A group of Chinese scientists from Kunming Institute of Zoology, Chinese Academy of Sciences, and the University of North Carolina in the US have successfully transplanted human brain genes into rhesus monkeys. This experiment was carried out to shed light on the evolution of human intelligence as these genes, or MCPH1s, are believed to play an essential role in human brain development. In the experiment, eleven monkey embryos were injected with a virus carrying the genes. Six monkey embryos died instantly, while the monkeys that survived were examined for memory and brain development with an MRI machine. The researchers found that, similar to human brains, the brains of the five remaining transgenic monkeys developed more slowly than the brains of normal monkeys. Moreover, compared to wild rhesus monkeys, the transgenic monkeys scored better and responded faster in short-term memory tests. The transgenic monkeys generally behaved similarly to normal monkeys and have a similar brain size. These findings thus support the idea that the longer brain development period of humans may account for superior intelligence when compared to animals. In addition, the research helps advance knowledge about human evolution.