Genes and brain size

Science magazine reports that "two genes involved in determining the size of the human brain have undergone substantial evolution" as recently as 5,800 years ago.  Those two genes are microcephalin and ASPM.  When those genes are completely switched off, they lead to "microcephaly", or small head.

Another gene, GPR56, appears to affect mainly the development of the frontal cortex.  According to Wikipedia, the "frontal lobes have been found to play a part in impulse control, judgment, language, memory, motor function, problem solving, sexual behavior, socialization and spontaneity. Frontal lobes assist in planning, coordinating, controlling and executing behavior."

With this knowledge, scientists investigated whether different variants of the genes were responsible for different brain sizes among people.  According to the New York Times:

About 70 percent of people in most European and East Asian populations carry [a specific variant of the microcephalin] gene, but it is much rarer in most sub-Saharan Africans.

With the other gene, ASPM, a new [variant of the gene] emerged 14,100 to 500 years ago, the researchers favoring a midway date of 5,800 years. The allele has attained a frequency of about 50 percent in populations of the Middle East and Europe, is less common in East Asia, and is found at low frequency in some sub-Saharan Africa peoples.

The Chicago team suggests that the new microcephalin [gene variant] may have arisen in Eurasia or as the first modern humans emigrated from Africa some 50,000 years ago. They note that the ASPM [variant] emerged about the same time as the spread of agriculture in the Middle East 10,000 years ago and the emergence of the civilizations of the Middle East some 5,000 years ago, but say that any connection is not yet clear.