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Evolution Can Occur Much Faster Than Previously Thought (ox.ac.uk)
An anonymous reader writes: An Oxford study on chickens discovered that evolution can make significant changes to a genome in as little as 15 years. "For a long time scientists have believed that the rate of change in the mitochondrial genome was never faster than about 2% per million years. The identification of these mutations shows that the rate of evolution in this pedigree is in fact 15 times faster." Professor Greger Larson, senior author on the study, said, "Our observations reveal that evolution is always moving quickly but we tend not to see it because we typically measure it over longer time periods."
We've never observed evolution yet
Wrong
some scientists only assume it from observed differences in the fossil record.
Not "assume", "infer", and anyway decades of molecular biology, genetics, and genomics have proven at least as useful as fossils. My favorite example here.
The paper is here but it is probably paywalled. (I have institutional access, so I'm not sure what that link will do to people who don't.)
This is part of an ongoing debate about rates of evolution. To a large extent it was kicked off by a 2005 paper by Simon Ho et al. (Ho is second author on this paper.) They observed that estimates of mutation rates derived from studies over short time periods are much higher than mutation rates derived from studies over long time periods. Short time periods are up to a few thousand years, e.g. comparing populations that have been separated by for a few thousand years, or ancient DNA compared to modern DNA in the same species, or multigenerational studies over a few years or decades such as this one. Long time periods are from comparing species whose common ancestor is typically millions of years ago.
This apparent acceleration in mutation rates is controversial.
I'm going to read the paper now, so I may have more to say later.
Quattuor res in hoc mundo sanctae sunt: libri, liberi, libertas et liberalitas.
There are two issues here. One is that a single DNA site could mutate several times. If we only see the end points, it looks like only one mutation has occurred (or even zero, if it mutates back to where it started.) This is pretty easy to correct for. E.g. if you compare two sequences and they differ in 10% of sites, it is reasonable to think that 1% of sites have actually mutated twice. (That is a little oversimplified, but not by much.)
The other issue is that a DNA mutation can spread through part of the population, but then go extinct. If you measure over short time periods, you see these mutations, but over long time periods you don't. There are mathematical reasons to think this does not affect your measured mutation rates if the mutations are neutral (neither helpful nor harmful.) Look up "neutral theory of molecular evolution" for details. However, if they mutations are slightly deleterious, this can be an issue, but there are limits to what you can achieve with this mechanism. (I wrote a paper on that once.)
Quattuor res in hoc mundo sanctae sunt: libri, liberi, libertas et liberalitas.
Let me see if I understand. By measuring over a long period, we're measuring the long term rate of mutation survival after applying selection pressure, and that could be noticeably different than the raw rate of mutation. Is that a correct summary?
Yes, that is correct. The technical term for 'mutation survival' is 'fixation'. A mutation is 'fixed' once the entire population carries it. It is 'extinct' (unsurprisingly) when it no longer exists in the population. When it exists in part of the population it is 'segregating'.
There are huge amounts of DNA that have no known purpose and appear to be junk. This is over 98% in humans, but varies a lot between organisms. The junkness of this is under debate. My feeling is that much of it really is junk, but some of it has a function we don't yet understand. (Also, sometimes the function is simply "we need a certain amount of space between these two bits of non-junk". This has a clear purpose, but is 'junk' in that the DNA letters don't matter.)
This particular experiment is about mitochondrial DNA which has very little 'junk', and that which it does have probably at minimum has something like 'need this amount of space' function.
Yes, scientists do like using 'junk' DNA for phylogeny (making family trees of organisms) because it is (we think) not subject to selection. On the other hand, you need to find the corresponding junk regions in all your critters and sequence them. It is easier to identify corresponding genes, and often someone else (who cared about the genes themselves) has done the sequencing work for you. Often the choice is doing phylogeny on genes using only a computer, when phylogeny on junk DNA requires samples and a molecular biology lab. Another issue is time scale: the junk DNA mutates faster, so it is good for closely related species (e.g. 'apes') but for distantly related species (e.g. 'vertebrates') you need highly conserved sequences (genes). The junk DNA will have mutated so much that it is all noise, no signal.
Is there a way to measure the mutation rates for different sites in the overall genome of a given organism, so that: (a) we can determine if some regions are actually junk because mutations to them do not affect organism fitness
Yes, if we have diverse organisms and a good alignment of their DNA, we can look for 'junk' regions by how much mutation occurs where. (Actually it tends to be the other way around - we see islands of conserved sequence, and deduce therefore that they have a function. This isn't how genes are detected, as there are more sensitive gene-specific ways of doing this.)
and (b) can distinguish between the rate of mutation and the rate of mutation survival?
Only I think by comparing mutation rates over pedigree time scales (a few generations) with mutation rates over long time scales - which is what this paper addresses.
Quattuor res in hoc mundo sanctae sunt: libri, liberi, libertas et liberalitas.
https://en.wikipedia.org/wiki/E._coli_long-term_evolution_experiment
E. coli evolved to eat a new chemical (citrate). It developed a new enzyme to do it. E. coli was previously defined as not being able to eat citrate. By the former definition, it has evolved into a new species.
How is antibiotic resistance a loss of function? Troll better, please.
Several of them are listed here: http://www.talkorigins.org/faq...
What I was trying to get at was that if a section of DNA performs some useful function, even if we don't know what it is, it'll tend to be preserved...
Yes.
Would such cyclic shifts meaningfully affect the assumptions underlying the multiple mutation rate?
I'd expect it to be a very minor effect. I'm not aware of anyone getting worried about this. It is a matter of statistics: if you're comparing 100,000 DNA sites, you don't care much if 50 of them behave weirdly in some fashion. If you successfully target 'junk' DNA for the comparison, it is not an issue.
A related effect is convergent evolution. Say two species of bacteria each colonize high temperature environment. Then certain mutations which are favoured in high temperature will likely occur in both of them. When we compare their DNA, this can make it look like they are more closely related than they really are. This is more of an issue in morphology (Darwin's finches, for example, or cormorants, which look very similar all around the world but turn out often not to be closely related) but it can happen at the DNA level too.
Quattuor res in hoc mundo sanctae sunt: libri, liberi, libertas et liberalitas.