Sigh. After looking at my Ipod and seeing this play threw, I have to intervein. I actually stopped playing dark souls to get up and write this. Everything I write is do to the response and conversation of this thread. In this, I have to say, I must talk.
For one, HUMANITY is not the primary source of keeping hollow. Not the body form of hollow, but the mind form itself. The form in which the fallen undead, as we have seen, turn into mindles drones of war. The Merchants, the beings that lack humanity, are hollow in form, but not hollow in mind. Yes, the male merchant is insane in a sense, and the female merchant is there, but it is not the insanity of enhollowment, but just insanity of, well, repression, lonesome, and the sight of chaos and disparity all around them. Being as one is a scavenger merchant, and the other is a herbalist, it can be said that these hollows, although are of form, are not of mind.
The hollow, the white maiden, goes hollow in the archives. Even though she has a load of humanity that she has, since she is a 'special' breed of human that strives of it. She goes hollow after being captured by seath, for whatever experiments he has for her (likely the flawed experiments near the area). In this factor, it can not be said that Humanity keeps them from going hollow, as she clearly has a ton to hold. Some characters who are in human form, including the crestfallen and logan, have no humanity, and they have strived at being sane... until they went and did certain events, of course.
The Bonfires, as seen in Ash Lake, had derived before the second lighting. It can be said so, as the two bonfires in Ash Lake are not of the bones of humans, but the wood of the arch trees. As humans have fought against the Dragons, it can be said that they used the power of the flame to strive to survive, as the Witch of Izalith did. It is possible that the undead had existed BEFORE the second lighting, and it probably is so. The hollowment began when the second lighting was created. Now it is hard to say why that is, however it is not the lack of humanity, or at least not the primary reason why.
It is due to the 'Bizarro' flame, the Chaos Flame. With the factor of Chaos, the second cloned flame is fused with the First Flame, the Flame of Disparity (mostly, conflict and war). As well as the information of the four statues holding children, especially the one by the gate pit to the vessel's soon-to-be resting place, it could be said that the first being that was the guardian of the First Flame when it was first lit strived of humanity. As the Lord Soul of Gwyn has none, it could be another reason why. Why he has no humanity, is possibly due to the factors in which of the soldiers that are bound to the first flame, the Black Knights. As for the Chaos Flame, as it spawns the humanoid abominations of chaos, it can be said that humanity derived towards them, in which shaped and formed into such things. If you do not believe that the Chaos Flame derives of humanity, look at the Chaos Weapons and the Pyromancies of the Bizarro Flame.
Whatever the factor is, enhollowment to the mind seems to also be bound to the ideals of the Dark Sign, as seen in the eyes of the hollowed form. Perhaps this Darksign always existed, and was used as the source in which Undead Could warp to their 'home' after 'deathification', as Hollows of the flame can not die when bound to it. As it can be said that perhaps the Dark Sign is the work of the God of War, or possibly the Furtive Pygmy. We do not know why the Furtive Pygmy had vanished, nor do we see it as being ever linked to anything, other than Kaathe (which you should NOT trust so openly, I might add you). As the God of War had also vanished due to certain situations in which he was banished from his home, losing his godly deity, it can be said that he might have done something during the time when the Age of Dark began the first time, or did something to bring it about.
As for the time thing, it can be seen that Every time you use it, the bonfire, time always shifts, and everything is set back into place. The only exception to this rule, is the NPCs and the Black Knights, who do not change their actions nor what they are doing after the use of the bonfire (try it out, bring a Black Knight close to your bonfire, and try to warp it back. it won't work). It could be true that NG+ is the doing of the player going back threw time, as well as space (otherwise we would see ourselves). However, the Dark Lord ending would otherwise prove wrong, as the Dark Lord ending distinguishes the Flame (in which case, all bonfires, pyromancies, and other flamly dieties tied to it), in which would remove such times. It is a good idea, I give you that, however flawed in some cases. Just pointing it out.
The reason for the follow form is death. As you can see, it is the hollow form in which is the factor of the Flame, as it incarnates you as if reborn in a new body, however flail you are. It can be said that the reason for such things is due to what is on your heart, the scar of the firekeeper (the woman holding the toddler seems similar premise as such). With the factor in which the bonfires is distinguish, YOU, as the dark lord, would probably die without it. The reason for the hollowment to the mind, well, has already been discussed before. Mostly doing with failure.
I am not trying to destroy anyone, nor to show hatred. I am just pointing out some things. You can debate it against it, if you would like, but I shall defend it as well, unless I see proof as such in which weakens what I know, if not destroys it.