Two studies suggest that the human brain continues to change through the process of evolution. The findings conflict with a common belief that the brain has evolved about as much as it ever will.
Scientists say modern humans developed about two hundred thousand years ago. Bruce Lahn of the Howard Hughes Medical Institute and the University of Chicago led the studies. The findings appeared in Science magazine.
Scientists looked at changes in two genes related to the size of the brain. These two genes do not work right in people with microcephaly. Microcephaly is a rare condition in which people are born with a brain that is much smaller than normal. Some scientists believe this is what the brain of early humans might have looked like.
In the new studies, the scientists looked at different versions of the two genes. They studied genetic material from people of different ethnic groups. They found that one version of each gene appeared again and again. The scientists say the changes appear to have spread because they improved the brain in some way. They say the new versions are so common, they cannot be considered an accident.
Instead, the scientists suggest there was pressure to spread through natural selection. Natural selection is a process in which genetic changes that are helpful to a species survive and spread quickly.
The scientists found that the new versions of the two genes evolved much faster in apes than in mice and rats. They decided that these changes might have had an important part in human evolution. The scientists studied how often the changes appeared in the genes of many different populations.
They found that a version of the gene called Microcephalin formed only about thirty-seven thousand years ago. This version appears today in about seventy percent of humans. The scientists say it is more common outside of southern Africa.
The second gene is called ASPM. The studies showed that a version of this gene developed just about six thousand years ago. Today it is found in about thirty percent of all people. It is more common in people from Europe and areas including North Africa, the Middle East and South Asia.
Different populations make use of different genetic changes. Genes must react to the pressures of many environments and threats such as disease. The scientists who did the studies now want to see if the two genes only act on brain size or also perform other duties.
They point out that the genetic changes took place around the same time as important cultural changes. These include the development of things like art and religion and, more recently, civilizations.
Scientists do not know, however, if the two genes are connected to intelligence or problem-solving abilities. Such questions about the mind produce debate. Some scientists are concerned that the new findings might be used to claim that not all groups are created equal.