- The human brain has decreased by about the size of a tennis ball over the past 30,000 years.
- Evolution may be making our brains leaner and more efficient.
- The same phenomenon can be observed in domestic animals compared to their wild counterparts.
Human brains have shrunk over the past 30,000 years, puzzling scientists who argue it is not a sign we are growing dumber but that evolution is making the key motor leaner and more efficient.
The average size of modern humans -- Homo sapiens -- has decreased about 10 percent during that period -- from 1,500 to 1,359 cubic centimeters (91 to 83 cubic inches), the size of a tennis ball.
Women's brains, which are smaller on average than those of men, have experienced an equivalent drop in size.
These measurements were taken using skulls found in Europe, the Middle East and Asia.
"I'd called that a major downsizing in an evolutionary eye blink," John Hawks of the University of Michigan told Discover magazine.
But other anthropologists note that brain shrinkage is not very surprising since the stronger and larger we are, the more gray matter we need to control this larger mass.