Can someone input into the notion of Error Catastrophe for me.
What I am struggling to make sense of is the idea that…
Error catastrophe refers to the cumulative loss of genetic information in a lineage of organisms due to high mutation rates.
Like every organism, viruses “make mistakes” (or mutate) during replication. The resulting mutations increase biodiversity among the population
If quote 2 above were true, how then does one explain “Downs Syndrome” where an additional chromosome is found…i don’t see this being an advantage but it also doesn’t appear to me to be a loss of information either because a Chromosome is added. irrespective of either position here, it doesn’t seem to be advantageous.
Downs syndrome occurs in humans, not viruses.
Viruses don’t have chromosomes.
Neither humans nor viruses are undergoing error catastrophe.
Biodiversity doesn’t mean larger genomes or advantage.
Genome size and viability aren’t correlated.
There are at least two ‘error catastrophe’ hypotheses.
The other is the theory of ageing.
The other is a hypothesis (‘theory’) originally based on a mathematical model about the replication of viruses. It is based on an assumption that RNA viruses replicate at the edge of ‘error catastrophe’, a supposed situation where a genetic element cannot be maintained in the population as the fidelity of its replication machinery decreases beyond a threshold value. A that point, the original genetic element is supposed to practically disappear among the different variants originating from the replication errors.
A minireview about the topic concluded that the ‘error catastrophe’ hypothesis could only work in a special situation where all mutants continue to replicate, no matter what the mutation is. That is not a realistic assumption.
Minireview: Summers & Litwin 2006 Journal of Virology 80:20-26.
More generally, a large part of mutations in organisms are harmful but not all. A small proportion may be beneficial in the sense that those with the mutation have better success in some type of environments (not everywhere). In nature, the filter of natural selection filters harmful mutations away if the mutations lower the production of offspring. The rare beneficial mutations may become more common through the same mechanism.
Humans are a partial exception because of modern healthcare. It may keep the individuals with harmful mutations alive and give them a possibility to get children. That may lead to accumulation of harmful hereditary mutations.
If it helps, error catastrophe occurs when the mutation rate is so high that reproduction will always result in enough mutations that offspring are less viable than their parents.
It’s usually seen in evolutionary simulations where the mutation rates are either set too high or are non-stochastic[1]. It can occur in laboratory experiments where excessive concentrations of mutagens are used, or in areas such as Chernobyl or Fukushima where there are abnormal levels of radiation. It rarely happens in the wild.
So every organism gets the same number of mutations, rather than some organisms getting many mutations and some getting few or none. ↩︎
It is harmful if it lowers the quality of life or the prospects to get children.
The main problem is that there are no quarantee that our societies can always have fully functioning modern healthcare. In the case of a catastrophe or gradual erosion of the wellfare systems, those who are left without healthcare and medication will suffer and many die.
Depends on the viewpoint.
From the viewpoint of fitness, the children mean more than suffering. Evolution does not have emotions, suffering does not matter as long as the fitness stays high.
As humans, emotions matter and the personal viewpoint may be something different than calculating what is my fitness.
If the deleterious mutation rate is higher than the rate at which natural selection can remove them, then you get ever an ever increasing number of deleterious mutations which continually lowers fitness over time to the point that offspring are no longer viable.
For viruses, I would suspect the mutation rate has to be pretty high for this to occur given the large population size of most viruses. Some viral genomes are RNA and are copied to RNA which has a much higher rate of mutation than DNA replication, and viruses do just fine in this regime.
In my time of being a biologist the only truism I have found is that there is an exception to to almost every rule in biology. Biology is messy. What you have read about error catastrophe should not be understood excluding other possible pathways that lead to lower fitness.
Also, the word “genetic information” has been used and abused within the niche of these types of forums and the general evolution v. ID/creationism debates. In the case of error catastrophe you are talking about it would equate to the loss of functional genes through mutation.
This recalls an issue in discussion with @glipsnort where I had to concede I was in error. I found it difficult to believe a claim on a PBS program that AIDS evolved (and became immune to drugs) only because it couldn’t copy its own DNA perfectly but made mistakes. glipsnort assured me this was correct. I responded with the results of my own investigation of mutagenesis at the university library, where I found this discovery of how E-coli bypassed their own DNA repair mechanisms to preserve UV damage to their DNA. He said that is bacteria not viruses. I agreed I was wrong when I found that viruses typically mutate right on the edge of population lethality, so that one method of combating them is to increase their mutation rate.
In other words, viruses are the exception. More complex organisms have very good means of correcting damage to their DNA. But that means they can correct damage and errors selectively and mutation for them is no longer purely random. They can selectively protect portions of their DNA which are more critical to their survival, while using their own methods to introduce variation less likely to be lethal into their genome in order to make the species more adaptable. Of course, as has been observed many times, this does not eliminate all the randomness because there is no way of knowing beforehand if an error or variation is going to prove advantageous, disadvantageous, or neither. These are filtered afterwards by the process we call natural selection.
That is the only type of randomness that is claimed for mutations, random with respect to fitness. When biologists talk about mutations they often don’t include the with respect to fitness part which may add to the confusion.
Of course, Down’s syndrome is not a simple mutation, but a duplication in part or full of chromosome 21. It occurs randomly, but risk goes up with age of the parent. Those with it have decreased fertility, so seldom is passed along genetically, thus making it pretty much a non-factor in species biodiversity.
One of the important points for me in my investigation was to answer the incredulity that complex organisms could evolve by purely random alterations to their genome. Many thought that the complexity of such organisms meant the vast majority of random variations would simply kill them. I think they are basically correct and the answer is that more complex organisms don’t evolve by purely random alteration of their entire genome, they protect portions of it selectively.
