# What would be the minimum human population to sustain a single vampire indefinitely?

As per question in the title.

I recognise that there are numerous criteria that would affect this, however, I am looking for a baseline estimate that could be modified as per specific vampire (his humanity, feeding habits, discipline usage etc.) I would assume that the said vampire is drinking about 2-3 points of blood per night and never kills his victim. However, I struggle to estimate anything else than a herd size (which is composed of exclusively fit-for-purpose healthy people). Assuming that it takes about four months to recover from a loss of a point of blood without any detrimental health effects (implied by the facts that a point is about a pint, that is about a single blood donation and the medical recommendation is to donate blood at most three times a year), I propose the following calculation:

3 * 1 * 4 * 31 = 372 people required to every night feed on 3 different people, drawing 1 point of blood for four months of 31 days, so that no person is bitten twice in this period.

But that doesn't explain how many "real" people would be necessary to at all times have no less than 372 healthy specimens for an indefinite amount of time (self-sustaining population).

Could you explain how to get that number and what would be the major contributing factors?

If this question is not fit to appear here, I could possibly ask in some medical SE instead. Please comment if that's the case.

Some people ask me for purpose, let me explain. That's not supposed to be a tool to estimate the vampire population in a given city. Instead I'm thinking about a single vampire living in a remote area without a practical possibility of leaving (think Tzimisce in a settlement surrounded by werewolves in the middle of Siberian taiga). I am trying to establish how many people should such a vampire have around him to survive by purely local means. I want to take into consideration aspect like not everyone having being suitable to be fed upon, naturally occurring illnesses, necessity of children to replace the elderly etc. to create a situation where a trapped Cainite struggles to keep himself alive. There are some imminent dangers to him, hence his usage of disciplines (additional 2 points per night) but he is aware that overfeeding would steer the population to a decline. I would like that status quo to last for more than five decades. No, I don't want to factor in the social problems of people gradually noticing his presence, I'd rather think of superstitious community who treats it as a curse over a town that has no explanation and him being extra careful to influence mortals into having a lot of children and not leaving, as a local prince could in the medieval times - only in contemporary setting.

Mortals are not supposed to be willing participants, if it were like that, I'd just go with Herd Background and assume no overhead of spouses, children and elders is needed.

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Like many things, it depends. Your calculations are quite reasonable and 372 should give your vampire enough, in fact it has a decent margin of error in it. It has a decent margin of error because a healthy person can give more than 1 BP in a night. I don't have the book handy, but I'm pretty sure they can give up to 3 BP before their life is endangered. Also a healthy person can give blood more often than the medical guidelines indicate. Also, the vampire can, at least to a degree, self regulate and avoid using unnecessary blood. You will still average well above 1BP a night, but a vampire that avoids fights and is deliberately conservative about blood use can probably come in under 2-3 BP a night on average.

So, as you say 372 will provide enough, and even give some safety margin. But that is 372 adults that are at least healthy enough to "contribute" three times a year. You are asking how many would be in a community to give you those 372 healthy adults.

And that depends. You want the birth rate to be equal to or greater than the death rate, but death rates are highly variable in different time periods and different parts of the world depending on circumstances. In the United States, for instances the crude death rate is 8 per 1,000 people per year. Going with that number and ignoring the fact that that is per 1,000 in the entire population and we are only looking at health adults in our 372, he can expect to lose around 3 of his herd each year. That means to be sustainable he needs 3 that are about to become old enough waiting in the wings. If we say they are "adult enough" at 16 and we want this to be indefinite we need 3 children at each age between newborn and 15 waiting around. So, in addition to our 372 adults, we need 48 children waiting around.

Incidentally, the crude birth rate in the US is 14 per 1000 people, so for our 372 adults we could expect an average birth rate (if comparable to US) of 5, easily more than the 3 we need.

Currently, this brings us to 420 to be sustainable. But, you also won't be able to usethose with chronic infirmaties that prevent them from being used, like the very elderly. But how many elderly you have also depends. If the death rate is high, you probably won't have many. If you have customs of senicide (killing or suicide of the elders), then again you won't have many. If the vampire has a firm hold and wants to keep the population to a minimum, he might well create such a custom or else "cull" his herd of any not of use to him. If he does this ruthlessly, than 420 is enough with a decent safety margin. But, if he doesn't do this then he will have some additional people. In the US our population over 65 is 13% of total. With a base of 420 people, this makes 483 people total (13% of 483 is 63), so if this is a rough estimate of the number in his population he can't eat than we are up to 483.

I'm ignoring the temporarily sick because (unless there is an epidemic hitting a large percentage of the population) he can easily bypass them for a week and just come back. In short, they are absorbed into the safety margin.

So, I've played rather loose with a lot of the estimates and erred on the side of the vampire being cautious, but a population of 483 could sustain a vampire forever. This of course adds in the assumption that there won't be any huge deviations from average. If there is a war or plague or famine that wipes out a large portion of the population, he will have trouble.

