A zombie is purportedly a dead person whose body has been re-animated... [Other] more macabre versions of zombies have become a staple of modern horror fiction, where they are brought back from the dead by supernatural or scientific means, and eat the flesh of the living.
The notion of zombies has been pretty here-and-there for me as a writer. On one hand, it's a powerful tool that can denote a substantial atmosphere of dread when used properly; On the other hand, it's become a generally overused element that doesn't immediately scare audiences as much as give them the impression of an uncreative concept. Much like the zombies themselves, they can either help or seriously hurt one's professional reputation.
I won't go into a detailed history and analysis of zombies here. To be honest, I located an astounding number of established references while surfing the web this morning -- some satirical, some questionable -- and I'm certain that a little bit of legwork should answer all the background questions you have about the undead phenomenon. At the very least, there's already a link to the Wikipedia entry up there, just underneath the title of this post.
No matter how many sites I visited, however, this morning's research failed to provide a concrete answer to the question that had been bugging me since last night: Why do zombies eat brains, anyway?
Most of the references I visited tended to agree upon a single zombie "stereotype" in modern media and entertainment. For one, the undead are usually re-animated corpses, or victims of a virus or condition that manifests in a similar appearance. Usually being of a non-cognitive, nerveless state, these stereotypical zombies invariably shamble around at a less-than-optimal speed. They prove resistant to environmental threats, physical pain or the dislocation of limbs. They may either be controlled by a single external intelligence, or may retain a primitive pseudo-bestial instinct per individual. They are particularly hostile to the presence of living beings, to the point of immediately attacking and killing any perceived targets.
That, and zombies eat living flesh. There's a bit of a logical disconnect here, to be honest: I suppose that every, er, "animate" being should have to have something to eat, yes... but modern media seems to accept the background notion that zombies are just as perfectly willing to eat beef shanks or pork slices when they clearly aren't willing to feed on each other. It's more a minor contradiction, though, than anything else.
What I don't understand, though, is why we play host to the perception that zombies eat brains so easily. It doesn't even exist as a fringe understanding, mind you -- despite the fact that very few comprehensive zombie references on the Net mention the undead's tendency for brains, there seem to be plenty of incidences of the association floating around. Do a search for "eating brains" on Google, for example, and you'll find that the vast majority of your results most definitely won't be centered around Fear Factor.
I suspect that the first vestiges of the zombie-brains association came about from Dan O'Bannon's Return of the Living Dead, the first movie to reference the neural delicacy. Return of the Living Dead, however, merely explained that human brains "ease the pain" of one's undead state, and includes no specifics on exactly how or why this happens to be the case. In any event, this explanation didn't quite carry over to the media-influenced public: We can put together a mental connection between zombies and brains, but for the most part, we don't know why this connection exists. In short, we simply don't know why we could possibly think that zombies eat brains.
Wil McCarthy's "Lab Notes" column at SciFi.com actually offers an alternative explanation, albeit one that was mentioned only in passing:
Now, zombies are clearly capable of breathing, because they can groan, screech and sometimes even speak, so presumably there'd be some oxygen coursing through the system... However... zombies have no heartbeat and can survive indefinitely underwater, and... they can continue attacking even if all their blood is drained out. This implies a very robust anaerobic metabolism, probably powered by the fermentation of fat. (This would also explain the particular hunger for brains, which are 60 percent fat by volume.)
To state that zombies eat brains for their proportion in fat is still kind of debatable, though: While it does also explain why living flesh is also a distinct part of their menu (they could be after all the fat deposits, after all), it raises the possibility of other, more convenient sources of, er, nourishment. Why don't they raid supermarkets, butcher shops and liposuction clinics, then? If their senses are heightened enough to sniff out the concentrated fat in a human body, then why not do the same for presumably larger concentrations of the stuff in a single convenient place?
A flurry of responses to the same question (asked by bryanboyer) in the Ask Metafilter ("AskMe") offer up a bunch of scientific hypotheses. These range from the physiological (Brains hold both glial cells and and a high cholesterol content, which may help replicate lost brain cells and maintain cell membrane consistency, respectively) to the psychological (It's an instinctive-agressive action for the undead to regain their own lost minds) and the sociological (Because dead bodies without brains cannot exist as zombies, the practice of eating brains helps regulate zombie populations). While these proposed answers are both extremely interesting and well thought-out at the same time, they don't directly reference the current scenario we're looking at. We're looking for a reasonable explanation that not only points out why zombies eat brains, after all, but why they would hunger specifically for brains, and why they adopt a ravenous, highly aggressive stance in doing so. Perhaps the answer actually lies in some combination of these proposals.
Then again, it could simply be that zombies don't necessarily go for brains at all (despite certain media-based attempts at convincing us otherwise), and that the zombies-brains connection is just a logical fallacy that sticks to our heads without explanation. It's possible, after all, that we retain this bit of knowledge simply for its remarkability without delving too deeply into its background. In that way, it's much like any chain letter or urban legend that we encounter: We've all probably heard that one should never consume both Coca-Cola and Pop Rocks at the same time for fear of death, for example, but we never have any concrete evidence as to why this is so. We just remember a Coke-Pop Rocks connection and think little more of it.
That, and I suppose that zombies will always be zombies. They may or may not have reasons for the things they do; It's not as though we can expect them to be about as cognitive as normal human beings, after all. Otherwise they might not even be ambushing people and attempting to eat their, umm... er... brains in the first place.
With that, I'll leave this question up in the air. Even if we do manage to come up with an explanation that covers all the bases, I suppose, we'd be left with no guarantee that it'll justify the opinions of the zombie-oriented public out there. People just seem to immediately believe that zombies favor brains for some reason; At this point, I'll say that it's altogether possible that we have no such reason at all to explain the matter.