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The reverse happens as well. Consider DNA repair. Evolution requires a certain level of mutation in order to work. If a species evolves perfect DNA repair mecha

The reverse happens as well. Consider DNA repair. Evolution requires a certain level of mutation in order to work. If a species evolves perfect DNA repair mechanisms, then it will stop evolving and eventually go extinct. However on an individual level, DNA repair is highly selected for. Any individual with lower mutation rates is much less likely to die of cancer. Much less likely to have offspring with harmful genetic disorders. After all, the vast majority of mutations are either neutral or harmful, not beneficial. So individuals with the repair gene will tend to have more successful offspring than organisms without, and the frequency of the gene will increase. Most genes that could improve evolution itself are not selected for. Individual fitness matters, not group fitness. There are other ways evolution hurts itself. For instance there is a condition in mice that lives on the male chromosome. It causes all of it's offspring to be male. So all of them also carry this condition. Thus the condition spreads itself twice as much as the competing genes. And so it quickly fixes itself in the population and then there are no more females.

blacksmith_tb 10y ago
D. radiodurans has evolved something close to 'perfect DNA repair mechanisms' without becoming extinct [1] I would say the heightened risk of extinction relies on the assumption that the environment will change and the organism will not be able to adapt (without mutations). But for many bacteria, that seems unlikely to occur. 1: https://en.wikipedia.org/wiki/Deinococcus_radiodurans#Ionizing-radiation_resistance https://en.wikipedia.org/wiki/Deinococcus_radiodurans#Ionizi...
- Houshalter 10y ago
  That is very interesting. Although there are more sources of mutation than just radiation.
- webmaven 10y ago
  We've observed in the lab that in bacteria harmful changes in the environment increase the number of mutations. Further, we've observed that in many cases the mutations tend to be in the genes that are most closely related to the change. That is, if the PH drops to the point it is causing mutations, many bacteria will tend to get those mutations in genes that are likely to increase tolerance for acidity! Now that is what I call evolved evolvability.
gliese1337 10y ago
> For instance there is a condition in mice that lives on the male chromosome. It causes all of it's offspring to be male. So all of them also carry this condition. Thus the condition spreads itself twice as much as the competing genes. And so it quickly fixes itself in the population and then there are no more females. Only if the offspring of regular males can't compete well enough to keep producing females! I don't recall the name offhand, but there is a species complex of fish that live stably in a similar situation- effectively, there is one species that consists of normal males and females, and another species that consists solely of males which parasitizes the other's females for reproduction, and thus steals genes from the "normal" species.
AbrahamParangi 10y ago
> For instance there is a condition in mice that lives on the male chromosome. It causes all of it's offspring to be male. So all of them also carry this condition. Thus the condition spreads itself twice as much as the competing genes. And so it quickly fixes itself in the population and then there are no more females. It is not at all guaranteed that this condition would lead to the extinction of a population unless that population was of trivial size (and therefore unstable). Consider that as the fraction of males in a population goes to 1, the reproductive success of males goes to 0 and the reproductive success of females goes to 1. Therefore we should expect that there will be an extremely strong selective pressure on producing female offspring in greater and greater proportion.
- 3pt14159 10y ago
  Only on the first order. Say population is 90% conditioned male (ie, only male children), 5% normal male, and 5% normal female. Only 1 in 19 males mate, while 100% of females mate. Only those females that mated with normal males produce female children. Which means that barring some sort of mutation or drift, the population will eventually go extinct. One possible solution is that a normal male may have a distinctive feature that a percent of females find attractive which could be selected for.
  - AstralStorm 10y ago
    Another solution is that the broken males will engage in some sort of discernible behaviour. Yet another is that smaller populations with this issue will survive in places that couldn't be reached by the damaged one and will repopulate.
- Houshalter 10y ago
  But the males without the gene are indistinguishable from those with it. They reproduce at exactly the same rate - there is no selection pressure for normal males. You can try it in computer simulations if you like. It would be trivial to set up. Each generation the percent of normal males decreases. Eventually they are all gone.

blacksmith_tb 10y ago

D. radiodurans has evolved something close to 'perfect DNA repair mechanisms' without becoming extinct [1] I would say the heightened risk of extinction relies on the assumption that the environment will change and the organism will not be able to adapt (without mutations). But for many bacteria, that seems unlikely to occur. 1: https://en.wikipedia.org/wiki/Deinococcus_radiodurans#Ionizing-radiation_resistance https://en.wikipedia.org/wiki/Deinococcus_radiodurans#Ionizi...

Houshalter 10y ago
That is very interesting. Although there are more sources of mutation than just radiation.
webmaven 10y ago
We've observed in the lab that in bacteria harmful changes in the environment increase the number of mutations. Further, we've observed that in many cases the mutations tend to be in the genes that are most closely related to the change. That is, if the PH drops to the point it is causing mutations, many bacteria will tend to get those mutations in genes that are likely to increase tolerance for acidity! Now that is what I call evolved evolvability.

gliese1337 10y ago

> For instance there is a condition in mice that lives on the male chromosome. It causes all of it's offspring to be male. So all of them also carry this condition. Thus the condition spreads itself twice as much as the competing genes. And so it quickly fixes itself in the population and then there are no more females. Only if the offspring of regular males can't compete well enough to keep producing females! I don't recall the name offhand, but there is a species complex of fish that live stably in a similar situation- effectively, there is one species that consists of normal males and females, and another species that consists solely of males which parasitizes the other's females for reproduction, and thus steals genes from the "normal" species.

AbrahamParangi 10y ago

> For instance there is a condition in mice that lives on the male chromosome. It causes all of it's offspring to be male. So all of them also carry this condition. Thus the condition spreads itself twice as much as the competing genes. And so it quickly fixes itself in the population and then there are no more females. It is not at all guaranteed that this condition would lead to the extinction of a population unless that population was of trivial size (and therefore unstable). Consider that as the fraction of males in a population goes to 1, the reproductive success of males goes to 0 and the reproductive success of females goes to 1. Therefore we should expect that there will be an extremely strong selective pressure on producing female offspring in greater and greater proportion.

3pt14159 10y ago
Only on the first order. Say population is 90% conditioned male (ie, only male children), 5% normal male, and 5% normal female. Only 1 in 19 males mate, while 100% of females mate. Only those females that mated with normal males produce female children. Which means that barring some sort of mutation or drift, the population will eventually go extinct. One possible solution is that a normal male may have a distinctive feature that a percent of females find attractive which could be selected for.
- AstralStorm 10y ago
  Another solution is that the broken males will engage in some sort of discernible behaviour. Yet another is that smaller populations with this issue will survive in places that couldn't be reached by the damaged one and will repopulate.
Houshalter 10y ago
But the males without the gene are indistinguishable from those with it. They reproduce at exactly the same rate - there is no selection pressure for normal males. You can try it in computer simulations if you like. It would be trivial to set up. Each generation the percent of normal males decreases. Eventually they are all gone.