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The question is somewhat flawed. If the question is really the first premise I list, then a minimum of 80 mortals are required for a sustainable herd population.

• A vampire wishes to have a sustained community of blood dolls, taking 2 points of blood a day
• A mortal adult has a blood pool of 10 (VtM:Rev 139, chart)
• A Kindred can drink 20% of a mortal's blood pool without causing harm (VtM: Rev 139)
• Therefor a Kindred can drink 2 points of blood from a mortal without causing harm
• A mortal refills one blood point a day. (VtM:Rev 140)
• Therefor a mortal could be fed on every other night if the kindred decided to drink 2 points of blood from one mortal a night.
• Therefor a stable herd size for a Kindred who uses two points of blood a night is 2.
• If a kindred decided to drink only one point of blood per mortal per night, they would need exactly as many mortals as blood the desire to drink every night, in this discussion, 2

Either way, a kindred would only need 2 blood dolls to sustain a diet of 2 blood points a night.

Knowing that you only need 2 mortals to sustain a vampire indefinitely, it becomes academic to determine the minimum viable population of humans. Scientists have done the work on that. The article posted in New Scientist in 2002 claims the "Magic Number" of a minimum population is 160, perhaps as few as 80 if the mortals are genetically screened for undesirable recessive traits. This provides far above the required 2 that need to live as blood dolls.

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Since you both have your own answer, rather than arguing in the comments on each other's posts, please focus on improving the case made by your respective answers on the points on which you differ. – SevenSidedDie Nov 22 '15 at 22:55

Human blood is replenished in 3 months. This is why we must wait 3 months before a next blood donation.

It would be around 1 BP / week on the rules of the VTM. But, as @Tritium21 mentioned, the actual VTM rules say 1 BP / day of replenishment.

A vampire needs 1 BP / night to survive, so a single human would it be enough for him for the pure survival. If it needs 2 BP/night, then 2 humans.

If we are thinking on really long term and somehow there is the wish for a self-replenishing herd, then:

1. First, you need to know: at least 50-100 human would be needed for a completely self-replenishing population, fewer will die out because of the inbreeding.
2. The IRL blood donation rules allows people between 18 and 60 years to donate blood. Considering their mean life aorund 75 years, but considering also some problematic situations (sickness, pregnancies, etc), we could calculate that a vessel is useable roughly 50% of its lifetime.

Thus, the minimal self-replenishing herd size is 50, which means an average of 25 usable vessel. This can sustain around 12 vampires on an average 2BP/night rate.

It would be highly useful to blood bound them.

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Since you both have your own answer, rather than arguing in the comments on each other's posts, please focus on improving the case made by your respective answers on the points on which you differ. – SevenSidedDie Nov 22 '15 at 22:55

It depends on what quality of life you want for the victims. You can routinely take much more blood from the humans than medical guidelines suggest, though the humans will not like it very much. And is the vampire going to provide his victims with a healthy and iron rich diet? Or are the poor buggers foraging for moss to survive? that affects the quality of blood. In general it's better to have a larger v:h ratio, hundreds to one, so freak mischance or evening binging doesn't wipe out the herd. Minimiums are fragile things.

Does the vampire want to throw an occasional party for his vamp friends? Better lay in some extra humans; those warm blood fountains and blood puddings take a lot of raw materials. It's simpler if he just wants to subsist.

But the larger the population, more likely it is that someone gets born who gets fed up, so to speak, with being bitten every few months to years, and eliminates the vampire. That puts downward pressure on the ratio.

Thje simplest solution is a wandering vampire who can bite and move on; the world is wide and rich in blood, and the same scenery gets old after a thousand years, anyway. A wandering vampire never has to worry about running low on humans, or uppity local heroes catching him, so the population question is safely moot.

If you insist on a non-travelling vampire, I'd probably handwave up a 500:1 ratio, because it's a little less than double your minimium number and gives a safety margin; and then you're on the hook to explain why the population puts up with him. Dracula, in the end, travelled.

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There are some good points in here, but it doesn't really address the scenario as posited by the OP. – Bobson Jul 11 '14 at 20:31
Afaik the OP wants here calculations and not phylosophy. – Morning Star Nov 14 '15 at 8:23

Rules-wise? You spend one point of blood to wake up every evening. Assuming you never spend any blood, this means you need one point of blood each night. Otherwise healthy mortals recover one point of blood every day. From this, we can deduce that a vampire not spending blood on anything but waking only needs one person in their herd to feed on. This mortal will, of course, spend their whole life massively unwell from the constant blood loss. It's probably safer to have two, so that health issues in your herd and the need to spend blood don't mess things up.

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Question assumes frequent use of additional points, plus recovery time of four months, not one day. Can you give rules citations for the latter and rework to handle the former? – TuggyNE Jun 8 at 7:46