Researchers in the US have successfully produced baby monkeys using cells from multiple embryos for the first time.
Three rhesus monkeys were born at the Oregon Health and Science University following the procedure, which involved combining two or more fertilised eggs into a single embryo and implanting them into females to create so-called 'chimera' creatures.
The male primates – called Chimero, Roku and Hex – were developed from cells originating in as many as six distinct genomes and are said to be healthy.
Researcher Shoukhrat Mitalipov explained: "The cells never fuse, but they stay together and work together to form tissues and organs."
He added: "The possibilities for science are enormous", as it is thought the technique will give scientists a better understanding of stem cell developments, which could lead to better treatments for a range of human diseases.
However, the experiment has proved controversial, with the British Union for the Abolition of Vivisection's science adviser Dr Jarrod Bailey saying the use of highly sentient creatures raises "enormous ethical concerns".