area increase of human brain, than brain with no convolutions

Tool Making

Seen in humans and chimpanzees, opposed to tool use, requires predetermined image of completed tool, requiring highly developed brain

Behavioural Responses

Greater variety to meet environmental challenges e.g. interactions with relatives, allies and adversaries. Mutual cleaning reinforces relationships. Threats and fighting maintain dominance hierarchy.

Behavioural flexibility places further physical specialisation

Cranial Capacity

Brains of early hominins not fossilised but brain size is determined by measuring volume inside cranium using an endocast.