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Tardigrades are odd little animals. They are quite small, the largest species measuring about half two millimeters long when fully grown, but are more typically about a half-millimeter long. They are commonly called water bears. They are in a phylum all by themselves, an evolutionary thread all their own; they not directly related to arthropods (insects or spiders), vertebrates (fish, reptiles or mammals), or even the various kinds of worms. They have a segmented body with eight legs. They’re not terribly pretty, but as a group, they have evolved to survive in environments that would easily kill the rest of us. From Wikipedia:
Tardigrades are among the most resilient animals known,[11][12] with individual species able to survive extreme conditions – such as exposure to extreme temperatures, extreme pressures (both high and low), air deprivation, radiation, dehydration, and starvation – that would quickly kill most other known forms of life.[13] Tardigrades have survived exposure to outer space.
So why is it so hard to kill a tardigrade? What mechanisms exist in their DNA and their biology that allow them to survive in conditions where all other creatures would perish? A new paper authored by Chinese scientists addresses one aspect of this question: How do tardigrades survive large doses of radiation? The subject of this study was a new species of tardigrade discovered in the Henan province of China, Hypsibius henanensis.
High energy radiation, such a gamma rays, typically damages DNA (as well as other biomolecules) by ionizing the atoms that make up the molecule, creating what are called radicals (molecules with unpaired electrons), which are extremely reactive. In most species, such radiation can damage the double helix structure of DNA, which can result in some forms of cancer.
The tardigrades in this study appear to have three strategies stored in their genome that combat such damage due to radiation. First, they produce a protein called TRID1, unique to tardigrades, that quickly repairs DNA damage due to ionizing radiation. Second, after radiation expose, a gene is switched on that produces two proteins that, under normal circumstances, are important in the production of mitochondrial ATP (the molecule that is the energy currency of all life on Earth), but also play a role in DNA repair. Third, radiation exposure stimulates the production of proteins whose job it is to scavenge free radicals before they can do any damage.
So even if the human race destroys itself, there will still be life on Earth capable of surviving whatever horrific conditions our actions have produce, be it nuclear weapons or the consequences of unrestrained climate change.
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In Thunderthief's diary about the war in Ukraine. Mr Completely (here), jdeming (here), and Uberbot (here) discuss Russia's centuries long indifference to human life.
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