I assumed from the headline that this would be a stupid article, but I took the time to read it anyway and found that this assumption was wrong.
The premise sounds quite solid: The unique challenges of being a flying mammal require spending lots of energy. Which leads to lots of free radicals. Which leads to lots of DNA damage. Which increases selective pressure for DNA repair.
Evolution normally doesn't select for organisms that are able to survive aging, because, from the standpoint of natural selection, once your reproductive years are past, your survival doesn't matter.
That aging resistance would be an incidental benefit of general DNA repair mechanisms that evolved in response to a lifestyle that encourages free radical formation makes a lot of sense. The specific molecules and reactions involved in bats probably will provide important clues to the aging process in mammals, even if the adaptations in bats can't be translated directly into treatments for humans.
How immunity and disease fits into this picture is less clear from the article. But the aging angle alone is enough to make this research very interesting.
> Evolution normally doesn't select for organisms that are able to survive aging, because, from the standpoint of natural selection, once your reproductive years are past, your survival doesn't matter.
The logic is actually a bit deeper than this. There's no reason you couldn't have an organism that "survived aging", and that could reproduce indefinitely. Obviously, given a potentially unlimited reproductive span, selection would come in on the side of longer lifetimes.
As I've seen it presented, the logic of organism deterioration with age is that accidents happen, which means that, if you happen to have a life strategy which makes you momentarily better off, but permanently worse off, you may die of unrelated causes before suffering a net loss. As long as that can happen, we should observe aging: young organisms boosting their performance at the expense of their own future selves.
(as an example: imagine you impress a girl by doing some death-defying stunt, and suffer more physical strain than your body is really designed for. If you were going to live forever, that might be a bad idea. If you're not, then maybe impressing the girl is worth the lower physical fitness you have afterwards.)
> if you happen to have a life strategy which makes you momentarily better off, but permanently worse off, you may die of unrelated causes before suffering a net loss
This is true, but irrelevant to the present discussion. If you can live and reproduce forever -- or for a very long time -- then the -EV of "permanently worse off" exceeds the +EV of "temporarily better off."
My understanding of why we didn't evolve to have better gene repair and longer lives is that the ideal death and mutation rates in terms of species survival is some finite number greater than zero. Near-immortality, eternal youth and perfect genome repair would be great from an individual perspective, but from a species perspective, those things reduce the ability for genetic innovation. Too many mutations are bad, but not enough mutations are also bad.
I would guess that the bats get around this by getting so much extra EV from occupying the unique ecological niche of "flying mammal" that the ability to occupy that niche overwhelms the negative aspects of a smaller mutation rate.
>I would guess that the bats get around this by getting so much extra EV from occupying the unique ecological niche of "flying mammal" that the ability to occupy that niche overwhelms the negative aspects of a smaller mutation rate.
You're assuming a smaller mutation rate. The article points out that bats generally don't live to die of old age, something else usually gets them first.
A longer theoretical lifespan doesn't reduce the mutation rate if lifespans in practice are still modest. (If the first couple of hits on Google are any indication, bats typically live for a couple of decades.)
They aren't. The article says: "For an animal of their size, [bats] also age very slowly..."
I'm assuming that, without their gene repair mechanism, they would have been more in line with other animals their size, and occasionally died of old age. So the gene repair mechanism does extend the bats' lifespan.
To do good science, of course, you'd have to confirm this by an experiment to raise some bats that lack the gene repair mechanism and measure their deaths due to old age against a control group. Or better yet, do a fantastically expensive long-term experiment comparing bat colonies with and without the DNA repair mechanism, and measure their genetic drift over time.
Of course, I haven't done those experiments. If someone else does them, and shows results contradictory to my assumption, it'll be a great scientific discovery. But in the absence of evidence to the contrary, it seems like it's a safe bet that the DNA repair mechansim would reduce mutation rates on its own, and anything that makes the bats live longer would also reduce mutation rates on its own, and having both longevity and DNA repair together would reduce mutation rates at least as much as either by itself.
You may say decades of lifespan is "modest" by human standards, but much more relevant comparisons would be to bats without the DNA repair mechanism -- or, if data is lacking on those, to closely related mammals of similar size.
> My understanding of why we didn't evolve to have better gene repair and longer lives is that the ideal death and mutation rates in terms of species survival is some finite number greater than zero. Near-immortality, eternal youth and perfect genome repair would be great from an individual perspective, but from a species perspective, those things reduce the ability for genetic innovation.
If this is the dominant effect in how organisms deal with aging, it can explain why we observe aging all around us in the world, but it predicts that, if you track a population over time, you will see lifespans creeping steadily upward. I don't believe this is actually observed.
The phenomenon you describe is generally invoked to explain sexual reproduction. But it is not unheard of for a particular ecological niche to be dominated by a clonal organism; it's just that those clonal organisms sometimes (inevitably?) "fail" very suddenly in the face of new competition. So both ends of the tension between individual good / species-level good can be observed in the world, and it seems that in the case of sexual reproduction species-level good mostly dominates.
I'm not aware (disclaimer: I am an uninformed layperson) of similar conflicts between immortal species and aging ones for an ecological niche. The picture I have of the world is that certain niches are filled by immortal organisms, and other, more macroscopic niches are filled by mortal ones. Though typing this out makes me wonder about things like jellyfish.
To sum up, without seeing much evidence of strong selection for increasing lifespans, or increasing reproductive spans (the individual perspective counts!), and with the general bias not to invoke group selection where individual selection will do, the mortgaging-the-future approach to aging seems like a better explanation to me.
Ebola doesn't 'target' humans. Ebola's obvious symptoms and mortality rate in humans limit its ability to spread efficiently. The flu virus or cold virus has been far more successful in penetrating the human ecosystem. Perhaps Ebola has been selected for being stable in the bat ecosystem. The mobility of bats also makes them an excellent transmission vector, which a virus would ideally want to be non-symptomatic.
Given the massive die offs from the fungal infection that is completely devastating US bat populations, I'd say their immune systems may be unique, but they aren't miraculous. The outlook for North American bats is very grim. http://en.m.wikipedia.org/wiki/White_nose_syndrome
Birds are also long-lived, compared to mammals of similar size. One of Nick Lane's books discussed this and something about their adaptations against damage from respiration -- either Oxygen or Power, Sex, Suicide, I forget which.
Why are bats the litmus test for rabies, then? That just seems a bit odd. And why is rabies so prevalent/dangerous in bats that even breathing the air in bat caves can get you the disease?
Dangerous for humans, you mean. The fact that a species can survive while being so disease-ridden that they routinely kill the animals they infect seems to lend credence to the "super-immunity" claim.
I'm not sure this is actually the case for bats, but assuming your statement is true, it seems to be evidence for the presence of super-immunity, rather than against.
The premise sounds quite solid: The unique challenges of being a flying mammal require spending lots of energy. Which leads to lots of free radicals. Which leads to lots of DNA damage. Which increases selective pressure for DNA repair.
Evolution normally doesn't select for organisms that are able to survive aging, because, from the standpoint of natural selection, once your reproductive years are past, your survival doesn't matter.
That aging resistance would be an incidental benefit of general DNA repair mechanisms that evolved in response to a lifestyle that encourages free radical formation makes a lot of sense. The specific molecules and reactions involved in bats probably will provide important clues to the aging process in mammals, even if the adaptations in bats can't be translated directly into treatments for humans.
How immunity and disease fits into this picture is less clear from the article. But the aging angle alone is enough to make this research very interesting.