Of course another part of this (as I recently pointed out) is that changes in the genome do not equal changes to parts of the organism’s anatomy as Richard often implies. It is quite a bit more subtle and complicated than that. And then there is the fact that so much of genome (so called junk DNA) doesn’t have any direct impact on the results. (But I wonder if there are sometimes longer term effects on later generations. Like maybe sometimes inactive portions get reactivated by other mutations.)
And of course by this I don’t mean consciously, but rather that they evolve mechanisms to do this because they are advantageous for the survival of the species.
Roy you have not studied this clearly…scientists have been running experiements on viruses and using bacteria for decades in an to attempt to prove evolutionary mutation is responsible for us beijg here in the first place. We came from a primordial soup right? Or dont you believe that?
How do you figure chromosomes evolved in the first place? It doesnt matter at what level we gain or lose…its still plus or minus…something that wasnt there previously or it wasnt…additional energy or not.
Doesnt the small portion of beneficial mutations fall within the statistical bell curve range where they are considered invisible to natural.selection?
Theres a study about this ive seen somewhere…ah heres the diagram
“Kimuras curve”
btw this illustration is suggested to be showing a larger scale than what is actually measured…so the problem is far worse than even this diagram by Kimura shows in that the beneficial is invisble to natural selection.
Also, what population number determines that inbreeding doesnt cause extinction? Is it 10, 100, 1000, 100,000, 1,000,0000…?
If biodiversity is such that a billion people should not become extinct, why not just 2 people?
Would you guys agree that one should be able to take just 2 people, put them into isolation and that they would re-populate without dying out or at least without suffering extreme genetic problems that put them at a huge disadvantage…which effectively means that they will lose the survival of fittest race. Do we have any examples where this has occured in history?
But why does it keep on occuring with such regularity? What im not understanding is why, if we are evolving into what seems to me to be a more advanced form of life, that these deficiencies continue unabated…one would think that dwarism, gigantism, downs …that these should dissapear…but if anything the opposite seems to be happening. I would have thought the 1-1000 for Downs would be decreasing?
I know that the stats stating Downs is not on the increase, that it remains at 1 - 1000 births, that these apparently dissagree with me despite my concern above) however i also note that Downs increases with maternal age…and it appears that we are having children later…the global trend is dedinately that we are having children at older ages…which means theres something very wrong there…one of the stats must be misleading if read in the wrong context?.
Anyway, why are most Downs born to mothers under 35? Is that simply based on total nunber of births rather than percentage of births for particular age groups? (Thats my assumption)
I dont think i beleive in the notion of error catastrophe…i dont think either YEC or Biologos view have anything to gain from that…but its early.days for my adventure into this and it does appear that even within the secular world view, there are some serious concerns about the notion it [the conspiracy if you will] might actually be true.
Im keen to explore this apparent conspiracy a bit from both persepctives here.
Reproduction is messy and pretty filled with risks. It is estimated 10-20% of all pregnancies end with miscarriage. Oftentimes they are so early the mother does not know she was pregnant, and may just notice a “funny” period. Many of the fetuses that are lost are due to chromosomal abnormalities, among other things, but Trisomy 21 happens to be one that is survivable to the fetus, so may be carried to term. Many others are not, so we really not as aware of them as Trisomy 21. Nothing works as well as you age, and the risk goes up with age, with wikipedia stating " The incidence of the syndrome increases with the age of the mother, from less than 0.1% for 20-year-old mothers to 3% for those of age 45.[4]"
Now, with the majority of births happening to younger mothers, even though the risk is smaller, the absolute numbers may well be higher. There are not a lot of 45 yo mothers, so even with a 3% risk, the total number may be small. Sort of like driving drunk makes you more likely to have a wreck, but most wrecks are not caused by drunk drivers. The other big factor in developed countries is that if you are an older mother, you will be offered genetic screening to see if the pregnancy you are carrying has Down’s. Many of those babies are then aborted, which drops the number down from the expected incidence, and in some countries, there are very few Down’s babies that go to term. But that is another subject, and the ethics of which we tend to avoid discussing on this forum, though fine to discuss the facts.
In any case, Trisomy 21 has minimal if any affect of the overall genetic makeup of the species, as it is not passed along to following generations, except in rare cases.
I hope that has been helpful, but please ask away if that did not answer your questions.
Biological genetic diversity is a component of biodiversity. Generally a population with more genetic diversity has a better chance of surviving, in contrast to one that is highly inbred. But different organisms have different tolerances.
Having the right balance of genes is important. Downs syndrome reflects the problem of having too much of all the gene products from one chromosome compared to the others. Having an extra or missing sex chromosome is the only other case of chromosome errors in humans where survival significantly beyond birth is known. However, having either a complete extra set of DNA or duplication of a smaller part can provide useful spare sequences to play around with - hybrids with extra DNA may have the advantage of more sets of immune genes, for example.
Probably most mutations have no significant effect one way or another. Small mutations have about an equal chance of increasing or decreasing the effectiveness of the gene product. (Whether increasing or decreasing its effectiveness is helpful, harmful, or indifferent depends on the situation.) Large mutations unsurprisingly tend to disrupt existing function but might move the product towards a new function.
The more harmful or helpful a mutation is, the stronger the chance that its abundance will change due to selection. But mathematically random variations in what happens to make it to the next generation mean that there is a chance of losing something useful or spreading something harmful, even without the complication that changing environments might shift what is helpful or harmful.
Although viruses have all sorts of weird options for nucleic acids compared to living things, that set of nucleic acid is often referred to as its chromosome, despite the lack of standard features of eukaryotic, or even bacterial, chromosomes.
