New paper claims that evolution has stopped in a bacterial species. Is it true?
whyevolutionistrue.wordpress.com
whyevolutionistrue.wordpress.com
This is (and the article agrees) a statement not compatible with modern evolutionary understanding. Primary school-level knowledge about biology should be enough to debunk this claim: a set of genes survives if there are organisms that pass those genes on, it's as simple as that.
If there is a mutation in a homogenous group of individuals, and that mutation is not lethal or otherwise causes the individual to die before procreation, that mutation survives - selection pressure or not.
There are also genomes that remain highly preserved over long stretches of time, which should likewise not be surprising. This occurs even at the gene level: there are genes in all of us pretty much unchanged compared to early eukaryotes, mostly because the proteins they produce work well, but also because mutations to those sequences are generally lethal.
While most mutations are lethal, it's not true that the remaining ones are beneficial either. This means there are lots of individuals with sometimes distinctive properties which are still causally disconnected from selection pressure.
Anyone who spent some time experimenting with evolutionary models on a computer should know this, because those are intrinsic properties of genetic systems. We expect them to behave that way. We expect ancient versions of organisms to stick around if there was no reason for them to die out. That doesn't mean the reverse is true in the sense that no change in selection pressure leads to genetic stagnation.
Evolution is an event driven process and given there is time between events, there can be a long time between events.
And if there were no possibility of time between those events, everything would look like the end of Akira.
There are several reasons why genomes remain more stable than others, including - as you stated - replication accuracy (which can nevertheless not be 100%), but also survival chances of random mutations, and environmental factors that make deviations from the plan unfit for survival.
Yet, bacteria in general show tremendous genetic mobility. They're easily the most promiscuous lifeform on the planet, considering the fact they have evolved a P2P genetic data transfer mechanism that doesn't require procreation.
So, all things being equal, the rate of genetic change is expected to vary a lot. It's also worth considering that just because ancient versions are still around, that might still mean there are diverse offspring which are also doing fine. It's not automatically the case that earlier versions get replaced.
> I'd be willing to bet that there is a healthy species of bacteria that has stopped evolving
It sounds weird, but that's mostly a matter of definitions. If a species has stopped evolving, let's say because it developed a 100% accurate replication mechanism, that species will have trouble surviving changing environments. Sooner or later there will be a virus or something else that just wipes it out.
There are several flaws in your argument: 1) There is no known polymerase that has a fidelity of 100%. There will always be some number of replication errors when DNA is synthesized. 2) There are lots of mutagens in the environment. UV light, mutagenic chemicals, hell, even radioactive decay of mostly-stable elements will occasionally hit a base and cause a mutation.
So, no, there is certainly no species that meets your criteria for non-evolving.
Second, sexually reproducing organisms, theoretically, will decrease their mutation rate over time until eventually they no longer mutate at all. And so no longer evolve.
Most (non-neutral) mutations are harmful. So any gene that decreases mutations (e.g. better DNA copying or repair) will have fewer unfit, mutant children. These children will than propagate the gene more. Even if a gene that causes higher mutations eventually creates beneficial mutations, they will just mix into the general population after a few generations, and not provide a fitness advantage.
2. "Most mutations are harmful" -> this is patently false. A lot of mutations are inconsequential, some are harmful, some are beneficial.
3. "sexually reproducing organisms, theoretically, will decrease their mutation rate over time" -> this isn't true. Mutation rate is variable over species and over time.
4. DNA duplication is a complex biological process with many moving parts. There isn't such a straightforward thing as a "gene that decreases mutation".
Changing environments can help organisms break out of local optima, but that doesn't imply they don't exist. There are countless examples of organisms getting stuck in local optima. E.g. horseshoe crabs haven't changed in hundreds of millions of years.
Most traits in general are stuck in local optima. Theoretically large changes could improve them, but it's unlikely to happen by random chance.
>"Most mutations are harmful" -> this is patently false. A lot of mutations are inconsequential, some are harmful, some are beneficial.
Who are you quoting? I never said that. I said most non-neutral mutations are harmful. Neutral mutations don't do anything and so don't matter.
>Mutation rate is variable over species and over time.
>DNA duplication is a complex biological process with many moving parts. There isn't such a straightforward thing as a "gene that decreases mutation"
There are many mechanisms that control mutations, like DNA repair and copying mechanisms, or shielding from radiation and mutagens, etc. Of course it's probably very difficult to reach perfection, which is why organisms still evolve. I just said theoretically, evolution is always pushing towards less evolution.
No. They may have barely changed in morphology, but that doesn't mean they are "stuck in local optima". And even then, it seems they have changed morphologically in some ways. https://whyevolutionistrue.wordpress.com/2012/09/14/horsesho...
> I said most non-neutral mutations are harmful.
That is just false, and I don't know how you came to that idea.
> Neutral mutations don't do anything and so don't matter.
Again, false. Mutations can have no impact on a population until that mutation interacts with another mutation (e.g. because the population bred with another population that has other mutations), resulting in a net evolutionary advantage for the species over time.
> Of course it's probably very difficult to reach perfection, which is why organisms still evolve.
There isn't a notion of "reaching perfection" in evolution. That's a fundamental misunderstanding of how it works.
> I just said theoretically, evolution is always pushing towards less evolution.
No. There is no "theoretically"- evolution is a well observed and documented process. And if you observe and document the real world, you will notice that the evolutionary process is certainly not pushing towards "less evolution".
Please stop posting misinformed comments that may confuse or mislead readers who take them to assume you have a good understanding of the topic. If you wish to comment on the topic, please take the time to inform yourself first from scientists who work in the field, rather than from your own baseless speculation. A good start is here: http://evolution.berkeley.edu/evolibrary/misconceptions_faq....
That's exactly what that means. Their morphology is stuck in a local optima at the very least. And unless you really believe horseshoe crabs are the ultimate form of life and it's impossible for organisms to improve at all, then it is "local".
>That is just false, and I don't know how you came to that idea.
And I don't know how you disagree with it. Do you really believe that most mutations are beneficial? Really? If so, exposing yourself to radiation would be beneficial for your health. Or your childrens fitness.
This is just utterly ridiculous and defies all logic. Mutations are almost all negative.
>Again, false. Mutations can have no impact on a population until that mutation interacts with another mutation (e.g. because the population bred with another population that has other mutations), resulting in a net evolutionary advantage for the species over time.
Then, by definition, it's not a neutral mutation. It's slightly positive, or slightly negative, or really positive, or really negative, but if it has an effect at all, it's not neutral.
>There isn't a notion of "reaching perfection" in evolution. That's a fundamental misunderstanding of how it works.
Perfect as in having the best fitness possible. A global optima. Where no mutation could improve it at all.
>No. There is no "theoretically"- evolution is a well observed and documented process. And if you observe and document the real world, you will notice that the evolutionary process is certainly not pushing towards "less evolution".
I'm sorry you don't know what the word "theoretically" means. My hypothesis is "If there is a gene that decreases mutation rates in a sexually reproducing population, it should be selected for over time."
This hypothesis would be difficult but not impossible to test in the real world. If we could find a gene that decreases mutation rates and introduce it to an animal that doesn't have it, and observe them for many generations. It could also be easily tested in computer simulations.
>Please stop posting misinformed comments that may confuse or mislead readers who take them to assume you have a good understanding of the topic. If you wish to comment on the topic, please take the time to inform yourself first from scientists who work in the field, rather than from your own baseless speculation.
Please stop being pedantic and misinterpreting everything I say.