A few hours ago, the UK Human Fertilisation and Embryology Authority (HFEA) made a landmark decision to grant scientists in London permission to genetically edit human embryos.

Thanks to the new licence, scientists at the Francis Crick Institute will be able to use a system called CRISPR/Cas9 (which is like an IRL copy-and-paste tool for DNA) to modify the genes of developing embryos, with the goal of improving IVF success rates and reducing miscarriages.

This is the first time a national regulatory body anywhere in the world has given the procedure the green light, and it's a huge day for science. But the move has also sparked a lot of concern about the creation of designer babies.

So what does it really mean for society? We've broken down the facts, so you can share them with your concerned parents and coworkers.

1. Genetically editing humans isn't suddenly 'legal' in the UK

Only one group of scientists, led by molecular biologist Kathy Niakan, has been given permission to use CRISPR/Cas9 on human embryos, for the sole purpose of better understanding human embryo development. No one else has permission to use the technique in the UK (or anywhere else in the world, although some countries are less regulated - see point 8).

2. The embryos used in the experiments will come from donors

The research team will be working on embryos donated by women who have previously undergone IVF and have excess embryos.

3. Don't worry, nothing's happening without ethics approval

"The committee has added a condition to the licence that no research using gene editing may take place until the research has received research ethics approval," explained the HFEA in an emailed statement, as reported by Motherboard. That means the researchers now have to go through a separate ethics approval process before they can start research on human embryos - they don't just automatically have permission to do whatever they like.

4. The embryos won't be brought to term

The researchers only want to examine the effect of different genes on the first seven days of embryonic development, when the embryo goes from having one to around 250 cells. The new license also states that the embryos need to be destroyed within 14 days, and can't be implanted into a woman.

5. This work could finally reveal how a healthy human embryo develops

This is something that's still poorly understood in the world of molecular biology, and could help scientists to improve IVF and prevent miscarriages. As the BBC reports, out of every 100 fertilised eggs, fewer than 50 reach the early blastocyst stage, 25 implant into the womb and only 13 develop beyond three months.

"The reason why it is so important is because miscarriages and infertility are extremely common, but they're not very well understood," said team leader Kathy Niakan.

6. Experts are calling the decision a "victory for level-headed regulation over moral panic"

While there are still concerns about genetic editing, this first, highly regulated step has been labelled by some scientists as "a triumph for common sense". 

"It is a clear example how the UK leads the world not only in the science behind research into early human development but also the social science used to regulate and monitor it," University of Kent geneticist, Darren Griffin, told AFP.

7. But critics are worried that we're on a path towards designer babies

Let's face it, there are definitely big ethical questions to be answered going forward. At the end of last year, a UNESCO panel of scientists, philosophers and lawyers called for a halt on genetic editing until it's better understood what affect it would have on heritability and the human germline. And today's decision was met with concern by some groups.

But the license in this case is extremely limited in its scope, and it's still illegal for ANYONE to implant genetically modified babies into women, or bring them to term, so we're a long way off any of these scenarios.

8. This isn't the first time that human embryos will be genetically modified

Last April, Chinese scientists admitted to tweaking the genes of 28 embryos to try to prevent a deadly blood disorder. They encountered serious challenges in their research, and said the technology has a long way to go before it can be used to treat disease in humans.

9. Still, CRISPR/Cas 9 is a really big deal

CRISPR/Cas9 has been heralded as the biggest biotech discovery of the century. The system works by using the Cas9 enzyme to cut human DNA, which means scientists can either snip out damaged genes, or insert new ones. Although it's not perfect, the technique incredibly simple and adaptable compared to gene editing tools that have been trialled in the past.

Since its development in 2012, it's shown great promise in being able to treat conditions such as vision loss, muscular dystrophy, and even drug-resistant superbugs. If it works in humans, the technique could quite literally change everything. 

10. There's no sign of gene editing being allowed in human embryos in the US any time soon

Last year, the US National Institutes of Health made it clear that it wouldn't be allowing scientists to edit human embryos any time soon, stating that it "will not fund any use of gene-editing technologies in human embryos".