Fantasy genetics question

[Recherché]

In one of my games for various reasons almost every elf and half elf has been killed. The sole survivors (as far as we know) are 5 full blooded elves, 3 males and two females and one of the men is already past 500 and relatively elderly. Assuming that we can find interested humans, elven reproduction rate is similar to humans and that half elves are fertile, is it possible recreate a stable breeding population of elves or mostly elves and if so how?

[Brother Oni]

In one of my games for various reasons almost every elf and half elf has been killed. The sole survivors (as far as we know) are 5 full blooded elves, 3 males and two females and one of the men is already past 500 and relatively elderly. Assuming that we can find interested humans, elven reproduction rate is similar to humans and that half elves are fertile, is it possible recreate a stable breeding population of elves or mostly elves and if so how?

You're essentially looking at the minimum viable population number, which for humans (assuming no significant harmful genetic defects) is about 160 people to sustain itself over a 200 year period.

Some clarification is requested though:
What does 'reproductive rate is similar to humans' mean exactly? Is an elf female limited to human total fertility rates, so those two elf females will cap out at ~7 offspring each over their total lifespan? Is the gestation period and time until sexual maturity the same as humans?
What constitutes a 'mostly elf'? Anything with 50% elf parentage, or can it be lower?
Life span and fertility details - SRD20 says that High elves are considered venerable at 350yrs, so presumably those elf females will only be fertile from about 25 to 175 years old.

Edit: my answers are solely from a biological point of view where the individuals are just breeding machines - cultural and societal constraints may apply as an elf male running an incestuous harem/family of daughter/wives for a few hundred years ala Craster from A Song of Ice and Fire is probably not going to be acceptable way of rebuilding the population.

[Trekkin]

It would also be helpful to verify that elves are diploid organisms producing haploid gametes. I've seen games playing very fast and loose with genetics before that had tetraploid elves and triploid half-elves, and used ploidy as the marker for whether an individual counted as half-elf or not and an explanation for why there were no 1/4 elves and so on. Unlikely, but it will affect the math here.

EDIT: Also, how high-magic is the setting? Geneforge-level biotechnology would make this a non-issue, but I'm assuming we're closer to D&D standard.

[Recherché]

Elves have similar gestational periods to humans and maturation rates to humans but due to longer lives can have many more total offspring.

I should mention our two elven women are in their late twenties and early forties and the two younger men are in the same range.

I'd be willing to accept anything over 50% elf as a partial success but 75% or more as a full success.

[Trekkin]

Elves have similar gestational periods to humans and maturation rates to humans but due to longer lives can have many more total offspring. [...]
I'd be willing to accept anything over 50% elf as a partial success but 75% or more as a full success.

We're going to need to know their age categories to correctly map the decline of their fertility with age, then.

75% elf is actually pretty easy to achieve with just the two male elves. Assuming they're unrelated, each one could simply father as many half-elves as possible, at which point their half-elf children could have children with the half-elf children of the other male elf. One-fourth of the resultant grandchildren will be pure elves if "elf" is a single allele; for arbitrarily many alleles evenly distributed through the genome, each carrying an equal amount of elfness, on average 100-n% of the offspring will be n% elf, assuming my math is right, so 25% of what will surely be many, many possible offspring will meet your elf threshold if you randomly match the half-elves. Having elfier ones have more kids would help, though.

However, I believe even the elfiest ones will be first cousins (after some back-and-forth editing) with every other part-elf created by this process, since they share two grandparents and are thus half double first cousins. 12.5% coefficient of relationship is not good.

[factotum]

Even with the additional lifespan and thus period of fertility I don't see this being remotely viable. Either you're going to end up with significant amounts of inbreeding, with the known bad effects *that* can have, or else the elven strain is going to become so dilute that the species will effectively cease to exist--you'll have a few humans around with pointy ears and slightly longer lifespans than normal, and that's about it.

[hamishspence]

Inbreeding has its bad effects - but it's not a one-way ticket to extinction - it's possible for a small population to survive a period of inbreeding - a population bottleneck - and expand back up to "thriving size" levels:

https://en.wikipedia.org/wiki/Inbreeding

[Brother Oni]

We're going to need to know their age categories to correctly map the decline of their fertility with age, then.

