Editing embryo DNA is an exciting landmark, but in reality will benefit few

Even if legal barriers were lifted, the conditions genome editing would help are rare, and our understanding of genes is still too poor for it to be widely used

It is hard to overstate the importance of the moment. For billions of years, life on Earth has been shaped, slowly and incrementally, by dumb evolution. But in research this week, scientists showed how that might change. With advanced genetic engineering tools, a US-Korean team mended dangerous heart disease mutations in human embryos for the first time. The feat paves the way for radical new treatments - and for humans to take control of their genetic destiny.

The ability to edit human genomes may one day transform people's lives, but in breaking new ground, it would cross a line that has long been controversial. Today, many countries prohibit the creation of genetically altered people, even if the procedure would spare them a devastating and life-shortening disease. The caution comes from the fact that changes to an embryo's DNA affect not only the child in question, but their sperm or eggs. When the time came, they would pass on the modifications - and any harmful side-effects the procedure may cause - to their children and future generations.