The evolutionary origin of the mammalian cerebral cortex

Area of Science:

• Neuroscience
• Evolutionary Biology
• Comparative Anatomy

Background:

• The mammalian neocortex is often viewed as a key evolutionary advancement for cognitive abilities.
• Alternative hypotheses suggest its origin may be linked to contingent, non-cognitive selective pressures.

Purpose of the Study:

• To propose an alternative evolutionary origin for the mammalian neocortex.
• To investigate the role of nocturnal adaptation and olfactory system development in neocortex evolution.
• To compare neocortex evolution with brain structures in reptiles and birds.

Main Methods:

• Comparative analysis of brain structures in mammals, reptiles, and birds.
• Hypothesizing functional shifts based on anatomical changes.
• Examining the relationship between optic tectum reduction and cerebral cortex expansion.

Main Results:

• Nocturnal adaptation in early mammals led to optic tectum (superior colliculus) reduction.
• Olfactory system development coincided with cerebral cortex expansion.
• The cerebral cortex, a laminar structure, likely replaced the optic tectum in integrative functions.
• The optic tectum did not redevelop in diurnal niches, making the cerebral cortex the primary system.
• Reptiles and birds show increased optic tectum size and complexity, with nonlaminar forebrain growth.

Conclusions:

• The mammalian neocortex originated from adaptations to nocturnality and olfactory-driven behaviors, not directly from selection for higher cognitive capacities.
• The reduction of the optic tectum and expansion of the cerebral cortex represent an irreversible evolutionary event.
• Comparative neuroanatomy highlights different evolutionary trajectories in brain structure among vertebrates.