Evolution: time for some change?

One example I got about Lamarck vs Darwin was on girraffes.......

Lamarck: "In the past, all giraffes were short-necked. When food on the ground went scarce, they ate leaves on trees. When trees got taller or put their leaves higher, giraffes grew their necks so that they still could eat."
Anti-Lamarck: "Look, dinos extinct....."

Darwin: "There were a lot of giraffe specieses on earth, but primarily, there were those with long necks and those with short necks. As food was starting to grow at taller places, short-necked giraffes died from starvation, and the long-necked kept living."
Anti-Darwin: "Hello...... we can relate nowadays bird with achaeoptheryx......"

 

Log in or Sign up to hide all adverts.

Yes, but the reason that I brought up the speciation example is that Lamarck's theory doesn't very well explain why two populations, when they evolve different characteristics, sometimes speciate - that is, can no longer interbreed.

If I understand Lamarck correctly, interbreeding between any two animals should only be prevented by mechanical problems (too big vs. too small), because there isn't any pressure for the reproductive systems of the two populations to change.

 

Log in or Sign up to hide all adverts.

evolution is the change in gene frequency over time:

that seems a bit a daunting prospect for elucidating the problem of the evolution of viruses.

An expert was telling me that they had 50 genomes sequenced of a certain virus type, but it was expected that there would be at least something like 10*30 ( to the power of 30). He wasn't very hopeful that they would ever be able to sequence the lot, or even a significant part of them.

 

Log in or Sign up to hide all adverts.

Why would you need to sequence them all - because they coninfect and work together?

Otherwise, unless there is another type of envrionmental effect, what's wrong with just sampling them?

I'm not sure what you mean by type, but one doesn't need to sequence each and every unique genome of a species, genus, what have you to get a reasonable estimate of the change in gene frequency (or any other DNA based metric).

Of course you'd be more likely to might miss out on pairwise correlations in changes, but you have to start somewhere.

 

he seemed to think so. He is appraoching the problem from the other side. Extremely conserved structures.

anyhoo...the problem with the DNA phages was that they were all mosaics. You couldn't make a tree anymore because of this. It is a world wide web of phages. they can all exchange and often seem totally unrelated until you happen to see an intermediate. But there are too many phage genomes to sequence as I said earlier. 10*30 is quite a big number. That is a conservative estimate btw.

 

Although I would agree that to get an accurate measure of a small rate, or to sample rare events, one would need to sequence many examples.

Alternatively one could look at highly diverged species and make guesses about what changes are most likely and come up with a stringent PCR based approach (presumably the genomes are combinations of a much smaller number of mutations if the structures are quite highly conserved).

However it sounds like he's not doing the best job picking a research topic.

 

i guess that is why they made him a professor.

 

Virus evolution

this is a nice little article by him:

The polyphyletic aspect of the story is quite nice and could be considered 'revolutionary' if you are a bit conservatively minded.

 

Perhaps it would be best to examine viral genomes in a very isolated organism which doesn't tend to come into contact with others very often... shame that it's so hard to get to those deep-sea vent creatures.

A virus that infects a monocultural organism, like a high-altitude plant or an archaebacterium, might provide the least complex set of data.

 

Unfortunately my school doesn't have an online subscription to Res Microbiol.

Also for some reason after your post "i guess that is why they made him a professor." my web browser (mozilla on linux) won't display the sciforums website. It still loads on other machines in the lab though. So I might not have much to say for a bit though not due to a lack of interest.

(EDIT - it was a stupid XFree86 update, I just had to reboot)

 

apparently it doesn't really matter where you collect these kind of viruses

 

After reading the Bamford paper I must say, I'm not sure if his main conclusion is reasonable. Granted he did point out that he was aiming to be "unorthodox and, perhaps, provocative", but I guess what he provoked in me was some disbelief.

His main point about polyphyletic origins of virsuses, is based largely on the fact that structurally homologous viruses infect all domains of life. Viruses evolve very fast - as he himself points out in very the necessity to look at structure to see the lineal relation. Why then is it not more likely that viral lineages split before Bacteria, Archea, and Eukarya than there were multiple events that lead to completely unrelated viruses?

I've never studied virology, so maybe the point that viruses may have existed before the split of the main domains of life into the three groups is not a well recognized issue. If so, I find that strange because it would have been a basic assumption of mine.

Anyways, viruses are very interesting evolutionarily for many reasons - coevolution with hosts (or hosts immune responses even), they evolve on timescales that allow one to actually follow the evolutionary process, they have very compact and finely tuned developmental programs, and their whole genome can be manipulated to form alternative points for starting evolutionary experiments.

While I find some features of the paper interesting they do not seem to be the ones he focuses on. Perhaps it is because he is being unorthodox and the field's orthodox focus has aimed at the more interesting features of viral evolution and attributes. I find it very unfortunate that most scientists are more interesting to speak to about a subject than they can discuss in papers, I'd probably find it quite interesting to speak with him in person ...

 

Genetics reflects design (which does not imply a designer, necessarily) and for me, measuring the adaptation of a creature is more important than measuring a statistical change in DNA.

 

Craig said:

However, if you believe in preadaptive changes, a series of relatively invisible genetic changes can end in a sudden (evolutionarily speaking) change; DNA changes, even those with no direct appearance, can still have a drastic effect on an organism's phenotype. Morphological changes (the apparent adaptations) are important, but determining the rate and mechanism of genetic change can help to predict/understand the morphological changes.

 

Preadaptive change is part of adapation. Create 100 beasts, each with a different way of doing task A, and then unleash them on reality. The ones that aren't killed represent an optimized methodology for task A.

 

True, but preadaptive change is not an adaptation until the situation arises where it is useful; a morphological assay of a population may miss preadaptive changes, and so the morphological approach is not a sufficient description of evolution.

 

I don't know anything much about this, and my apologies if I've misunderstood, but if what you say is true then wouldn't it mean that it is entirely a matter of luck who survives best, and also which adaptions survive best?

That is, if adaptions only becomes useful after environmental change then it would be a matter of luck which members of a species happened to have some non-useful features capable of becoming considered as advantageous 'adaptions' after the change.

That's convoluted. What I'm struggling to say is that if before the change features are not useful then surely they cannot become 'adaptions' just because, by luck, the environment changed to make them so?

Canute

 

I think the idea in preadaptive change is that certain adaptations to do task "A" better also make it more likely that you'll do task "B" better even though you've never had to do task "B" before. Therefore preadaption is to some extent the evolution of more generically favorable systems - ie robust to more environmental perturbations and the like.

I too have little familiarity with pure evolutionary science/though though and may have misunderstood or misremembered the idea.

 

If that's true then I'm going right off adaptionism. Can someone give the official line on when a 'spandrel' becomes a selected for trait?

 

I'm not sure what you are looking for....

genetic assimilation.

genetic information exists but is not selected for. The organism is place in a new environment and selection takes place for this previously 'hidden' genetic information. The phenotype changes accordingly. We place the organism back to the original environment, and the phenotype persists, despite the presence of new selective pressure.

example:

limnea. They produce elongated shells in deep water. When placed in shallow water a new phenotype appears that deals better with the new situation; shorter shells. When put back into deeper water the shells remain short.