Micro-RNAs block messenger RNA that translates DNA into protein, which refines genetic makeup, NewScientist.com said. Since its discovery a few years ago, micro-RNA has been found to determine a gene's expression, or how its DNA sequence is converted into structures and functions.

Researchers at the Hubrecht Laboratory in Utrecht, the Netherlands, compared RNA in human and chimp brains, finding 447 new micro-RNAs, Newscientist.com said. The number researchers found is more than doubled the number of micro-RNAs discovered so far. Team member Edwin Cuppen said researchers observed that while many micro-RNAs were found in chimps and humans, some were found only in humans, Newscientist.com said. Based on the findings, Cuppen said researchers said they believe small genetic changes that fine-tune a gene might account for the radical differences in human and ape brains.

Cuppen also said researchers think micro-RNAs could be why the human brain has 10,000 cell types, WebMD.com said.