So it isn't impossible for spontaneous mutations to occur its just extremely unlikely I suppose? I would think it could happen in higher creatures if it happens in lower creatures but, I don't know enough about this stuff. This did just bring a thought to mind though. 50mSV is the limit our nuclear plant workers can absorb in one year before they can't work around radioactive stuff anymore right? What about, since my world is basically running on radiation for power, a manmade gene being introduced? Like genetically modified organisms just on a smaller scale. Humanity's first attempt to increase radiation tolerance. A gene introduced into the plant worker's so they could work for longer than a year before having to move on to something else. Something to make their bodies more resilient. Could that set up proper conditions for future mutations?
Yeah, I know. I cited it because it was really the first one to report this mechanism. The second paper, from 2006, is a response to an earlier paper trying to explain the results from the 1988 paper in traditional terms. Doesn't look like this has been resolved yet, though the observed phenomena are reproducible.
@Meteor spontaneous mutations do occur in high animals. Enzymes like DNA polymerase have a natural error rate where they just get something wrong. But the body also catches and fixes errors.
What specifically do you think has not been resolved? It's not just reproducible, the specific mechanism has been described. Advances in genetic science have taken off since PCR techniques became inexpensive and bioinformatics field developed combining computer programming with biology. It's mind boggling how fast and furious new discoveries are occurring.
The mutations would of course occur, and at a greater rate with radiation exposure. The problem is there is no means of selection and amplification of the adaptive genes. In addition, advantageous genetic changes typically involve a step-wise pattern. It wouldn't be one mutation, you'd need many and they'd need to accumulate with subsequent generations. That's why it takes tens of thousands of years for a significant evolutionary change. If it were a single genetic change and you had a very prolific male with prolific offspring spreading his genome, you could have the gene amplified in the population in hundreds of years but it would still take many generations.
I didn't see anything there that indicated the SOS pathway, which I was familiar with, could result in lac- to lac+ mutation. Although having read your article, I did a quick search and it looks like there is some evidence that it can, from 1999: http://www.sciencedirect.com/science/article/pii/S0022283699932722 Which raises an interesting question, given the 2006 article that is trying to distinguish two possible mechanisms, and argues against one as an explanation for adaptive mutation.
NOTE: Actually, reading further, the later 2006 paper does account for the SOS pathway, but says that it only accounted for about 10% of the reversions from lac- to lac+ in the studied population: There's so much going on in these papers, and researchers are often so focused on particular questions, that it would probably take a lot of research to really get to the bottom of it. It's an interesting subject, though. Maybe there is a recent survey out there somewhere that looks at all of the last decade or so of studies.
I think the real issue here is the vast extent to which radiation exposure is lethal. If everyone in the word died by getting stabbed in the heart, it's unlikely that we could evolve quickly to be immune to heart stabbing.
It doesn't surprise me that only 10% of microbes use this mechanism given how many different proteins, enzymes and catalysts there are in the microbial world. But this mechanism is still known, DNA repair is suppressed in the presence of environmental toxins and other stresses. Certainly some microbes wouldn't use this mechanism at all and rely on other means to adapt. Tuberculosis, for example, relies on very slow reproduction rates when conditions are less favorable. The bacteria only rapidly multiply when conditions are favorable. Drug resistance is a serious problem but the fact treatment involves months to years of treatment has allowed resistance to develop. With the bacteria dividing slowly, and many antibiotics work by killing dividing cells, slow mutation rates are enough for drug resistance to develop. Lots of viruses have rapidly changing surface proteins, but other viruses are quite stable. Rapid mutation rates are not the only adaptive mechanism in the microbial world.
So something else is going on with the other 90%. Here's an interesting consideration: we were always taught that mutations are more likely to be harmful than beneficial. There's just a greater likelihood of screwing something up. So does turning down error correcting just sacrifice a certain percentage of the population, or it the method of doing it more focused?
With microorganisms it doesn't matter if maladaptive mutations occur. They don't effectively reproduce. It only takes one beneficial mutation to replace the entire population with that adaptation. But when there is no threat, it's better not to waste resources on cells that won't survive. I don't know the percentage of microbes that increase and decrease mutation rates depending on stresses. It wouldn't surprise me to find there is more than one means of increasing and decreasing the rate.
Oh, yes, I would assume that the vast majority of mutations would either (1) result in death or (2) be irrelevant and die out because they provide no advantage. It's the occasional lottery-winner beneficial mutation that changes the species.
Yeah. I think you're both right. So more of the population may be sacrificed, but the overall population survives as a result of the beneficial mutations that arise
If you think about more slowly reproducing species, however, many mutations exist in the genome, and they aren't killing animals off. Once in a while you might get something detrimental like sickle cell trait that offers a benefit like resistance to malaria. But more often than not, you get a mutation like the CCR5 deletion that probably provided resistance to plague and now provides some resistance to HIV. That mutation was not harmful to the people who inherited it. Among 3 billion base pairs in the human genome, there needs to be a lot of tolerance for mutations.
True. A lot of mutations are neutral, or have effects determined by the environment (in which case they may be helpful or harmful depending on the environment, such as with the moths in the UK around the industrial revolution).
Dark sand beaches are also high in background radiation, I believe (such like those in the south of spain). Fluourescent materials used in WW2 (for glowing compasses, for example) were quite radioactive too. One thing that came to my mind while reading through the posts, is that should a massive nuclear strike happen, couldn't it somehow damage the ozone layer, leaving the earth unprotected from all sorts of solar radiation?
About evolution, when it comes to evolving a species, it can take anywhere from just a few generations to thousands of generations. It depends on what change exactly we are talking about. Bacteria can evolve quickly because they go through many generations in a very short time, so they can evolve some different traits in a matter of hours or a few days. Those born in the morning have grandkids at night. Or maybe it's even faster than that, I can't recall. If we look at how we evolved for the last ten thousand years, we will find that both physiologically and morphologically, the differences between then and now are subtle. It took almost twenty times that time, for humans to evolve from a furry, slightly hunched ape to a fully upright "furless" ape. Developing something like resistence to high levels of radiation might only take a few centuries (immunity might take much longer), given that it would only take the survivors to survive it long enough to reproduce and each new generation might be a little more suited to handle it. Remember also, there are people (though rare) who are fully immune to AIDS, even though it's a recent virus. By the same token some survivors of an apocalypse might already have some level of resistence or immunity to radiation. Essentially, those might reproduce, the other ones would more likely die or be rejected due to deseases. After enough generations you'd be left with those that were resistant, who'd be passing along progressively improved versions of those genes, even if their life expectancy was yet low (which might increase their reproductive cycle). Unless I'm forgetting something, I believe that's probably close to how it might go.
