US biologists have created cloned monkey embryos, and successfully transferred them into monkey mothers. Although none of the resulting pregnancies lasted more than a month, this is by far the closest scientists have come to cloning a primate.

If researchers are able to repeat this process in monkeys, it might help them to refine the tricky technique without experimenting on human eggs and embryos, which are very difficult to obtain and raise a host of ethical objections. This in turn might help to resolve whether human embryonic stem cells, which can grow into a variety of tissues, will prove useful in medicine.