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Author | Topic: Macroevolution-a hopeful monster emerges?? | |||||||||||||||||||
12345 Inactive Junior Member |
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
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AdminAsgara Administrator (Idle past 2333 days) Posts: 2073 From: The Universe Joined: |
Thread moved here from the Proposed New Topics forum.
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Larni Member Posts: 4000 From: Liverpool Joined: |
12345 writes: My question is, is this an example of macroevolution from canivourous vertebrate to unicellular parasite? 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).
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12345 Inactive Junior Member |
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?
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Larni Member Posts: 4000 From: Liverpool Joined: |
First off, you are right. I was very suprised when a quick look online bought up this:
Canine transmissible venereal tumour (CTVT) is unique because the cells of the tumour itself are transmitted during sex. Dr Claudio Murgia, UCL Immunology & Molecular Pathology, studied tumours taken from 16 dogs in Italy, India and Kenya. He found that the DNA of the tumours was not the same as the DNA of the dogs - in other words, the tumours had come from outside the dogs’ bodies. A further analysis of 40 tumours archived in vet labs in five continents showed that the tumours were genetically almost identical and demonstrated that CTVT originally came from a single source. Canine sexually transmitted cancer: A shaggy dog story | UCL News - UCL — University College London
12345 writes: 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? As to whether it is a new species:
So, the evidence is pretty compelling that these tumor cells have left their original host, with its finite life-span, behind. In doing so, it's picked up a number of major genomic arrangements, and adapted to evade the immune system by down-regulating its MHC genes. It's clearly no longer a dog in any sense of the word, and its lifestyle now resembles any number of independent parasitic organisms. Is it a new species? Personally, I'd say yes. If so, it came about via an event that looks nothing like a speciation as we generally understand it. Catching cancer | Ars Technica 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. 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.
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Equinox Member (Idle past 5172 days) Posts: 329 From: Michigan Joined: |
Larni wrote:
quote: 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 -Equinox _ _ _ ___ _ _ _You know, it's probably already answered at An Index to Creationist Claims... (Equinox is a Naturalistic Pagan - Naturalistic Paganism Home)
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alexcj Inactive Member |
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.
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RAZD Member (Idle past 1436 days) Posts: 20714 From: the other end of the sidewalk Joined: |
The cancer escaped its original body and became a parasite ... 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. we are limited in our ability to understand by our ability to understand RebelAAmericanOZen[Deist
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Larni Member Posts: 4000 From: Liverpool Joined: |
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.
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RAZD Member (Idle past 1436 days) Posts: 20714 From: the other end of the sidewalk Joined: |
I'm not so sure viruses can be ruled out:
quote: 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:
quote: So as long as it can circumvent the immune system it should be able to survive. Interesting. Edited by RAZD, : minor wording we are limited in our ability to understand by our ability to understand RebelAAmericanOZen[Deist
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Quetzal Member (Idle past 5903 days) Posts: 3228 Joined: |
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.
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RAZD Member (Idle past 1436 days) Posts: 20714 From: the other end of the sidewalk Joined: |
... whether or not this "critter" represents a solid case of macroevolution. 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?
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. 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. we are limited in our ability to understand by our ability to understand RebelAAmericanOZen[Deist
... to learn ... to think ... to live ... to laugh ... to share.
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