> A handful of girls seem to defy one of the biggest certainties in life: ageing. He has identified four girls with this condition, marked by what seems to be a permanent state of infancy, a dramatic developmental arrest. He suspects that the disease is caused by a glitch somewhere in the girls’ DNA. His quest for immortality depends on finding it.
The key is that the mutation would prevent reproduction. If you never age, you never reproduce.
You can think about different cancers. A mutation that causes fatal childhood cancer doesn't get passed on. A mutation that causes prostate cancer can spread.
Aging is weird. Maybe there’s something to be learned from these cases, but it’s very unlikely to be straightforward. Unless you’re a roundworm. We can make those live hundreds of human-relative years. But in those cases it’s a tiny number of genes involved, we have near zero evidence that the same is the case for higher organisms.