For the first time, scientists have produced monkeys composed of cells taken from separate embryos.
The animals were born after researchers combined cells from different embryos and implanted them into female monkeys.
Such animals, which contain genetically distinct groups of cells from more than one organism, are called "chimeras".
A US team, which has reported its work in the journal Cell, says the advance could have "enormous" importance for medical research.
Chimeras are important for studying embryonic development, but research has largely been restricted to mice.
The rhesus monkeys, which are normal and healthy, are made up of a mixture of cells representing as many as six distinct individuals.
"The cells never fuse, but they stay together and work together to form tissues and organs," said co-author Shoukhrat Mitalipov of the Oregon Health and Science University in Portland, US.
bbc.com
