Three scientific teams published separate studies on Wednesday showing that embryonic stem cells can be made by reprogramming some of the genes in adult skin cells, without having to create an embryo – at least in mice.

Separately, a fourth scientific paper showed that newly fertilised eggs could be used instead of unfertilised eggs to produce cloned mice. If this technique were extended to humans, it might open up a new source of stem cells for therapeutic cloning research: frozen ­early-stage human embryos, which are much more plentiful than human eggs.