This is NOT supposed to start a flame war over evolution.
I’ve been discussing evolution with a friend, and he raises a point that I find interesting.
Is there an example of natural selection (the only mechanism that evolution has to modify populations, I assume) increasing genetic information, instead of maintaining it or removing pieces.
And how does this relate the “junk” DNA found in many (most?) species?
Since life started out simpler, and got more complex, that seems proof that evolution increases genetic info. Of course, if you don’t accept evolution to begin with, then them’s the breaks.
Natural selection does not add or remove genetic information - mutations do. Whether those increases or decreases in the genetic code then persist is determined by their relative value to the organism within its current environment: if the mutations are advantageous, they will likely persist; if the are detrimental, they will likely not; and if they are neither, their statistical prevalence in a population will be largely unaffected by natural selection.
And natural selection is not the only mechanism for evolutionary change. Genetic drift, for example, is another.
No actual references here, but I think there’s clinical evidence for DNA exchange between bacteria, if that’s what you mean. Also, many plants look like they got that way by not quite splitting chromosomes properly during mitosis. My genetics courses are far too forgotten for the right words to be there. But basically, you normally have chromosome pairs that pair up and split, so each daughter cell gets the same number. But in many plants, it looks like either this didn’t happen at all, doubling the number of chromosomes in the mutant offspring, or one or two chromosomes didn’t split, so one daughter has n+x and the other has n-x.
Mitochondria (the sub-cellular organelle that breaks sugar down for energy) has its own DNA, and is believed (I can’t remember if this is a controversial theory or accepted dogma…) to be derived from a separate organism that got ``eaten’’ by an ancestral cell, but not digested.
Retroviruses also add DNA to the host cell; normally this is a bad thing, but maybe once in a million it adds something useful. And hey, when you’re talking about a few billion years, once in a million is enough, right?
Ok, good point. Is there a specific example of mutations being good for the organism? Which species is the result of mutations from another species? Is this inferred from the similarity of the DNA of the two? Is there any specific method theorized for the mutations to get incorporated into the population of major parts of the species?
The entire history of life on earth is examples of mutations being advantagous. Speciation is not caused by a single mutation; if it were, similar mutations would have to occur in the same population at the same time in a male and a female, which would be ridiculously unlikely. Speciation almost always occurs when a population becomes seperated and different traits are selected for in different environments.
I don’t know if this is specific enough for you, but there have been all too many cases of bacteria or pests developing resistance to antiobiotics or pesticides.
All species are the result of mutations from other species. To be more specific, though:
Observed Instances of Speciation
Some More Observed Speciation Events
Before the discovery of DNA, the degree of relatedness of different species was inferred using anatomical differences and fossils of transitional or otherwise related forms. Certainly DNA (and also other biochemical “anatomy”, such as the forms of different proteins) is now an important part of taxonomic classification.
Well, there’s always sex. More generally, reproduction. As viking mentioned, bacteria sometimes swap genes as well, even though they reproduce asexually.
This is another in a long line of examples of why I don’t much trust the arguments from certain quarters. Thanks for the info. Thanks especially for the links to talkorigins. I didn’t know they had a standard web site.
What I’ve been told by certain people, also, is that mutations are always bad for the organism. Can someone think of a direct refutation?
Are there favorable mutations?
Talk.Origins is a really good web site for these sorts of things.
Thanks again. I just got through with a 1.5 hour conversation about this stuff, with people like Phillip Johnson being cited frequently. I’m going to study up on this.
What Darwin’s Finch said and sexual selection, selective breeding and founder effect pop into mind as possible means of adding or removing gentic information from a population.
Incidentally, Darwin’s Fich, I have lurked here a long while and just wanted to say I enjoy reading your posts. I find you usually make any point I was going to, so I don’t bother. Mind if I ask what you are a student of?
Bio-anthro here(not working in the field at the moment) of the Multiregional model of late human evolution as put together by Wolpoff and company at the University of Mich.
Ben
Sorry, need to get this preview thing down, “Darwin’s Finch”
Cite? That certainly doesn’t agree with the education I’ve had, which has taught that complexity can either increase or decrease via evolution, and it’s not trivial to predict which it will do.
Decrease in complexity: Bacteria lose introns from ancestral archaea.
Increase in complexity: We not only keep introns but have multicellularity, again starting from ancestral archaea.
Revtim means that if you go right back to the beginning, the first life was very simple. Now, we have a range of life from very simple to very complex. Compared with the original, nothing has got simpler and a lot more things have got more complex. And the average complexity has increased.
Your education is correct, but starting from a different point. If you take an organism now, you do not know whether it will evolve to be more or less complex.
Wow…thanks!
I studied “integrative biology” at UC Berkeley, with an emphasis in evolution & paleontology (with more emphasis on the latter than the former, actually, in terms of actual course content).
As something of a tangent, an article in the most recent issue of Nature Reviews Genetics (one of the publications from the Nature group) shows that the genes which result in hybrid inviability between species – the root cause of reproductive isolation – are likewise the results of natural selection.
This is a false dictonomy. Removing pieces of the genome, if done in a nonrandom fashion, is adding information.
That depends on how one defines “information”. If one considers the information content to be defined in terms of entropy, then mutations do increase the quantity of information, and natural selection decreases it. But if one defines it as being the amount of knowledge that the genome imparts, then natural selection increases it and mutations decrease it. Johnson exploits this equivocation to “prove” that evolution can’t add information; natural selction can’t increase information in the first sense, and mutations can’t increase it in the second, so by switching definitions around midargument, he makes it seem like neither can increase information.