I ask because i recall reading that epidemiologists found survivors of hiroshima to be healthier than thos not exposed.
Which makes me wonder: is evolution at least partly driven by radiation-induced muations?
Or is their a simpler explanation (for the hiroshima survivors health)?
Well… you’d have to be pretty good at self healing to survive Hiroshoma, so I would say you have a selection bias. 
As I recall reading years ago, yes, a small amount of radiation tends to be good for you. The theory I’ve heard is that a small amount stimulates the body’s repair mechanisms to activate, but does so little damage they repair more damage than was caused by the radiation. Twice background level is ideal as I recall.
Although as a practical matter you don’t want to add radioactive material as nutritional supplements or anything like that; if you deliberately raise your exposure to the “ideal” level, you’ve also just eliminated any safety margin against further exposure.
As far as Hiroshima itself goes; it seems more likely to me that meara is right and the survivors were just the tougher members of the population, on average. The radiation produced by the bomb was well above the levels I was talking about above, and killed quite a few people.
You’re asking two completely separate questions: Does radiation drive evolution? and Did the Hiroshima survivors benefit from their radiation dose?
The answer to the second question is an unreserved NO.
The first is more interesting. Radiation does cause mutations, and evolution is driven by mutations, so, yes, evolution might have gone slower if there were no radiation around. The thing is, mutations are generally good for the population but bad for the individual. The vast majority of mutations are harmful to the individual, so if you’re the sucker that gets the dose, you’re probably screwed. There will be a few here and there that pick up something useful (as an aside, the odds of an organism as complicated as humans getting a beneficial mutation from something like a nuclear bomb are pretty much nil. Things are a little more subtle with us - more often, there’s something like gene duplication and divergence…anyway, I’m getting off track), but the ideal strategy for me is to have someone else experiment with the new genes, figure out what’s good, and then mate with me and give those to my kids.
Interestingly, there’s good evidence that when E. coli gets badly stressed, say with a dose of radiation, it turns on DNA copy machinery that makes an unusually high number of errors. The theory is that if you induce mutations, you might luck out and create a daughter cell that has whatever it takes to survive the crisis - sort of a deliberate accelerated evolution.
Ah, ever heard of sunlight? Radiation comes in all shapes and sizes. Well, energy states and sizes.
In reference to ionizing radation, this is known as hormesis. There is still a lot of debate in the Health Physics and medical community about it; there just isn’t enough reliable data at the low end of radiation exposure to draw any good conclusions as of yet.
The OP probably has a factual answer, (we may have already seen it), so I am going to move this non-debate question to General Questions.
Wouldn’t activating the repair mechanism shorten your life in the long run though? I thought your cells could only split and such so many times before they basically don’t work at full efficiency anymore. So while they may be healthier in the temporary, they’re leading shorter lives (however, this amount to only a day for all I know).
I don’t know how hard it will be to find a good online cite, but here’s the summary of the facts as I remember them.
People living around Hiroshima have been studied since the war. Those who lived far enough away had the same life expectancy as the general population of the area. Those who lived close to the bomb site lived a much shorter life expectancy. Both of these are expected. but there was a range of distance where people living there had a longer life expectancy, despite a slightly raised chance of leukemia.
This would be in line with the evidence in kidchameleon’s link to evidence of hormesis. There’s one more study not mentioned there, which is Navy shipyard workers from the 50’s. A study found that those whose job exposed them to the greatest amounts of radiation had the longest life spans.
Unfortunately, I’ve never seen any evidence for a mechanism for this, which casts a lot of doubt. Also it’s hard to eliminate other factors. For example, you can’t compare workers exposed to radiation to the general population, because those workers tend to have better incomes and health care. While I think the studies around Hiroshima have accounted for survivor bias, it could be something about the neighborhoods involved that accounts for the differences.
In my opinion, the answer to the OP is: maybe, but the effect seems to be small and needs more study.
ETA: site and cite are not the same thing. Oops.
As stated previously, this could also easily be explained as a selection bias. Ionizing radiation causes free radicals which lead to cancer and such. One person may have a better metabolism for dealing with free radicals than another. This will not only protect them from the radiation at Hiroshima, but also from standard aging mechanisms which often result from free radicals. Thus, the people that didn’t develop leukemia etc., also have a longer life expectancy.
It’s all speculation on my part though.
Most of the mechanisms proposed don’t involve cell death though; they’d be doing things like repairing cell damage. And those that do would be the ones that destroy mutant or possibly mutant cells, the ones that might turn cancerous, so you’d probably come out ahead. Assuming that the effect is real that is.
Well, it does help with Vitamin D
Brian
And to put this in a slightly broader historical context, arguments about hormesis not only predate 1945 by several decades, they originally had their origin in debates over chemical carcinogens. Furthermore, since the issue is usually closely tied to the issue of how we ought to regulate industrial exposures to low levels of the agent in question, there’s usually at least been some political undertones involved.
In other words, it’s not a new debate and it’s always been a messy one.
Cancer Wars (Basic Books, 1995), by the historian of medicine Robert Proctor, is partly about tracing the origins of the debate.
While I agree that this one data point might be explainable as selection bias, all the studies together make a compelling case. I found the studies that showed exposure to household Radon decreased the incidence of Lung Cancer particularly interesting:
http://www.sciencedaily.com/releases/2008/03/080325122807.htm
But I’m still not sure the evidence is enough to expose yourself to extra radiation on purpose, which google does find a few pages recommending. It does support worrying a little less than most people do about radiation, though.
As others have noted, the discussion should examine ionizing radiation to answer Ralph’s intended question.
I’d say that infrared radiation producing an ambient environment with a blackbody radiation at about 300 K, and with infraviolet/ultrared radiation of a certain number of lumens during rougly half the diurnal cycle, is essential to life as we know it. But that, of course, is not ionizing radiation.