Science vs. Zombies

Zombies.  Films more and more often are trying to legitimize horror/sci-fi concepts with scientific plausibility.  Jedi have midichlorians, and, often now, vampires have their preternatural powers conferred by virus. But zombies somehow seem more plausible yet as a sort of sophisticated version of rabies.

Not all movies give zombies the same characteristics and powers, but they tend to have a lot in common.  I'm not talking about the supernaturally undead, of course, but those becoming undead by infection with the zombie virus.  For example, zombies are immune and near-indestructible.  A bullet to the brain.  That's what it seems to take.  Stab 'em, shoot 'em, dismember 'em, and they go on.  Sometimes a body part will crawl on its own, refusing to die.  Sometimes a zombie (sometimes half a zombie) is seen wasting away to nothing, but still conscious of its surroundings in whatever way a zombie can be.

Zombie gives the Energizer Bunny a run for his money...

The problem is that there is no pathogen that can make an animal immune to toxemia.  Exposure to bacteria and other microscopic scavengers leads to sepsis, and sepsis fouls up all physiological systems.  A body still needs oxygen supplied, needs nerve-mediated coordination, needs parts of the brain for hand-eye/foot-eye coordination.  Inner ear infections will still foul the sense of balance.  A zombie is still, physiologically speaking, a cannibal, and its exposure to prions will also be its undoing.

If there were such a pathogen, it would've evolved by now.  In fact, instead of being a pathogen, why wouldn't it exist as an immunity-conferring plasmid in the organism's cells.  This pathogen seems to selectively destroy the brain matter dealing with cognition and emotion and leaves alone the parts that are needed for chasing and killing.  Not quite leave it alone.  It must keep this part of the brain alive.  Maybe even enhance the parts that deal with olfactory sense.

In spite of being largely unthinking, zombies also seem to avoid the obvious food sources available to them -- themselves -- and shuffle around starving until a hapless uninfected human being shows up on their radar.  Usually, the means of distinguishing zombies from other human beings is that they smell different.  Sometimes it is that the "living" simply do not smell decomposed.  See the above paragraphs for the obvious problem with this idea.

Perhaps instead zombies' metabolism produces proteins that give off a highly recognizable smell, a smell that masks human scent.  Rarely though, do you see a group of zombies chasing after animals.  They only show interest in the other white meat.  So the zombie virus, in some stories, would presumably confer a kind of new intelligence in its host, an awareness of human scents and an instinct to avoid eating anything else.

Much more plausible would be a disease like rabies, which causes a less discriminate response in infected animals.   More effectively contagious (and less elaborate) still would be a virus that caused its host to deliberately sneeze in other people's faces.  Or caused the host to develop various compulsive behaviors that would allow the disease to spread quickly and silently.

Assuming that nature, rather than cobbling together quick and dirty means to its ends, prefers elaborate schemes, another problem with the idea of zombies constantly seeking out fresh meat is that their attacks are too coordinated.  A swarm of zombies descends on a vulnerable human prey and gorges like lions around a gazelle.  Assuming that they don't devour so much that the victim can't come back as a zombie, the new convert to the zombie cult will probably not be in very good shape for chasing down uninfected humans.  It's a multi-level marketing scheme that very quickly runs out of steam and collapses under the weight of its short-sighted avarice.

Zombies, if not supernatural creatures, are simply organisms.  A zombie might be considered a composite organism, where the host and the pathogen together form a kind of elaborate vector for disease transmission.  But a composite organism, even if more than the sum of its parts, is still subject to all the organismal problems of energy, metabolism, waste/toxicity, homeostasis, immunity, etc.