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Speaking of radiation resistance, species such as Deinococcus radiodurans (bacteria) and Thermococcus gammatolerans (archaea) can survive doses in the 15-30 kGy range. They have evolved incredibly efficient DNA damage repair to handle the high rate of double strand breaks (DSBs) associated with such conditions.

What is interesting is that these high radiation doses don't really occur naturally to the point where such mechanisms would have evolved and then been maintained. Instead, it is believed that they evolved to confer resistance to desiccation, which also induces DSBs at a similar rate.