75% elf is actually pretty easy to achieve with just the two male elves. Assuming they're unrelated, each one could simply father as many half-elves as possible, at which point their half-elf children could have children with the half-elf children of the other male elf. One-fourth of the resultant grandchildren will be pure elves if "elf" is a single allele; for arbitrarily many alleles evenly distributed through the genome, each carrying an equal amount of elfness, on average 100-n% of the offspring will be n% elf, assuming my math is right, so 25% of what will surely be many, many possible offspring will meet your elf threshold if you randomly match the half-elves. Having elfier ones have more kids would help, though.

However, I believe even the elfiest ones will be first cousins (after some back-and-forth editing) with every other part-elf created by this process, since they share two grandparents and are thus half double first cousins. 12.5% coefficient of relationship is not good.

If I've calculated it correctly, adding the other two elf females in (assuming all their children have different human fathers), only staves off the issue by a generation, assuming no parent elf is breeding with any offspring that's a direct descendant. That said, if you only bred the grandchildren with the parent elves, you would have a great-grandchild population pool of 75% elf derived parentage with no inbreeding (yet).

Depending on the number of half elf children, this may be enough to hit the minimum number required for a viable population (as long as there's enough alcohol for the grandchildren to forget 'family time' with elf grand uncle/aunt).

This is also assuming a strict breeding regime - the different ages of the offspring within a generation is likely to cause random matching between the varying children levels - by the time the great grand children are sexually mature, there's going to be a number of children and grandchildren about the same age.

Even with the additional lifespan and thus period of fertility I don't see this being remotely viable. Either you're going to end up with significant amounts of inbreeding, with the known bad effects *that* can have, or else the elven strain is going to become so dilute that the species will effectively cease to exist--you'll have a few humans around with pointy ears and slightly longer lifespans than normal, and that's about it.

Further to hamishspence's comments, inbreeding is only bad where there are nasty recessive genetic disorders in the current gene pool or there are significant external factors that promote genetic diversity (for example, disease). Generally, if there's an autosomal recessive disease that's lethal, then the first generation will have the fewest numbers as they all die off, leaving the ones who are either heterozygous or homozygous dominant. Over time, the recessive gene simply gets bred out and genes that are useful to surviving in the current environmental are promoted.

[ThurlRavenscrof]

Inbreeding has its bad effects - but it's not a one-way ticket to extinction - it's possible for a small population to survive a period of inbreeding - a population bottleneck - and expand back up to "thriving size" levels:

https://en.wikipedia.org/wiki/Inbreeding

Yes I think the main problem is the limited (basically 4 individuals!) gene pool. Time doesn't really matter at this point. Take cheetahs for example. A long time ago, all cheetahs were wiped out for various reasons except for like... Fewer than a dozen. As a result, cheetahs have had genetic problems and almost no genetic diversity ever since. It's EXTREMELY difficult for a species to bounce back successfully from that.

I highly encourage you to read this site as it might answer some questions
https://cheetah.org/about-the-cheeta...tic-diversity/

[Recherché]

It would also be helpful to verify that elves are diploid organisms producing haploid gametes. I've seen games playing very fast and loose with genetics before that had tetraploid elves and triploid half-elves, and used ploidy as the marker for whether an individual counted as half-elf or not and an explanation for why there were no 1/4 elves and so on. Unlikely, but it will affect the math here.

EDIT: Also, how high-magic is the setting? Geneforge-level biotechnology would make this a non-issue, but I'm assuming we're closer to D&D standard.

1/4 elves and 3/4ths elves do exist in setting, its just that they're phenotypically close enough to pure humans or pure elves that its hard to tell at a glance. Speaking of which the GM has informed us that there may still also be some humans with low levels of elven descent (less than 25%) left in the world but it would be a little bit of a pain to track them down. Question is whether that would be worth it.

Setting is pathfinder with small amounts of 3.5 and fairly high levels of arcane magic but limited divine magic. We can get access to anything with a 12th level or less arcane caster pretty easily. We might be able to de-age the old man or temporarily switch the sex of our survivors but it would take resources so we'd rather not do so unless it would make an impact.

