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Evolution of the brain and intelligence.

Gerhard Roth¹, Ursula Dicke

¹Hanse Institute for Advanced Study, D-27753 Delmenhorst, Germany. gerhard.roth@uni-bremen.de

Trends in Cognitive Sciences

|May 4, 2005

Summary

Human intelligence, while exceptional, evolved from enhanced primate traits like language and imitation, not unique properties. Key factors include cortical neuron count and processing speed, surpassing many mammals.

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Area of Science:

Comparative cognition
Neuroscience
Evolutionary biology

Background:

Intelligence has evolved independently across vertebrate species.
Assumptions about intelligence often link it to brain size and encephalization.
Previous studies suggest primates, elephants, and cetaceans exhibit higher intelligence than 'lower' mammals.

Purpose of the Study:

To investigate the key neurobiological factors underlying intelligence across different species.
To compare the information-processing capacity of human brains with other mammals.
To determine if human intelligence relies on unique properties or enhanced existing traits.

Main Methods:

Analysis of brain properties, including absolute and relative brain size, cortex size, prefrontal cortex size, and encephalization.
Evaluation of the number of cortical neurons and conduction velocity as indicators of information-processing capacity.
Comparative analysis of cognitive traits such as theory of mind, imitation, and language in humans and non-human primates.

Main Results:

The number of cortical neurons and conduction velocity correlate more strongly with intelligence than brain size metrics.
Humans possess a high number of cortical neurons, comparable to whales and elephants.
Human intelligence appears to stem from an enhancement of cognitive abilities observed in non-human primates.

Conclusions:

Cortical neuron count and conduction velocity are critical for high-level information processing and intelligence.
Human intelligence is characterized by an amplification of primate-like cognitive functions, including theory of mind, imitation, and language.
The evolution of intelligence is a complex process involving both independent evolution and the enhancement of shared traits.

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