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Humanity has been exposed to prolonged nuclear radiation for thousands of years. In the past, hundreds of nuclear bombs dropped; then nuclear warfare ceased for thousands of years. Assume that humans survive for thousands of years with constant exposure to nuclear radiation. They have developed improved bodies that handle the radiation. Now, humans are extremely resilient to nuclear radiation, but it has been years since that last massive exposure to nuclear radiation.

What happens now when a nuclear bomb is dropped? Would they still be affected by the nuclear radiation with their evolution-improved bodies? Or would they still be subject to radioactive fallout? (Yes, many would be killed by the initial explosion, but would the following nuclear radiation have any substantial effect?)

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    $\begingroup$ One thing that you should note is that a nuclear bomb doesn't actually leave behind THAT much radiation as people imagine. It uses all that energy to create the explosion and destruction and left over radiation is energy that isn't fully used. A more reasonable weapon would be a something like a dirty bomb, a high explosive meant to distribute radioactive materials for the purpose of causing lasting hot spots that would be unlivable to us. A good example of this is looking at Hiroshima compared to Chernobyl. $\endgroup$ – Virusbomb Feb 28 '17 at 16:15
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    $\begingroup$ This question strongly resembles "how would humans evolve to be bulletproof", there is a very fine line between unaffected, and dead. Radiation does a number of different things, mostly tissue damage, one of the the issues you get early on is sterility. Sterility precludes any evolutionary participation. $\endgroup$ – Seeds Feb 28 '17 at 18:15
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    $\begingroup$ Humans (and all other life) HAVE been exposed to continuous nuclear radiation since the beginning of life. When you drop nuclear bombs, what mostly kills people is either being vaporized, or hit by the blast wave. And contrary to Virusbomb's example, people do live in the so-called 'Dead Zone' around Chernobyl. $\endgroup$ – jamesqf Feb 28 '17 at 19:42
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The effect of nuclear radiation is not fully understood in real life, so it would be hard to extrapolate to your rather interesting world. The current theory is that chronic radiation exposure is cumulative, accumulating through your entire life. There is also a concept of "acute radiation syndrome," which is what happens when your body receives a sudden influx. They start roughly around 100 rad and progress in lethality up to around 1000 rad (a few conversions suggest that 100 rad is roughly 20 years worth of permitted radiation for those who work with radioactive materials). Above that point, people just die. Nuclear weapons can release a large amount of radiation up front, so this may cause acute radiation syndrome no matter how much your humans were used to radiation.

Now the real question is how your humans protected themselves against radiation. A few thousand years, evolutionally, is a blink in time. It's virtually nothing at all. It is highly unlikely that we would evolve meaningful anti-radiation protections over a few thousand years, even in such a hostile world. We would more than likely just die. If we did develop a protection, it would be impossible to answer your question because how we end up protecting our genome will matter greatly. Without you specifying exactly what chemical mechanism is being used, we can't really help there.

There are some interesting edges to explore here. One key unknown in radiation studies is the effect of small doses on the body. We know that the amount of damage done by medium to large amounts of radiation is directly proportional to the amount of radiation received. In fact, this is so linear that we have units like rem or seiverts which are designed to track cumulative radiation effects on the body. However, it is not yet known whether small amounts of radiation still have this linear effect, or if they are actually easier to repair. We just don't have the data. If they are indeed easier to repair, there may be a mechanism you can leverage here to repair larger errors. It's much easier to re-balance an existing system than to evolve a new one.

One solution we could look at is genetic manipulation. Perhaps humans decided to change themselves to be more radiation tolerant. We might put checksums into our DNA to help us correct for errors. Such checksum like systems exist in our body today, but they're organic constructs that are designed to do "just enough" to keep us growing and evolving. A synthetic checksum could lock down our genome far greater. However, this would also create its own issues worthy of a novel.

The other solution would be to simply hide in a hole. The easiest way to survive radiation for a thousand years is to simply go somewhere that the radiation isn't found, and stay there. In such a case, obviously a nuclear bomb would have its full devastating effect.

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    $\begingroup$ Great Answer! DNA checksums would handle the cancer and mutation issues very nicely. From there, all you would need to add is an increased healing rate to offset the direct physical destruction of the radiation. Something akin to how our body's currently handle the IR portion of sunlight. An ablative outer shell made of dense scales might also be useful as disposable shielding, keeping much of the radiation out, to ease the burden on the inner systems. $\endgroup$ – Henry Taylor Feb 28 '17 at 16:10
  • $\begingroup$ How does the human body fight off radiation exactly? Does it build up antibodies or something similar? If that is the case small doses would make the body handle larger doses correct? I'm not sure myself kind of a question if anyone knows that. $\endgroup$ – Dtb49 Feb 28 '17 at 16:20
  • $\begingroup$ @Dtb49 Most of the damage is not a big deal, but the important damage is that which is done to the DNA. When radiation hits DNA it can break the chain. We have proteins which are designed to detect DNA breaks (from radiation and otherwise) and repair them. Typically this repair is done perfectly, but every now and then multiple breaks occur and the systems we have can't figure out the right way to put them back together. $\endgroup$ – Cort Ammon Feb 28 '17 at 17:06
  • $\begingroup$ -1 I have to disagree with your first statement. The facts about long term health risks to nuclear weapons survivors are well know. After all, there is a pool of tens of thousands of nuclear weapons survivors available for study, with varying doses, and many studies there are. $\endgroup$ – kingledion Mar 1 '17 at 2:00
  • $\begingroup$ @kingledion We understand the large doses, such as those experienced by nuclear weapons survivors, quite well. What we don't understand are the small doses. The damage done appears to be proportional to the total radiation dose, but we haven't been able to make any controlled studies to explore the effect of smaller doses (such as day to day doses). Given that the OP explicitly mentioned that the humans have developed ways to handle that dosage, it is very possible that those approaches scale up this unknown region. $\endgroup$ – Cort Ammon Mar 1 '17 at 4:29
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You've heard the expression whatever doesn't kill us makes us stronger? Well, in some cases, what does kill a few of us, leaves the average of what's left of us stronger.

Consider a couple real-life examples, starting with MRSA (Methicillin-resistant Staphylococcus aureus). Some people got a staph infection, so the doctor gave them some form of penicillin to fight it. This killed a large fraction of the bacteria in those patient's bodies, and helped those patients fight off the infection. However, in each patient a handful of cells out of many thousands survived. And which cells were those? The hardiest ones. Those cells went on dividing, spread to new patients, and the process was repeated. Now we have whole strains of super bacteria.

Another example is mosquitoes. Look it up on any outdoors site, and somewhere it will tell you to wear a repellent containing N,N-Diethyl-meta-toluamide, also called DEET. However, outdoor people have been wearing this stuff for decades, and now there is increasing evidence that some mosquitoes are able to ignore it. It is not clear if the same idea was at play, i.e. that sensitive mosquitoes went hungry and died, and the more resistant mosquitoes had a meal, bred, and passed on their resistance. Nevertheless, DEET may be soon be singing its swan song.

For your story, I suggest taking a similar approach. The early exposures do in fact weaken or kill many people, leaving only the strongest and hardiest available to breed. The cycle repeats over a handful of generations, until you have virtually impervious homo superior.

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As other people have pointed out, there isn't a lot of radiation after the blast. There is some so that would mean that the survival zone would be closer to the blast and there would be a lower incident of radiation sickness and cancer outside the "kill zone."

The heat and shock wave would still kill the same number of people. If there were enough bombs, nuclear winter would still kill off the crops and cause widespread starvation. But, on the plus side, there would be less of a cancer increase after.

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