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Researchers have found that frugivores tend to exhibit larger brain size than folivores. One potential explanation for this finding is that frugivory requires ‘extractive foraging,’ or the process of locating and preparing hard-shelled foods, such as nuts, insects, and fruit. Extractive foraging requires higher cognitive processing, which could help explain larger brain size. However, other researchers argue that extractive foraging was not a catalyst in the evolution of primate brain size, demonstrating that some non primates exhibit advanced foraging techniques .Other explanations for the positive correlation between brain size and frugivory highlight how the high-energy, frugivore diet facilitates fetal brain growth and requires spatial mapping to locate the embedded foods.

Expanded Brain Regions and Implications:

The two major perspectives on primate brain evolution are the concerted and mosaic approaches. In the concerted evolution approach, cortical expansions in the brain are considered to be a by-product of a larger brain, rather than adaptive potential. Studies have supported the concerted evolution model by finding cortical expansions between macaques and marmosets are comparable to that of humans and macaques. Researchers attribute this result to the constraints on the evolutionary process of increasing brain size. In the mosaic approach, cortical expansions are attributed to their adaptive advantage for the species. Researchers have attributed hominin evolution to mosaic evolution.

Simian primate brain evolution studies show that specific cortical regions associated with high-level cognition have demonstrated the greatest expansion over primate brain evolution. Sensory and motor regions have showcased limited growth. Three regions associated with complex cognition include the frontal lobe, temporal lobe, and the medial wall of the cortex. Studies demonstrate that the enlargement in these regions is disproportionately centered in the temporal parietal junction (TPJ), lateral prefrontal cortex (LPFC), and anterior cingulate cortex (ACC). The TPJ is located in the parietal lobe and is associated with morality, theory of mind, and spatial awareness. Additionally, the Wernicke’s area is located in the TPJ. Studies have suggested that the region assists in language production, as well as language processing. The LPFC is commonly associated with planning and working memory functions. The Broca’s area, the second major region associated with language processing, is also located in the LPFC. The ACC is associated with detecting errors, monitoring conflict, motor control, and emotion. Specifically, researchers have found that the ACC in humans is disproportionately expanded when compared to the ACC in macaques (a type of Old World monkey).

Studies on cortical expansions in the brain have been used to examine the evolutionary basis of neurological disorders, such as Alzheimer’s disease. For example, some researchers associate the expanded TPJ region with Alzheimer’s disease. However, other researchers found no correlation between expanded cortical regions in the human brain and the development of Alzheimer’s disease.

Cellular, Genetic, and Circuitry Changes:

Human brain evolution involves cellular, genetic, and circuitry changes. On a genetic level, humans have a modified FOXP2 gene, which is associated with speech and language development. The human variant of the gene SRGAP2, SRGAP2C, enables greater dendritic spine density which fosters greater neural connections. On a cellular level, studies demonstrate von Economo neurons (VENs) are more prevalent in humans than other primates. Studies show that VENs are associated with empathy, social awareness and self-control. Studies show that the striatum plays a role in understanding reward and pair-bond formation. On a circuitry level, humans exhibit a more complex mirror neuron system, greater connection between the two major language processing areas (Wernicke’s area and Broca’s area), and a vocal control circuit that connects the motor cortex and brain stem. The mirror neuron system is associated with social cognition, theory of mind, and empathy. Studies have demonstrated the presence of the mirror neuron system in both macaques in humans; However, the mirror neuron system is only activated in macaques when observing transitive movements.