Yes I think the main problem is the limited (basically 4 individuals!) gene pool. Time doesn't really matter at this point. Take cheetahs for example. A long time ago, all cheetahs were wiped out for various reasons except for like... Fewer than a dozen. As a result, cheetahs have had genetic problems and almost no genetic diversity ever since. It's EXTREMELY difficult for a species to bounce back successfully from that.

I highly encourage you to read this site as it might answer some questions
https://cheetah.org/about-the-cheeta...tic-diversity/

I know we don't have enough elves, the question is whether we could use a near unlimited supply of humans to compensate and create a stable population of elfy-enough.

[ThurlRavenscrof]

1/4 elves and 3/4ths elves do exist in setting, its just that they're phenotypically close enough to pure humans or pure elves that its hard to tell at a glance. Speaking of which the GM has informed us that there may still also be some humans with low levels of elven descent (less than 25%) left in the world but it would be a little bit of a pain to track them down. Question is whether that would be worth it.

Setting is pathfinder with small amounts of 3.5 and fairly high levels of arcane magic but limited divine magic. We can get access to anything with a 12th level or less arcane caster pretty easily. We might be able to de-age the old man or temporarily switch the sex of our survivors but it would take resources so we'd rather not do so unless it would make an impact.



I know we don't have enough elves, the question is whether we could use a near unlimited supply of humans to compensate and create a stable population of elfy-enough.

Yes I know. But you said you wanted 50% to 75% elf. That would not be possible. Maybe if 12.5% elf or 25% elf would be sufficient then it could be done

[Trekkin]

I think I may have a non-magical, non-intergenerational-incest solution to the inbreeding problem, albeit one that needs a lot of people to pull off and is horrifying, since like Brother Oni described this assumes everyone's perfectly willing and the numbers required get large.

Assuming that elven fertility declines at a rate proportionally slower than human fertility to match the differential in lifespan (and, therefore, a 350-year-old elf is as reproductively healthy as a 70-year-old human) and taking medieval infant mortality and miscarriage chance into account, I calculate that a 20-year-old and 40-year old female elf could together have as many as 214 children survive to adulthood over a 200-year period on average. Similar assumptions suggest the male elves of identical age could together father 180,224 children over a 330-year period.

Spoiler

Show

Suppose we call the two males M1 and M2, and the two females F1 and F2. If the female elves only have pure elf children, that means that over this 330-year period we can expect, on average, 56 surviving children of M1 and F1, 56 M2xF1, 50 M1xF2, and 50 M2xF2. Assuming perfectly even distribution across sexes, the maximum possible number M1xF1-M2xF2 crosses can together produce up to 6010 pure elven children; the same holds for M1xF2-M2xF1 crosses. That's 12,020 elves over a ~360-year period, all of them double first cousins but also pure elves and none of them inbred. This is the last time both those things can be true.

That still leaves M1 and M2 able to father 180,000 half-elves between them. Assuming that M2xF1/M2xF2-M1xH(n) (and, equivalently, M1xF1/M1xF2-M2xH(n)) crosses are prioritized and making the same assumptions about half-elf fertility, we can optimistically expect a resultant cohort of about 1.1 million people, collectively three-quarters elf with three grandparents in common and 0% inbred.

At that point we run into the question of double first cousin problems, and modifying our mortality assumptions to take the increased risks into account...the full elf grandchildren and three-quarter elf grandchildren could collectively expect some 3.9 million 7/8ths elves to reach adulthood, together with 378,000 full elves. The cycle keeps repeating on a larger and larger scale.

This suggests a strategy that requires no magic, just very accurate record keeping. Preferentially crossing pure elf males to the most elven females available in that generation (and vice versa, although the time differential makes the stated way more likely) makes as many offspring as elven as possible, which allows for beating the odds of increased mortality through sheer numbers; when that fails, there are as many outcrossing options with as much elf DNA as possible to fall back on until at some point there's enough additional diversity for random mutation to take over. Regular exposure to minimally toxic mutagens could hasten the arrival of that point, although it's best delayed until the second generation to compensate for the increase in mortality. The exact percentage elf of the minimum viable population is hard to predict a priori, but I don't see why 93.75% shouldn't eventually be achievable after an arbitrarily long time.

