"Stearns says globalization, immigration, cultural diffussion and the ease of modern travel will gradually homogenize the human population, averaging out more and more people's traits. Because recessive traits depend on two copies of the same gene pairing up in order to get expressed, these traits will express themselves more rarely, and dominant traits will become the norm. In short, blue skin is out. Brown skin is in.
Already in the United States, another recessive trait, blue eyes, has grown far less common. A 2002 study by the epidemiologists Mark Grant and Diane Lauderdale found that only 1 in 6 non-Hispanic white Americans has blue eyes, down from more than half of the U.S. white population being blue-eyed just 100 years ago."
I wonder, perhaps related mechanisms could explain why humans may be getting dumber (if it is true that we are), and if so, how we could have gotten dumber so (relatively) quickly - e.g.:
"Dr. Gerald Crabtree from Stanford University writes in the journal Trends in Genetics that humans have been steadily losing intelligence for thousands of years"