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Mark Vincent

Thanks to all you for posting comments, and especially to Marcy and Garry Nolan for taking it seriously.

There are parts of this whole thesis about which I feel more confident, and parts that I am less sure of. It is difficult, for instance, to see what long-term advantage there is to metazoa to have their constituent cells go rogue, and destroy the metazoan body in the process; how can this trait be passed on to offspring to give them a leg up over the competition, unless the parents themselves are the competition. And as one goes a little way up the eukaryotic tree, it is increasingly unlikely that the entire metazoan itself can be re-constituted from one rogue breakaway cell. It is possible, however, that in simple metazoa this strategy might have been advantageous under conditions of stress, as an alternative to encystment, say. Perhaps just breaking away in the water and going it alone might not necessarily have entailed eating the rest of the organism, although this kind of macro-autophagy ("cancer cachexia", or microbial cannibalism) could be a survival strategy under conditions of nutritional deprivation, or other environmental stress.

There are many conditions which might signal to the cell that the whole organism was in trouble; food shortage is surely one of them; injury is another; chemical toxicity,including attack from other species; thermal stress, pH, salinity etc; every environmental parameter has its limits as to what can be tolerated and metazoan cells talk to each other constantly.

"But cancer as cellular growth with the brake lines cut...": this is not excluded by what I am saying, but cancer is so much more than that. The whole nature of the beast changes very fundamentally; it's not just normal cells piling up. They are different chromosomally,they have a very different energy economy, they cannot die properly, they skillfully exploit the host and they truly resemble microbes in so many ways (see the diagrams). Since all cancer cells end up almost the same as each other, it is much more likely that what we have is an ancient program de-repressed as a result of the cutting of the brakelines (eg by mutagens), and not a new invention every time, that just happens to end up the same.

I think the cell is a "kluge"; it has to build on top of what came before, and what came before metazoa were microbes. Protists, if you like. When the brakes are cut, this is what sits up and grunts.

I don't think we know what the long term prospects were for single cells in a primitive aquatic environment. Single cells have a number of advantages over multicellular animals: motility, for one, and another, they are more difficult to catch and eat. Furthermore, they can mutate more without threatening the integrity of the whole organism. And they can probably survive on less food, and also survive dessication by encystment easier than a larger animal.

I agree this is all difficult to prove or disprove; however, we do know it is possible to culture enormous quantities of transformed cells in aquatic environments, eg hybridomas, to commercially make antibodies, so I don't see anything inherently impossible about it.

Thanks again to all


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