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.