Humans and Chimps share 98.5% of their genes. However, no one would say that chimps approach humans in intelligence or cognitive ability.
What accounts for the difference?
About 5 million years ago or less, a genetic change was introduced into a protein called the neuropsin, which governs memory and learning and is found only in neurons in the central nervous system. While both humans and chimps have neuropsin - humans alone have a second form of the protein called Type II neuropsin. It is disintinguished from the former in that it is 45 amino acids longer.
In the recent study, conducted by Dr. Bing Su at the Chinese Academy of Sciences and just published in the journal Human Mutation, scientists also showed that inducing the Type II mutation in chimpanzee neurons was sufficient to create the longer splice variant found in humans, demonstrating that a relatively minor mutation could account for the difference in protein length - and therefore the mental performance gap, between the species.
It would be interesting to determine if the genesis of the Type II variant led to the development of consciousness or enhanced self-awareness by stimulating changes in the brain.