Die hohlen Zellkugeln gleichen sechs Tage alten menschlichen Embryonen. | Photo: Monash University

More than half of all pregnancies terminate naturally in the first two weeks. But there are too few embryos available from reproductive medicine for scientists to investigate this early stage of human development. This is why there’s now a lot of hype in the science community about embryo models created from adult stem cells, as has been reported in the journal Nature. Researchers in the United Kingdom have developed new guidelines for this research. They don’t set any limits on how far these models may be allowed to develop, but they prohibit their being implanted in humans or animals. They also call for a licensing authority to be set up. Robin Lovell-Badge of the Francis Crick Institute has spoken out on the BBC in favour of these guidelines: “Hard laws often can be very slow to keep up with the science”.