Again, I have to emphasize that there's no way to treat people like this that won't be chillingly awful. As a purely theoretical exercise, the numbers suggest that elven longevity and the fecundity it allows should ameliorate the worst consequences of inbreeding while amassing part-elves as a backup plan, but any actual implementation would involve treating millions of elves and part-elves and humans like nothing more than anonymous gene carriers. Case in point: among the assumptions I made for the above math are Rings of Sustenance to minimize time spent sleeping and the use of Raise Dead and Regenerate as appropriate to deal with complications in childbirth, and unfortunately most ways of cutting back on the horror also significantly lessen the percent elf of the eventual minimum viable population. At "best", this is Brave New World-style child manufacturing as overseen by the Bene Gesserit, and even that is going to produce millions upon millions of part-elves for which the program has no use.

[factotum]

Further to hamishspence's comments, inbreeding is only bad where there are nasty recessive genetic disorders in the current gene pool or there are significant external factors that promote genetic diversity (for example, disease).

Well, disease is a kind of important consideration, isn't it? Diseases mutate all the time, so if a disease develops that has particularly nasty effects on people of the specific genetic make-up of your five people, it will probably wipe them and their descendants out. That's part of the reason why there's a minimum viable population number, as you mentioned earlier--because a population too small doesn't have sufficient genetic diversity to avoid getting steamrollered by diseases that develop down the line.

[Jallorn]

I am not terribly well versed with biology, but I can theory craft. I lack a good way to really crunch numbers right now though, so some of it will have to wait until I get home.

Let's assume best case scenario: resources are essentially infinite and any amount of children can be cared for. So, we have two female elves who should be producing solely elven children. Assuming elves live to around 700, we might also estimate that menopause would likely occur around 500-550. Again, assuming best case, that gives around 530 and 510 years of fertility for our two females. In months, that's 6360 and 6120. If we push things, we could maybe push constant pregnancy for a child every ten months (9 gestation, 1 down time for recovery) and 1248 full elven children before this first generation cannot produce more kids. This might be rather excessively hard on the mothers, however, so let's pull things back to just one child a year, for 1040.

At the same time, the male elves can father many more children to human and half elven mothers for a great deal longer. I would say that all the males should father children with both mothers for maximal generic diversity, but that and human or part elven mothers should be more exclusive since we would expect more than sufficient diversity on that front. With around 200, 680, and 660 years before death, that's 18,480 months of life. If we assume an (optimistic?) average of 1 child fathered per month per male, and subtract the already calculated elven children, we get 17,440 part-elven children; genetically ideally they would all be to different mothers, but logistically and realistically, probably not. Still, more than just the 33 initial mothers.

Of course, given similar maturity rates to humans, many of this second generation are having kids before their parents are done, but that's style of the math beyond my abilities to keep track of right now. Still, for the first century and a half (two centuries if we're lucky) we have six categories of full elves based on mother and father. For any individual elf 1/3 of the population is not inbreeding. I can't figure out if the females elves should go exclusive yet right now, but male elves should still be fathering children with as many other women as possible still. At least one elven woman, and preferably part elven mostly, but a few human mothers would also be good fit maintaining diversity of genetics.

As a general rule, women, full or part elven, should favor more elven fathers, while those males should just be trying to have as many children as possible. A heavy culture of centralized records of lineage and probably harsh and controlling in case of genetic defects (but also resource providing to ensure maximal health) government would probably make the whole process more successful. This situation could do a real number on elven culture. Males get a fair bit of privilege on the side of multiple mates, but daughters are more valuable to the society because fewer male elves and more female elves is better for having more full elven children. There's also going to be a heavily internalized caste system by the time the system is stable based on the purity of one's "elfness."

Of course, the 90% elves will actually be far more genetically diverse and successful than the pure elves.

