Africa and DRD4

The DRD4 gene codes for a dopamine receptor in the brain. It exists in several versions, or alleles, and studies have shown that people tend to have slightly different personality traits depending on which they have. The 4R allele, for instance, is associated with being even-tempered, reflective and prudent. The less common 7R and 2R versions have been linked to impulsive and exploratory behavior, risk-taking and the ability to shrug off new situations. Researchers think that humans who migrated from Africa with these versions were better able to deal with dangerous, fluctuating situations and more likely to survive and reproduce under those conditions. They looked at the frequency of 7R and 2R in 18 indigenous populations spread along the routes humans took from Africa to Europe, Asia and the Americas. The further away from Africa they were, the more likely they were to have either of these two versions. Researchers are beginning to play with the idea that our culture could be influencing evolution. They have shown that 7R arose as a rare mutation 40,000 to 50,000 years ago, after the ancestors of Europeans and Asians left Africa, then spread rapidly. The 2R allele is a modified version that arose in Asia less than 10,000 years ago. The have also shown that people diagnosed with attention deficit hyperactivity disorder are twice as likely to have the 7R allele. Some of what we consider ADHD symptoms, like rapidly shifting focus and quick movements, may actually be survival traits that were selected for during the Eurasian migration out of Africa.