I'm no biologist - but could it be that this hormone is some evolutionary artefact - a holdover from some ancient common ancestor - that we can now do away with completely? If the evidence in mice shows that blocking the ageing process showed no real 'negative' consequences, then does this suggest that we might simply block the effects in humans completely? Or, as I suspect, is it more likely that there is some evolutionary advantage to ageing in the 'normal' way?