[Trekkin]

Well, disease is a kind of important consideration, isn't it? Diseases mutate all the time, so if a disease develops that has particularly nasty effects on people of the specific genetic make-up of your five people, it will probably wipe them and their descendants out. That's part of the reason why there's a minimum viable population number, as you mentioned earlier--because a population too small doesn't have sufficient genetic diversity to avoid getting steamrollered by diseases that develop down the line.

Yes, but those mutations can happen between individuals as well as between generations. Thus the strategy above of producing as many part-elves as rapidly as possible: that's as many sets of random (if not uniformly distributed) mutations occurring in parallel as possible, in the hopes that some fraction of them will be to something like the MHC. Genetic diversity takes less time to develop than you might expect.

EDIT: Jallorn: we seem to be approaching the problem similarly. Incidentally, I assumed Pathfinder elf age categories; given a twenty-year generational cycle, the initial four's great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-grandchildren are born before they stop.

[Jallorn]

Side note: I am totally building a setting based around the consequences of this idea of an elven genetic bottleneck.

[Jallorn]

Yes, but those mutations can happen between individuals as well as between generations. Thus the strategy above of producing as many part-elves as rapidly as possible: that's as many sets of random (if not uniformly distributed) mutations occurring in parallel as possible, in the hopes that some fraction of them will be to something like the MHC. Genetic diversity takes less time to develop than you might expect.

EDIT: Jallorn: we seem to be approaching the problem similarly. Incidentally, I assumed Pathfinder elf age categories; given a twenty-year generational cycle, the initial four's great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-grandchildren are born before they stop.

Indeed. I was using the old 3.5 venerable at 700 (as I recall it and recall (all without double checking) that venerable is about where death is expected) and the fact that there is an old, but not yet too close to death, elf who is already 500.

And add mentioned, I can't do that much math here, so yours is likely far more precise. I made a lot of assumptions. And based the age of menopause on the idea that 700 elf=70 human. Therefore 50=500. Then I allowed a little optimism based on elven longevity and extended a bit.

[Recherché]

There's actually a little more possible genetic diversity if we do decide to use Alter Self to temporarily turn the female pure bloods into male versions of themselves (GM has ruled that alter self does not change your genetic structure but with a decent caster level and duration you can get someone pregnant, the offspring will just be all daughters.) This might actually lead to women who are able to shapeshift being the most reproductively valuable people over time.

And yeah there's no way we're going to be able to persuade our survivors to go along with some of the more horrifying schemes. They're already protesting being treated as just breeding stock before we start talking about the incest and large numbers of abandoned surplus children.

[Jallorn]

There's actually a little more possible genetic diversity if we do decide to use Alter Self to temporarily turn the female pure bloods into male versions of themselves (GM has ruled that alter self does not change your genetic structure but with a decent caster level and duration you can get someone pregnant, the offspring will just be all daughters.) This might actually lead to women who are able to shapeshift being the most reproductively valuable people over time.

And yeah there's no way we're going to be able to persuade our survivors to go along with some of the more horrifying schemes. They're already protesting being treated as just breeding stock before we start talking about the incest and large numbers of abandoned surplus children.

Guaranteed daughters is great except that these daughters will share all the other elves' mothers genetically. This us really useful for the the current makes to be able to father more pure elves, but beyond that it's of uncertain value. I'd have to do math.

[Brother Oni]

Well, disease is a kind of important consideration, isn't it? Diseases mutate all the time, so if a disease develops that has particularly nasty effects on people of the specific genetic make-up of your five people, it will probably wipe them and their descendants out. That's part of the reason why there's a minimum viable population number, as you mentioned earlier--because a population too small doesn't have sufficient genetic diversity to avoid getting steamrollered by diseases that develop down the line.

Well 5 elves and an infinite number of available humans. It's only if something comes along that specifically targets the elfy bit that it becomes a problem.

That said, this is a D&D setting where Remove Disease is only a 3rd level spell, well within the 12th level caster limitation that Recherche gave (although she did mention that divine magic is limited).

I'm not too familiar with Pathfinder (or D&D in general past the Red Box), so some random questions:

Does Remove Disease work for genetically inherited ones?
Is it possible to introduce new elf genetic material into the gene pool with Polymorph (and if required, Permanency) shenanigans?

