Smaller Brains in Contemporary Humans

As social complexity has increased, brain size has decreased. Indeed, this article argues that there has been a significant decrease in brain size in humans -- which probably signifies the brain is becoming more efficient. Of course, it could mean that it is becoming denser, which would result in more complexity -- something we see in cities, for example. What implications might this have for theories of human intelligence and behavior that seem to rely on a relatively unchanging human nature for the past 10,000-30,000 years? Might we expect some changes in behavior with such increases in density and/or decreases in brain size?