...when these animals dehydrate in response to environmental exigency, their DNA breaks into fragments, after which it is reconstituted upon rehydration. All species possess some capacity to repair errors in their genome; those individuals incapable of this maneuver will have been selected against, simply given the unavoidable tendency of DNA to mutate, even without the extra challenge of adjusting to extreme conditions. As tardigrade genes reconstitute themselves from the tun state, their cell and nuclear membranes become leaky, whereupon they might have acquired the habit of incorporating various pieces of non-tardigrade DNA which are inevitably floating around. Although presumably the stitching in of extra-specific DNA is initially random, it is entirely possible that some of these genomic additives were especially likely to contribute to their possessor’s fitness, whereupon they were projected into future generations, a process made all the more likely under conditions of fluctuating environmental harshness. If so, then one consequence of tardigrade adaptation to extreme conditions—for example, the ability to close down their metabolism and suspend normal DNA structure—will itself have contributed to their ability to adapt to those conditions, by facilitating the incorporation of those occasional DNA snippets that enhance survival and reproduction.
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