Adult Neurogenesis: An Evolutionary Perspective.

Area of Science:

• Neuroscience
• Evolutionary Biology
• Comparative Anatomy

Background:

• Adult neurogenesis, the generation of new neurons in the adult brain, was historically viewed as an evolutionary regression (atavism).
• A prevailing notion suggests a "phylogenetic reduction" of lifelong neurogenesis in favor of brain stability for complex cognitive functions.
• Neurogenesis varies significantly across the animal kingdom, with mammals possessing fewer neurogenic zones compared to species like fish.

Purpose of the Study:

• To re-evaluate the evolutionary trajectory of adult neurogenesis in mammals, particularly in the context of brain complexity.
• To investigate the functional significance of adult neurogenesis in mammalian brains, specifically the dentate gyrus.
• To challenge the "phylogenetic reduction" hypothesis by examining neurogenesis in the human hippocampus.

Main Methods:

• Comparative analysis of neurogenesis across different animal taxa.
• Review of existing literature on adult neurogenesis in mammalian brains.
• Focus on the dentate gyrus and hippocampal neurogenesis in humans.

Main Results:

• Adult neurogenesis is present throughout the animal kingdom, albeit with considerable variation.
• Mammals may have reduced the number of neurogenic zones but retain highly functional new neurons within these zones.
• Humans exhibit substantial levels of adult neurogenesis in the hippocampus.

Conclusions:

• The discovery of adult neurogenesis does not represent an evolutionary loss but rather a shift in its distribution and function.
• The significant neurogenesis in the mammalian dentate gyrus suggests an evolutionary adaptation favoring plasticity.
• Evidence supports an evolutionary trend toward enhanced neurogenesis-based plasticity, particularly in humans.