Side note: I am totally building a setting based around the consequences of this idea of an elven genetic bottleneck.

It may not amount to much - we've had similar sorts of bottlenecks resulting to a single common ancestor as evidenced by Mitochondrial Eve and Y-Chromosomal Adam.

[Recherché]

GM has ruled that polymorph and other shape changing shenanigans do not change your genetics (this is how half dragons come into existence as well as a few of the other odder halfs.)

Remove disease only works on infectious agents and parasites. Regenerate would fix genetic deformities but we're not going to have regular access at all. Heck we don't even have great access to reincarnate and raise dead.

[Trekkin]

And yeah there's no way we're going to be able to persuade our survivors to go along with some of the more horrifying schemes. They're already protesting being treated as just breeding stock before we start talking about the incest and large numbers of abandoned surplus children.

I had hoped that would be the case, to be honest. Concerted attempts to "repopulate the species", when the species in question is sapient, are not pleasant.

Really, the elven species is already dead. The relictual population you've gathered represents a statistically insignificant fraction of elven genetic diversity, cultural experience, and institutional memory; moreover, it is mathematically impossible to reestablish the necessary genetic diversity in a timeframe that allows for direct cultural transmission without resorting to at least some recourse to the methods described earlier. By the time sane rates of normal reproduction could see 75%+-elves regularly popping up among the half-elves, everyone who could teach them how to act like elves will be long dead -- and it sounds like they're aware of that.

Your best bet, then, is to avoid as much as possible the time limit implied by living organisms; make at least one box of gentle repose and put some tissue samples inside (blood is symbolically appropriate, but do make sure you get at least a cubic inch in case you need a clone spell someday), then have your elves get to writing down as much as they can about what elves used to be like. This is assuming they're unwilling to become intelligent undead, which seems entirely in keeping with their predilections so far.

Once you've got that, just wait, I guess; any shenanigans we could suggest to create enough elf zygotes are still going to run afoul of their morals. Perhaps one day the party will be high enough level to use clone/magic jar shenanigans to fill cloned elf bodies with placeholder souls and thereby give them time to mutate; theoretically the clone should mutate considerably in growing from a tiny bit of flesh to a full-grown body, but that might not fly with your DM. You'll want to make a custom item of clone so you don't need to pay 1000 gp per clone, but then you could theoretically just cycle a small number of willing souls through the entire population of bodies to meiotically produce new elf babies with new elf souls all ready to be taught how to elf by the documents their elders left for them.

[Jallorn]

This might not be so terrible as we thought actually. I did some visual respresenting of pairings and color coded their elf-ness. From that first generation we have 7 categories of full elves, and three of half elves. After the second generation starts producing, along with the first generation, we have 27 more categories of full elves, 15 of quarter humans, and 6 of half-elves. Then, one more generation gives us 42 more full elves, 30 12.5% humans (practically full elves), 30 more quarter humans, and 18 more half-elves. And that's not counting the breeding of half-elves with half-elves or even half-elves into human populations.

This all assumes that all of the original generation are still breeding prolifically, (which seems well within the realm of possibility for all but maybe the oldest male) but this is also all without inbreeding. Now, inbreeding is eventually inevitable, but along with a continued influx of human genes (which could, by the way, be quite diverse genetics from lots of different pools) and a vigilant population that is willing to abandon those with recessive flaws (even if only by preventing them from personally producing more children), they could manage sustainability.

Honestly, by the third generation, although the elven genetics are, of course, all from the same five individuals, a lot more freedom for breeding partners opens up. There is still some risk of recessive flaws, but it's low enough with the influx of human genetics and individual mutation. Indeed, if we're lucky enough to have five seed elves with a lower than normal number of recessive risk markers, and they are lucky enough to pass those on rarely, we could have a very healthy community by this point. Inbreeding to some extent is not as bad as we often think it is, from a genetic viewpoint, at least according to a quick review of some research on the internet.

