In his time-travel musings to mark Doctor Who's half-centenary, Andrew Jaffe overlooks one facet of the Gallifreyan narrative: regeneration (Nature 502, 620–622; 2013). Rather than die, time lords can choose to regenerate (purportedly up to 12 times) once their bodies are worn and weary.

Even though time travel is still in the realm of fantasy, progress in the sphere of rejuvenation is palpable. Many of the disagreeable features of ageing are now successfully countered by medical science and technology.

The Doctor would surely advise us to focus more closely on preventing degeneration, especially in light of the boom in life expectancy over the past 50 years and its accompanying social and scientific challenges.