HUMAN BRAIN SIZE: A MIRACLE IN THE GENES
The biologist J. B. S. Haldane has noted that the extraordinary increase in the human brain size was the fastest evolutionary transformation known.
To investigate whether this rapid expansion was associated with accelerated evolution of specific genes, Dorus and colleagues (Accelerated evolution of nervous system genes in the origin of Homo sapiens Cell 119, 1027-1040, 2004) compared the rates of evolution of 214 genes that have important roles in the central nervous system (CNS) in two different lineages: 1) a primate lineage between macaques and humans and 2) a mammalian lineage between rats and mice.
The average rate of evolution for these genes was much higher in the primate lineage than in non-primate lineage. Then the authors compared a subset of genes important for the CNS development and found a greater difference in the rate of evolution between rodents and primates than did the larger set of nervous system genes.
Dorus’ team also compared the lineage that led to humans with that leading to macaques and found that in humans CNS development genes have evolved fastest of all.