How can there be so many zombies in The Walking Dead if they consume live people?

In The Walking Dead, I've noticed that often when a person is attacked by the walking dead, the victim is totally consumed. For example,

Rick's wife was eaten whole by one zombie.

So if they usually consume an entire person (or leave not much left of the original person) how can there be so many walkers? Shouldn't their numbers be smaller because they eat people whole?

Answer

The number of zombies currently has little to do with the fact the zombies consume the living whenever they get the chance.

• 
  
  

  Not knowing the source of the original event, we are never privy to how many zombies there were initially or how the infection was spread. Since everyone is infected, unless their brains are destroyed, everyone who dies will eventually become a zombie.

  
  


• 
  

  Since people don't have to be bitten for them to become zombies, nor do we know for certain how long a zombie lasts, we could be seeing zombies from the absolute beginning of the event. If they are decaying, it is at a rate far slower than the normal degradation of bodies that are "dead" so we can't estimate how many should be left after a given amount of time.

  
  


• 
  

  Accidental deaths, suicides, from the horror of it all, starvation (likely to be one of the most likely cause of new zombie creation) are all likely sources of new zombie creation. People who may be bitten but not killed (but die later, anyway) are also good candidates to end up zombies without being eaten.

  
  


• 
  

  I suspect eventually, the roaming herds of zombies will diminish as free-range humans get harder to find (either through the experience of fighting the walkers, or being exterminated by them) and their populations will slowly diminish. This means humanity will likely never truly be zombie free and will develop new ways of dealing with the dead should free-range humans get their act together against the zombie threat.