By the time the oldest elf dies (again, I'm assuming he lives another couple centuries, still not sure if that's accurate)... well, let's see if we can do the math. The first generation of new elves can be expected to reach childbearing in about twenty to twenty five years. Another twenty five after that and we have another generation of that first grouping, and a generation of the second grouping. Another twenty five years and we have a generation of groups 1, 2, and 3. So in two centuries, we have four generations of group 1, three of group 2, two of group 3, and another generation beyond that. What is the size of a generation? Well, that first generation is only around ten elves, but many more more half elves. The second generation is more like twenty or thirty of the first group (both the ones born twenty five years ago, and the ones who had already been born but not yet reached maturity then), and maybe twice that of the second? And we get some nice quadratic growth from there. Easily a few thousand elves and mostly-elves by two centuries. It's still a risky population size, but by the time the rest of the five founders die another few centuries later, I think it's reasonable to call the population no longer at risk, assuming some catastrophe doesn't befall them before then.

And I'd say with such long lives to write and teach, these five elves (and any number of human, or other race, scholars of elves) have plenty of time to inform the children of what their history and heritage are.

[ThurlRavenscrof]

Really, the elven species is already dead. The relictual population you've gathered represents a statistically insignificant fraction of elven genetic diversity, cultural experience, and institutional memory; moreover, it is mathematically impossible to reestablish the necessary genetic diversity in a timeframe that allows for direct cultural transmission without resorting to at least some recourse to the methods described earlier. By the time sane rates of normal reproduction could see 75%+-elves regularly popping up among the half-elves, everyone who could teach them how to act like elves will be long dead -- and it sounds like they're aware of that.

Agree. And this isn't even considering the futility of long term survivability. The simple fact is that the more humans you add, the more genetic diversity you get which is good but also the less "elf" each individual is (at least less than 25% if you want genetic survivability). But either decision you make... you'll eventually (after a thousand years or so) run out of elf blood. The same thing happened with neanderthals. Long term, humans will be slightly more elf like but you can't revive and healthy and stable population from 5 people who don't want to be treated like incestual breeding machines.

And one could make the argument that elves were willing to be incestual breeding machines, then elf kind is already dead.

[GreatWyrmGold]

I've seen games playing very fast and loose with genetics before that had tetraploid elves and triploid half-elves, and used ploidy as the marker for whether an individual counted as half-elf or not and an explanation for why there were no 1/4 elves and so on.

Eurgh. Apparently having "elfiness" as a single-gene trait wasn't sciencey enough for them...I hate when authors use science words and concepts they clearly don't understand to try and give their technobabble more weight among the equally-ignorant. Do your homework or just handwave it—either way works, but trying to technoBS your way through is just going to tick off the informed—and potentially misinform the uninformed!
Sorry. Just a rant.

Further to hamishspence's comments, inbreeding is only bad where there are nasty recessive genetic disorders in the current gene pool or there are significant external factors that promote genetic diversity (for example, disease). Generally, if there's an autosomal recessive disease that's lethal, then the first generation will have the fewest numbers as they all die off, leaving the ones who are either heterozygous or homozygous dominant. Over time, the recessive gene simply gets bred out and genes that are useful to surviving in the current environmental are promoted.

Um...everyone has zillions of rare recessive genetic disorders which would be lethal or debilitating when homozygous. It's just that they're rare enough that, without a recent common ancestor between you and your significant other/germline donor of choice, the chance of any "bad gene" matching up with a matching pair is far lower than that of a miscarriage. But with that common ancestor...well, that's why genetic disorders pop up seemingly out of nowhere in old European monarchies.
And you can't breed out that kind of problem—they keep popping back in. Mutations are shockingly common, and some of them are going to be bad. In general, the number of "bad genes" vanishing by chance is about the same as the number coming into the gene pool by mutation.



