<b><i>Background/Aims:</i></b> A recent duplication of the gene encoding SLIT-ROBO Rho GTPase-activating protein 2 <i>(SRGAP2)</i> in the primate lineage has been proposed to be associated with the human-specific extraordinary development of intelligence. There is no report regarding the role of the <i>SRGAP2</i> gene in the expression of neural traits indicating intelligence in mammals. <b><i>Methods:</i></b> A phylogenetic tree of the <i>SRGAP2 </i>gene from 11 mammals was reconstructed using MrBayes. The evolution of neural traits along the branches of the phylogenetic tree was modeled in the BayesTraits, and the dN/dS ratio (i.e. the ratio between the number of nonsynonymous substitutions per nonsynonymous site and the number of synonymous substitutions per synonymous site) was estimated using the codon-based maximum likelihood method (CODEML) in PAML (phylogenetic analysis by maximum likelihood). <b><i>Results:</i></b> Two neural traits, namely brain mass and the number of cortical neurons, showed statistical dependency on the underlying evolutionary history of the <i>SRGAP2</i> gene in mammals. A significant positive correlation between the increase in cortical neurons and the rate of nucleotide substitutions in the <i>SRGAP2</i> gene was observed concomitantly with a significant negative correlation between the increase in cortical neurons and the rate of nonsynonymous substitutions in the gene. The <i>SRGAP2 </i>gene appears to be under intense pressure of purifying selection in all mammalian lineages under stringent functional constraint. <b><i>Conclusion:</i></b> This work indicates a key role of the <i>SRGAP2</i> gene in the rapid expansion of neurons in the brain cortex, thereby facilitating the evolution of remarkable intelligence in mammals
