Brain reorganization, not relative brain size, primarily characterizes anthropoid brain evolution.

Area of Science:

• Evolutionary biology
• Neuroscience
• Comparative anatomy

Background:

• Primate brain evolution is characterized by changes in size and internal organization.
• Understanding the drivers of structural neural diversity across primate species remains a challenge.
• Key questions involve the relative contributions of mosaic reorganization versus overall brain size, specific mosaic changes, and their evolutionary timing and processes.

Purpose of the Study:

• To quantify the contribution of mosaic brain reorganization versus relative brain size to primate neural diversity.
• To identify which specific mosaic changes are most influential in explaining this diversity.
• To determine the evolutionary origins, rates, and processes of mosaic reorganization shifts across primate lineages.

Main Methods:

• Employed novel comparative methods to analyze temporal origins, rates, and processes of evolutionary changes on individual primate lineages.
• Utilized newly available volumetric data for key brain structures (prefrontal cortex, frontal motor areas, cerebrocerebellum) from 17 primate species, including humans.
• Integrated findings with existing electrophysiological, tract-tracing, and functional connectivity MRI data.

Main Results:

• Mosaic changes in brain evolution significantly contribute more to explaining neural diversity than relative brain size changes over 40 million years of anthropoid evolution.
• Identified distinct mosaic patterns that are differentially selected during periods of brain size increase or decrease.
• Revealed lineage-specific evolutionary specializations and deep evolutionary roots for mosaic patterns related to motor control and learning.

Conclusions:

• Mosaic brain reorganization is a more significant driver of primate neural diversity than overall brain size.
• Specific patterns of mosaic reorganization, particularly those linked to motor control and learning, show deep evolutionary origins and are subject to lineage-specific selection.
• Evolutionary shifts in mosaic reorganization are complex, with distinct temporal origins and processes across primate lineages.