My personal field of expertise (relatively speaking) is biology, so I thought I'd be able to help out here. Unfortunately, all the good points have been made, so I'll have to do with adding a dose of one of my hobbies—sociology.
Assuming that elves are considered "superior" to humanity in some way (and between precedent and the fact that we can assume plenty of interested humans, they probably are), elf-blooded individuals are probably going to be considered higher-class than non-elf-blooded ones. If these five elves don't go for immortality or engage in some overly-elaborate plan to preserve genetic diversity (which would probably need a relatively modern understanding of genetics), they (or their descendants, if they all marry each other) will presumably find some of the best human mates to marry (adding in psychological, social, economic, and/or romantic compatibility to the mix), which will only further bolster their descendants' image. Given a little serendipity or forethought, these spouses could easily be people of great social standing (nobles, rich merchants, adventurers, whatever), giving children both inherited titles/riches/glory/etc and elven blood. A sort of social hierarchy could easily come to be, with the rich and powerful having significant amounts of elven blood and the teeming masses having only what trickles into their gene pool through bastards and the occasional princess/pauper relationship that ends with the "princess" losing status. If there is some obvious and clear way to tell how elfy one is (ear length, magical acuity, sacred tree reactions, what-have-you), this "elfiness" could easily be used as another measure of desirability; "lower-upper-class" aristocrats might boast of how elfy their daughter is when trying to convince a prince to marry her. And so on and so forth.
But this is all down the line...assuming that the timeframe of your story is already set in stone, of course.

[FreddyNoNose]

We're going to need to know their age categories to correctly map the decline of their fertility with age, then.

75% elf is actually pretty easy to achieve with just the two male elves. Assuming they're unrelated, each one could simply father as many half-elves as possible, at which point their half-elf children could have children with the half-elf children of the other male elf. One-fourth of the resultant grandchildren will be pure elves if "elf" is a single allele; for arbitrarily many alleles evenly distributed through the genome, each carrying an equal amount of elfness, on average 100-n% of the offspring will be n% elf, assuming my math is right, so 25% of what will surely be many, many possible offspring will meet your elf threshold if you randomly match the half-elves. Having elfier ones have more kids would help, though.

However, I believe even the elfiest ones will be first cousins (after some back-and-forth editing) with every other part-elf created by this process, since they share two grandparents and are thus half double first cousins. 12.5% coefficient of relationship is not good.

Since this is fantasy and they are elves, it could be something completely different than what we have here on Earth (aka the real world). Perhaps when population is low they start having multiple births.

[Draconi Redfir]

pretty sure that no matter which way you bend it, half-elves breeding with half-elves will just bare more half-elves. you can't get two half-elves to give birth to a full-elf, genetics don't work that way.

[BWR]

pretty sure that no matter which way you bend it, half-elves breeding with half-elves will just bare more half-elves. you can't get two half-elves to give birth to a full-elf, genetics don't work that way.

Mystara at least has one realm of true-bred half-elves. As far as fantasy genetics, it works however the writer wants it to work. If you want incest to have no deleterious effects or even strengthen the bloodline, as in Tanith Lee's Birthgrave trilogy or the Juraians of Tenchi Muyo, then inbreeding isn't a problem. If you want magical lizards to be able to interbreed with pretty much anything, then they can.
It's not as though every other aspect of physics isn't routinely violated sixteen ways from Sunday in many settings, so there's no need to take too much care in getting genetics as close to the real world as possible unless you really, really want to.

[hamishspence]

The idea would be that genes aren't passed on evenly.

So, two half-elves who have a lot of offspring, would have some who look more elven, and some who look more human, and some who are close to 50-50.

If only the "elfiest" half elves remain in the community, with the less "elfy" ones leaving it - and if looks reflect genes - then a selective breeding program over a very long period, will lead to larger, pointier ears on average, better low light vision on average, and so forth, until the population ends up being close to the original elven on.

[GreatWyrmGold]

pretty sure that no matter which way you bend it, half-elves breeding with half-elves will just bare more half-elves. you can't get two half-elves to give birth to a full-elf, genetics don't work that way.

Assuming an indefinite number of elfy genes, yes. But the more genes that get involved, the more it becomes like breeding tigers and lions and the less it becomes like breeding blondes and brunettes. Ligers and tigons aren't very fertile, but half-elves apparently are. With that, there's a fair chance for some children to be more like 40/60 or 30/70 mixes (numbers chosen arbitrarily), and if the 60-70% mixes have kids some might be close to 80% elf, and so on. But even with large numbers of genes, children would vary in "elfiness" (assuming that there's some way to quantify it, of course).
That naturally leads to inbreeding; see the rest of the thread for details and potential solutions.