The two major schools of thought on the origin of zombies are:

1) Zombies evolved from humans much as humans did from apes.

2) Zombies are borne of a natural or man-made virus.

Though evolution would explain how zombies sporadically appear in Romero Zombie movies this can be ruled out because a majority of zombies cases were reported during the 1900's which would mean that their evolution happened practically overnight.

Plus, the evolution from thinking humans into zombies which continue their survival via bites/exchange of bodily fluids would require extreme changes in human physiology. One of those changes is a switch from sex to biting non-zombies for reproduction. Sex is one of the basic instincts of a human!

This is however, not impossible if for some reason this increases survivability. This is an extremely unlikely scenario however.

This leaves natural and man-made viruses; a natural virus would be unlikely because as stated earlier, most outbreaks were in the 20th century and we would have found it in the wild by now. If it hasn't appeared now, there's little to suggest it will do in the 21st century.

This leaves the man-made virus which would make sense because most infection occurred when medicine as a science was formed (IE, 1900's). The virus could be accidentally created while experimenting on test subjects like monkeys or the virus could be made intentionally for some unknown reason.

As an example, a couple of the likelier scenarios is the virus getting created through neurotoxin experiments and genetically selective weapons (termed "ethnic bioweapon/biogenetic weapon" in Wikipedia). These kinds of experiments are likelier to create the virus inadvertently because:

1) Neurotoxins affect the nervous system, and are capable of altering brain processes. Pretty much everyone agrees that this is what ultimately separates a zombie from a human.

2) Biogenetic weapons use viruses that target only people with specific genes. This advanced field of research is more likely to be capable of creating a z-day virus.

First off let it be known that zombies are not dead, it just seems like that because the victim shuts down into what seems to be a coma-like state while the brain is being infected (explained later). Because the zombie is still alive, there would be no reason for it to move slowly. On the other hand though the zombie could not run faster than their former self, albeit they will be able to run longer because the brain will not be operating like it would on a human and thusly the zombie would not feel fatigue. This does not mean that the zombie will be able to run forever because eventually a combination of lactic acid and ATG usage would make it collapse.

This article is far from finished but I'm taking a break, it should be finished by Halloween though, feel free to comment in the mean time.

I can simply tell you now. Zombies have a better sense of smell and hearing they just have terrible eye sight [debated]. However, as said earlier, a zombie cannot have much greater capabilities than its former self. Having a much better sense of smell and hearing would require complex physiological changes to take place.

So if your going to travel do it in the day so you can see them remember there eye sight sucks due to retinal and tissue damage. Other then that carry a crow bar or hatchet on you at times and have fun with the free for all no consequence murder fest [debated, if so, surely survival is a walk in the park?].

Real SkinZombies; Jobs; Considerations And Issues.
However unlikely, a condition similar to a skin jobzombie outbreak is NOT totally implausible; Indeed, with terrorists trying to develop such delightful toys as biological and nuclear/radioactive weaps, and considering that these people ARE quite innovative (they are not stupid; over half of al Qaeda’s top 10% staff, equivalent to the Commandants of the Marine Corps and Coast Guard and Secretaries of the Army, Air Force, and Navy and their immediate staff, have doctorates in various fields; many lower level leaders have various degrees, to roughly 50% of the overall organization), we should turn a wary eye to what ‘could’ be.
And it’s a good way to scare your co-workers into thinking you’re REALLY off kilter.