As I just got my exam results back to find that I didn't do nearly as well in 'Infection and Immunity' as I should have done - I'll leave you in Craig's capable hands.
Craig Anderson (firstname.lastname@example.org) writes:
I read a speculation on the flood that mentioned viruses not being able to infect bacteria. I'm a medical student at Boston University with a decent background in epidemiology and evolution and I'll just throw out some of my own speculations on the game combined with some science. Viruses can, in fact, invade any host cell. Viruses work by injecting their own DNA or RNA into a host cell (different viruses infect bacteria, plants, animals) which then enter in to a certain cycle. Cells express the genes in their DNA by the process of transcription and translation which I'm sure anyone who's taken biology is somewhat familiar with. RNA viruses take over the cellular machinery that assembles amino acids into proteins, thus they simply make more and more viruses until the cell explodes releasing those parasites to infect other cells.
DNA viruses actually integrate themselves into the host's genetic code, allowing them to stay dormant for a while, then entering into the lytic cycle described above at an unspecified time. As I've read in your site, 343 guilty spark describes the flood as 'spores' which are released when rangers tap into the spinal cord. Spores are not viral, they're bacterial. Spores are super-resistant hard shells that carry genetic material until environmental conditions are correct where they transform back into bacteria. Anthrax is an example of a spore-forming bacteria. My impression of how the Flood 'disease' works is that:
1. Spores obviously start out being carried by rangers (which are either some higher level multicellular version of this same bacteria, or perhaps a genetically engineered spore carrier, or even a symbiotic host)
2. the rangers then insert themselves into the spinal cord or whatever main nerve axon runs through the host species
3. The spores are released into the central nervous system where the hard spore (thermally sensing that it is safely within the host) transforms into the active bacteria
4. bacteria generally release toxins as their main weapon. The flood's toxin must need a very highly evolved nervous system to operate (in other words it needs a highly cognitive, sentient host)
5. The brain, which is rich with millions of neural connections in intelligent beings, is then attacked by the bacteria and its toxins. Perhaps the way it takes over the host's functions (like muscle movements and even memory) is by forming its own neural connections with the nerve cells already present in the host's brain. Preprogrammed electrical signals (action potentials) may fire into the host's brain from the flood bacterial cells, thus causing the observed behavior from flood infected species. Thus the bacteria itself is similar to a neural cell in that it can form connections with other neurons and send information (in the form of action potentials) and force them to behave a certain way. Not only that, but there are also all the obvious physical mutations inherent with the infection. So, using relatively simple biological functions, the disease could effectively take over the host's entire body and mind and incite it towards extreme homicidal behavior.
6. Perhaps the bacteria also stimulates the manufacture and release of certain 'flood' hormones (which become airborne) that keep large groups of hosts together and on the same wavelength. This could account for how flood-infected species seem to act as one coherent unit the whole telepathy thing doesn't really fly with me, unless it's that crazy gravemind thing that seems to have an immense amount of cognitive ability.
The 'infected trees' may demonstrate how life forms without nerve impulses are only infected very superficially. The higher the level of sentience, the more effective the disease is at its function.
So I'm gonna keep rambling here and speculate a little more. I don't think that this 'forerunner' would just stumble upon, capture, and decide to study these things.. they don't seem like naturally evolving species; no evolutionary system could sustain something like this. Plus, if you just randomly discovered something like this, your first thought wouldn't be to build giant ecosystem-imitating rings capable of destroying all sentient life just to STUDY these blammers. I think the forerunner were definitely trying to biologically engineer these things. There must have been some enemy which the Flood was meant to destroy; or perhaps even warring factions within the forerunner spurred on the development of the flood as a weapon. The halo's are perfect testing arenas for biological warfare. They can imitate any climate, probably even those vastly different from earth-like planets, to see how this bio-weapon will perform. I think some forerunner military and scientific minds got together on these facilities to prepare to fight something or someone.
As for the main weapon of Halo and its purpose, function, and use, I'll have to contemplate more. But it seems to me that its first use didn't just destroy all life in the galaxy. 101,217 years is not enough time for new life to spring up on more than one planet. The amount of time it takes life to evolve from single celled organisms to more complex forms like plants and animals takes time in the billions of yearsힿ there's gotta be some other explanation, and I don't buy that there's a type of energy burst that can pick out sentient beings and kill just them and not other life. Maybe the main weapon of Halo is actually some kind of Flood dispersal weapon If they can teleport things back and forth across the Halo, maybe they can use a super powerful energy burst to teleport flood carriers to the far reaching parts of the galaxy.. This would effectively kill off any sentient life on planets, moons, and perhaps the teleporting burst could even transfer the flood to starships. Then there is the ark which I would suppose is somehow resistant to the energy burst released by the halo because of its own energy field or the material it is made out of it must have contained the few remaining forerunners, or slave species, or something to carry on anyway. Maybe the Halo is fortress world because it is the place from which the forerunner made their final stand against something, using the main weapon to disperse their biologically engineered flood super weapon in a last ditch attempt at survival.