Macroevolution-a hopeful monster emerges??

I recently read in NewScientist (19th August page 11) about a paper in Cell, vol 126 p477 (couldn't access the full text) about a type of cancer in dogs that is transmissable. The cancer is thought to have originated at least 250 years ago and is spread from individual to individual via sexual contact. The cancer cells from the infected dogs were sequenced and found to be derived from a common ancestor and not the dogs themselves."The cancer escaped its original body and became a parasite transmitted from dog to bitch and bitch to dog until it had colonised all over the world" Says lead researcher Robin Weiss of University College London.My question is, is this an example of macroevolution from canivourous vertebrate to unicellular parasite? Is the cancer a new species? It is reproductivley isolated and is now an entirley seperate linage to dogs. If it isn't a new species, why not, by what criteria?Edited by 12345, : spelling

Thread moved here from the Proposed New Topics forum.

I would say no: the cancer spreading vector (organism?) puts me in mind of prions. If the spreading vector can indead reproduce, it seems to me more a virus or amyloid protein expression (prions).

The cancer cell that is spread is a cell. It contains its own full genome and is capable of replication. It makes its own proteins. It replicates by binary fission and disperses to new environments (dogs). The genome of the cancer cell is evovlving (changing over time). Its behaviour is parasitic but so are many species. The "vector" was originally thought to be a cancer causing virus because this is a very unusual thing for a cancer to be able to do. But there is no "vector". The cell itself colonises the dog. The cells DNA was sequenced and found to be unrelated to the host. The host provides an environmental niche for the cancer cells to grow but the cell grows just like other cells not like viruses or prions. Maybe "grows" in an individual dog and "replicates" by infecting new individuals may be a better way of putting it?

First off, you are right. I was very suprised when a quick look online bought up this: Canine sexually transmitted cancer: A shaggy dog story | UCL News - UCL — University College London As to whether it is a new species: Catching cancer | Ars TechnicaBut, it does go on to say that the static nature of it's gene pool means that eventually it will reach an evolutionary dead end and die.Still, I would use this as a good stick to wail on creationist wanting a dog to give birth to a non dog any day. Good find.Edited by Larni, : Tightening it all up.

Larni wrote:

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But, it does go on to say that the static nature of it's gene pool means that eventually it will reach an evolutionary dead end and die.

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Why? Couldn't it get a mutation here or there, and the deleterious mutations cause those cells to die, and the advantageous ones cause it to do better?This is reminds me of HeLa cells, a similar case where vertebrate (in this case human) cells have gone rampant:HeLa - Wikipedia

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I don't think the fate of the cell line is certain. Maybe it will muddle through somehow maybe it won't. Does this effect it's status as a species? The Dodo turned out to be an evolutionary dead end but we still call it a species. Does a "species" have to survive a certain length of time before we call it a species. Are only transitional species true species?I also thought of HeLa and the hundreds of other cell lines derived from various mammals. I didn't put these in the first post because they only survive in an artificial system but if you accept the dog cancer example it becomes hard not to accept these as well.

Do we know that this was originally a cancer? Or was it originally a {bacterial\viral} infection that behaved like cancer?ie - are ALL the DNA originally "dog" or other?Just a thought.

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Seems to me it is all dog. The only genetic change seems to be attributed to drift so they peg it as coing from a dog, between 250 and 1000 yrs ago.Somehow it adapted in such a way as to subvert the host immune sysytem too.

I'm not so sure viruses can be ruled out:

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No equivalent form of contagious cancer exists in humans. While some human cancers may be considered ”catchable’ as they are initiated by viruses transmitted between people (such as cervical cancer which is caused by certain types of papilloma virus), in CTVT, no virus is involved.

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This just means that there is no current virus associated with it as is the case with cervical cancer. It could have evolved in much the way that the HeLa cells have evolved into a self propogating cell line in spite of having human and papillomavirus as "parents".Not that there needs to be a base causal vector: all that is needed logically is that (a) a cancerous cell is transmitted from organism {A} to organism {B} and (b) the cell can survive in the new {organism\host} and propogate:

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“Secondly, recent research in Australia has revealed the existence of a newly emerged tumour in Tasmanian Devils that also appears to be caused by transmissible cancer cells, in this case by biting. Devils are an endangered marsupial species and there are fears that the new tumour might finally kill them off altogether. The methods used at UCL for dogs could help to determine whether the Devil tumour is also a 'parasitic' cancer.

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So as long as it can circumvent the immune system it should be able to survive.Interesting.Edited by RAZD, : minor wording

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Hi RAZD,I think the key element in the CTVT question posed by the OP is whether or not this "critter" represents a solid case of macroevolution. If we use the creationist definition (might as well - they're the only ones doubting that large scale evolution occurs/has occurred), to wit: "major transition between distinct 'kinds' of organisms" (eg, "lizard from a chicken egg"), then I think we can make a case that CTVT fits the bill. Consider: if Murgia et al, 2006 are correct in their hypothesis, then what we have is a somatic cancer that has evolved into a cellular parasite. We're way beyond prions or even virii here. We have actual cells that replicate, contain their own unique DNA and mtDNA, have evolved ways to mask their MHC, and operate in many ways like a "good" parasite - not usually killing their hosts, for instance. Sounds like a new "kind" to me.

I agree, but this is also why I'm a little reluctant to say the evidence shows no other element was active in the process: is the case that solid? Not what it is but how it got there is the question.It's a fascinating beastie, and the possibility that there may be more is a little disconcerting. At least they don't appear to be lethal the way many other cancers are - perhaps any versions that were lethal were eliminated by natural selection eh?Thanks.

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