‘Injecting old mice with the blood of young mice produced a marked improvement in activity, strength and cognitive power.’ Photograph: Zoonar GmbH /Alamy

At last, news we can all use. American researchers in three separate tests have suggested that blood transfusions could rejuvenate not just dodgy cyclists but everyone. It could be a giant step in the quest for immortality, a quest as old as humankind itself. Why wait for Darwinian natural selection when the blood bank can shorten the process by millennia?

Back in time, popes and monarchs wondered if drinking the blood of the young might improve their valour in battle, or their longevity. No shred of evidence supported them. Today it appears that injecting old mice with the blood of young mice produced a marked improvement in activity, strength and cognitive power. A mouse wakes up feeling a whole new mouse.

Since blood transfusion has long been medical practice, its restorative effects are hardly surprising. Oxygenated blood has long been used by sportsmen, as have other performance-enhancing substances. Surgeons can hardly be surprised that anaemic patients feel better with a few pints of fresh blood in them. Indeed it is curious that, with millions walking around with younger people's blood in them, no one has thought to test whether they live longer and more fulfilled lives.

Nonetheless the possibilities are clearly sensational. Advances in embryology and stem-cell research have already hinted at the huge possibilities in genetically improving the human body. Appalling conditions are being rendered extinct and only the most reactionary fundamentalist could object. That such steps should one day embrace the ageing process is understandable. Even so, medical practice must keep abreast of ethics, which is another way of saying it must always take care of public consent.

Moving from preventing diseases to tinkering with the life cycle of healthy but ageing people hints at the notorious "step too far". It is an obstacle against which the science of the human body has always had to struggle. But in science there is no such thing as a step too far, only a step that has been ill-considered and ill-regulated. This must be an exciting breakthrough. Reactionaries must console themselves that it may work only for mice.