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Prions Evolve Despite Having No DNA
An anonymous reader writes "Scientists from the Scripps Research Institute have shown for the first time that 'lifeless' organic substances with no genetic material — prions similar to those believed responsible for Mad Cow disease and similar, rare conditions in humans — are capable of evolving just like higher forms of life. The discovery could reshape the definition of life and have revolutionary impacts on how certain diseases are treated."
Even from a purely materialist perspective, it seems reasonable to ponder a class of materials that replicate themselves. How exactly they do so might be more or less complex but the basic idea that it's possible to configure matter in a way that it replicates itself doesn't seem that absurd. And there's no particular reason it has to be DNA --- there are even purely mechanical possibilities.
10 PRINT CHR$(205.5+RND(1)); : GOTO 10
Not really related, but it is entirely possible for humans to be "alive" in a physical sense even after they are brain dead. As long as they are hooked up to respirators etc., they can be kept alive indefinitely. To date, no human being is ever known to have regained consciousness after brain death.
The _big_ catch here is that most physicians are not properly trained to test for brain death. Most physicians will just see a flat line on an EKG and declare the patient brain dead. I used to work at an organ transplant center, where there were technicians that went through a formal checklist to make sure the patient really is brain dead. It was not uncommon to find patients who did not meet the strict criteria. In the most dramatic example, a 3-yo boy was supposedly brain dead, and he was in the operating room, ready to have his organs removed. The technicians discovered that his pupils did respond to light, so they rushed him out of the OR. On the way back to his room, the boy opened his eyes and smiled. But then he went back into a coma and died 5 days later.
Needless to say, the boy's parents were furious.
Interesting thought on that. I remember an old episode of _Sliders_ where they ended up on a world in the midst of a big fire, and accidentally brought some living (and intelligent) fire with them to the next universe. I got into a discussion (funny, I can't remember who it was with anymore) about what things would be necessary to actually have living fire. In other words, what additional things would fire need to have to be considered living and how could it be achieved in nature. We covered a lot of ground, and the conclusion we sort of got to is that, in a sense, we, and all other aerobic life at least are already a form of living fire. That's what cellular respiration is all about. It was an interesting discussion and, in the end, a lot of it depends on points of view. That of course is the problem. You don't think fire is alive because you know that fire isn't alive and if someone comes along and tells you that fire is now included in the scientific definition of things that are alive, you'll disagree, just like lots of people are still pretty upset that Pluto isn't a planet anymore. If you examine what is and isn't alive in enough detail, the boundary gets fuzzy enough that it becomes harder to know where to draw the line rather than easier.
I agree - it is important to get away from the concept of evolution as being life-based, and recognise that evolution is an emergent property of a system.
For the prion example, the key is to remember that incorrectly folded proteins accumulate and cause the prion disease - the proteins themselves are not the disease, but the accumulation is. If one folding configuration is more likely to cause other proteins to fold incorrectly, then it is natural to assume that this configuration will become eventually dominant, until a more effective configuration arises. Also, the accumulation of protein causes a feedback loop, increasing the likelihood of further malign folding. Presumably, the folding is sometimes imperfect, so this is the source of the all important mutations causing variety. Without the accumulation, I would presume that the configuration of folding has a benign effect.
So, folding configurations that increase the rate of malign folds or increase the rate of accumulation would be more successful in this feedback loop. Does this really justify the tag 'evolutionary'? It just seems that the natural progression of the disease causes what appears to be a natural selection process, but it's not clear at what point we should distinguish between a feedback loop and an evolutionary process, if indeed they are actually one and the same thing...
Putting the perils of terming new knowledge "obvious" aside, it does seem obvious that evolutionary mechanisms would have to be preexisting for life to have indeed evolved. Since the most generic definitions of life I've seen boil down to providing some form of localized reverse entropy, evolution of the materials of that reverse entropy should be able to happen before the condition itself is actually achieved.
To draw an utterly meaningless comparison, you can certainly have a power supply without a computer, but good luck doing any computing without the power supply. If that makes sense. I should probably cut my breakfast rum down to under 5 shots.
People over think evolution way to much. Sure, there are a lot of things going on, but simply put: If you suck at your job, you die. If your good at your job, you make babies. That is evolution in a nutshell. There is a slight deviation in every copy of this protein, and the ones that are better at their job reproduce. Ones that arn't so great at it, have trouble reproducing, or just die off.
Why *wouldn't* it be likely?
Darwin of course knew nothing of DNA, and his theory of evolution says nothing about it. Darwin didn't put it this way, but the key requirements for an entity to evolve are:
1. The entity contains the information needed to replicate (self-description)
2. This information is subject to random changes (mutation)
3. The environment is hostile -- some but *not all* entities will be destroyed (survival)
4. Variations between individuals make them more or less likely to survive (fitness)
DNA-based life fits these restrictions, but so do entities which store their self-descriptive information in RNA, protein, or computer memory. It places no restrictions whatever on the existence of life chemistry based around other atoms than carbon.
You can make lots of chemistry arguments about why carbon is necessary, but you can't argue it on pure Darwinian grounds. As for your specific point in favor of carbon:
Carbon has lots of free valences, which allow it to act like a universal lego-block
Silicon has the same valence properties, and also forms a wide variety of complex molecules. Phosphorus and sulfur can have valences of 5 or 6 in certain situations. Now, carbon *is* special, but not in the way you've described.
You're correct. If they evolve, they HAVE genetic material; it's a bit of a tautology.
It might be noted that, before the 1950s, biologists generally argued that DNA couldn't be our "genetic material", because it's structurally too simple. The most widely suggested storage for this sort of information was proteins, because they are the most complex chemical structures in our bodies.
This hypothesis turned out to be wrong. But there's still an old hypothesis that in the early stages 4 billion years ago or so, the early "living" things on our planet were mostly based on proteins. It's hard to come up with good tests of this, though, because RNA and DNA don't fossilize well, and we have no samples of them older than 100 million years or so.
In any case, this story is really just about finding some evidence supporting the protein-based inheritance conjecture. It's apparently valid to some degree in our modern world. It might be more widepread than just prions, but we don't know.
Something that we have known, and which was summarized well by Douglas Hofstadter in "Gödel, Escher, Bach", is that our DNA doesn't actually contain a definition of the mapping of DNA to amino acids. That is done by the proteins that "transcribe" RNA strings into the amino-acid strings for the proteins. It would be possible, by doing a bit of swapping around of the active parts of those RNA-reading proteins, to use a different DNA -> amino acid mapping, and a few variants of this mapping are known in nature. The real complexity comes about from the fact that our DNA contains genes that produce the proteins that do this transcription. But without the already-existing transcription proteins in a cell, there would be no way to discover the mapping that we actually use, because the information isn't actually in the DNA. It's "distributed" between the DNA and the already-existing proteins in the cell.
Of course, such multi-factorial causation chains (with feedback) are far too complex for most of the media, even the scientific media. So we pretend that our DNA contains all the information needed to produce us. The biochemists have known for some time that this isn't really true, but they don't make a point of it, because it "would just confuse" most of the reading public.
OTOH, Hofstadter has had pretty good sales of his book. Any nerds or geeks here who haven't read it should do so. It'll teach you a lot of fun stuff about the extreme complexity of the universe we evolved in.
(Religious people who don't believe in evolution shouldn't bother. The book isn't really about evolution per se, but it'll still get you seriously upset or confused about the nature of the universe. ;-)
Those who do study history are doomed to stand helplessly by while everyone else repeats it.