Twins Roku and Hex are the world’s first chimeric monkeys, who have been created with genetic material from six “parents” at Oregon Health and Science University in the U.S.

The monkeys’ birth has caused an ethical storm, with critics accusing scientists of disregarding the welfare of the animals.

Named after the fire-breathing creature in Greek mythology composed of parts of multiple animals, chimeras are organisms made up of cells from two or more genetically distinct sources.

Twins Roku and Hex, whose respective names come from the Japanese and Greek for “six”, have been created with genetic material from six monkeys.

Researchers extracted cells from six macaque embryos and combined them into a single embryo in a laboratory before implanting it into a surrogate mother monkey.

Twins Roku and Hex are the world’s first chimeric monkeys, who have been created with genetic material from six “parents” at Oregon Health and Science University

Three male babies were born using this process – Roku and Hex, who are twins, and Chimero.

However, to reach this stage, dozens more embryos were experimented on, and some surrogate pregnancies were aborted.

While most animals only contain cells in which the genetic material from their two parents has mixed together, the chimeric monkeys’ bodies contain six different types of cell – holding distinct DNA from each biological parent.

Although many mice and some rabbits, rats and farm animals have been born this way, no one has created chimeric monkeys before.

The researchers say that Roku and Hex are healthy and that their birth opens up “enormous” possibilities for science because of monkeys’ intelligence and close biological links to humans.

They say the technique could help us learn more about IVF and contraception, and growing human organs from scratch.

Critics of the study, published in the journal Cell, say that techniques such as these take a high toll on animal welfare and question what sort of experiments the monkeys will be put through in future.

The British Union for the Abolition of Vivisection (BUAV) called the research “deeply disturbing”.

Dr. Jarrod Bailey, the organization’s scientific consultant, said: “Using such highly sentient animals in this research raises enormous ethical concerns and imposes a heavy welfare burden, resulting in severe suffering to many animals.

“As few genetically modified animals show the <<desired>> characteristics, many will be killed even before any research can take place, while others will die of severe and unrelated malformations caused by the genetic modifications.

“The monkeys who do exhibit characteristics of ‘interest’ are destined to suffer greatly by their very nature, and via the experiments to which they will be subjected.

“The cells never fuse, but they stay together and work together to form tissues and organs,” said lead scientist Dr. Shoukhrat Mitalipov, from the Oregon National Primate Centre.

“The possibilities for science are enormous.”