If people take multiple IQ tests over the years, they can see whether or not the quality of their cognitive function is improving or declining with age. While mankind on the whole cannot take an IQ test, if it did, Stanford University's Gerald Crabtree would say humans are losing their intellectual abilities.

This is the hypothesis Crabtree proposed in a paper that was recently published in the Cell Press journal "Trends in Genetics." According to Crabtree, not only are humans losing their intellectual abilities, but those related to emotion as well. These changes may be the result of gene mutations. Crabtree said that between 2,000 and 5,000 genes are necessary for there to be intellectual ability. However, two or more mutations have developed within the past 3,000 years that pose a risk to people's intellectual capabilities.

If Crabtree's hypothesis is correct, people should not panic about waking up one morning without any intellectual ability.

"I think we will know each of the millions of human mutations that can compromise our intellectual function and how each of these mutations interact with each other and other processes as well as environmental influences," Crabtree said. "At that time, we may be able to magically correct any mutation that has occurred in all cells of any organism at any developmental stage."