ALEX COMFORT 
the release of radiation by psychopaths in the course of bomb- 
testing cannot be ignored. It has so far contributed a much 
smaller amount than the individual dose which we receive in 
civilized countries with busy X-ray departments, but it may 
well eventually contribute more to the dose received by the 
human genome as a whole. We still do not know whether 
low-dosage radiation really accelerates ageing. It may do so, 
or it may only simulate an acceleration of ageing by reducing 
vitality in some way unrelated to the normal ageing process. 
If ageing is accelerated we should expect animals that die 
earlier than usual after low-dose irrradiation to do so from 
approximately the same causes in approximately the same order 
as their unirradiated littermates. Lindop and Rotblat have 
recently shown that in general they do die from the same causes, 
but not in exactly the same order. 
We do not as yet know whether the study of radiation effects 
will prove to be the key to the normal ageing process or simply 
a mischievous diversion of energy, nor is it at all clear what 
law of equivalence relates the life-shortening effect in rats and 
mice to that in larger animals and man; that is, would the 
equivalent dose which reduces the two-year life of a mouse by 
three months reduce human life by three months (which would 
be nearly undetectable actuarially), by a quarter, by some other 
amount, or not at all? A claim of a significant radiation effect 
on the longevity of radiologists in America has not been con- 
firmed in a later study of English radiologists from 1897 to the 
present day. We have no life-tables yet for people who live in 
areas with a high background of radioactivity. Whether 
politicians have already shortened our lives by exposing us to 
increased background radioactivity and unanticipated local 
concentrations of isotopes, whether our physicians shorten them 
even more by the use of diagnostic X-rays, and, if so, by how 
much, nobody yet seems to know. Caution seems necessary, 
because the effects could conceivably be large, and for this 
reason it may be politic not to speak too loudly of any possible 
gain in longevity from mutation-induced heterosis in man, 
though that too is a possibility. 
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