Assuming good fortune and ideal conditions, which species are able to recover from a single organism? (By this, I mean successfully grow back to the height of their numbers)
Would most plants be able to? Would most animals? How about homo sapiens?
And which species would be able to repopulate back to their heights in the shortest amount of time? Longest?
If you’re talking mammals, your sole survivor better be a pregnant female.
Since Cecil says Life begins at conception, assume “good fortune and ideal conditions” could mean a fertile female with a gangbang creampie. That leads to a pregnancy with a multiple birth from different fathers.
A fertile female together with a sperm bank would suffice for H. sapiens, with a bit of luck.
You mean a fertile male cannot reproduce?! 35 years of wasted effort!!!
If it were me alone with embryos from a IVF clinic, or eggs, and the technology to bring them to term somehow (myself or surrogate), I wouldn’t do it. No way am I going create and raise a bunch of kids myself and leave them to make the same mistakes. We screw it up, then we’re through and I hope bonobos take over. And good riddance.
Can’t some female animals get pregnant by themselves?
I thought that we were noticing it with animals in zoos.
Aside from life forms with an asexual reproduction option, like many kinds of plants, bacteria, mould, and the like, the OP is asking about parthenogenesis: the ability of a multicellular organizm to “give birth” to clones of itself.
There are some kinds of lizard who can do this (whiptail lzard), along with bees and aphids, apparently.
There has been work on parthenogenesis in birds, which is interesting because, in birds, the female is the one whose genetics determine the sex of the offspring. The female is XY and the male is XX (but we use WZ and WW instead to differentiate them from mammals). So, in theory, a parthenogenic female bird could give offspring of both sexes. However, in this study, only males were produced.
Exactly how fast a population re-establishes itself depends on it’s reproduction and juvenile length. Bacteria re-establish quickly. Elephants, with their multiple years until sexual maturity and 2 year long gestation length, would not.
Hmm, what about plants that can self-fertilize? Would that be considered asexual, parthenogenesis, or a third option?
I thought that was a third option, to distinguish it from true asexual reproduction.
In my original post, I was using “asexual” in the layman’s sense of reproducting with only one individual. So, plants that can self-polinate would be included, but plants with distinct sexes would not.
If we start going into details on all the different vocabulary to describe sex, this thread will never end. 
I remember reading some speculation that the smallest a human community could possibly be and still have adequate genetic diversity to thrive would be about thirty people. And it would have to have some serious reproductive discipline to avoid destructive inbreeding.
What happens to other mammalian species, like dogs and lab rats, when you repetitively breed them to themselves? I thought that one of the selling points of certain breeds of lab animals was their genetic uniformity.
I thought the 30 people figure was to ensure success. If you stipulate good fortune and ideal conditions, I think fewer could succeed.
There’s also the question of what level of culling is acceptable. If weed out all of the “defectives”, those showing a negative recessive trait, then it won’t take very many generations to clean up the gene pool, but it will take many offspring each generation to get enough non-defectives.
The number of “defectives” from inbreeding is nowhere near as high as most people think. The odds are actually rather small even between 50% crosses such as brother and sister and father and daughter, less than one in a thousand IIRC.
But your other point is very true and the prime determinant of viable population size. If a population is breeding fast then you can get by with tiny numbers of individuals. Cheetahs are all believed to be descended form something like 7 individuals in the recent past and they’re doing just fine. If the population is multiplying rapidly then the off negative recessive trait thrown up by inbreeding is very rapidly swamped by outbreeding with the individuals who don’t carry that trait. All you need are two individuals provided they can reproduce very rapidly and the population continues to reproduce rapidly. Even if they both happen to carry negative recessive genes that will only affect 25% of their offspring, which is nowhere near enough to kill off even slow reproducing animals like humans. Within a few generations there will be more than enough non-carriers to eliminate the chances of inbreeding almost entirely.
The other issue however is that you now have very limited genetic variability. That poses a problem when the population is confronted with novel diseases and is far more likely to lead to extinction than the direct results of inbreeding.
As well as a couple of kinds of sharks
http://news.bbc.co.uk/1/hi/sci/tech/6681793.stm
That obviously depends on what you consider “defective”. There are some hereditary diseases which are more common than 1 in 1000 just from breeding in the general population, much less close relatives.
If a trait exists at a rate >1000 I would start to question whether it is a disease (in the sense of reducing reproductive fitness) rather than simply being a trait such as sickle cell and/or whether it is hereditary . It’s hard to imagine how a genetic disease could become so widespread if it was adversely affecting reproduction. Simple selection should the keep number well below that.
Can you tell us what disease you think is more common than one in a thousand in the general population? Haemochromatosis is usually considered the most common genetic disease with an incidence rate of about 2 per thousand. However that is a trait that confers resistance to anaemia and doesn’t normally affect people until after reproductive age so it’s irrelevant to this discussion. Cystic fibrosis is generally considered the second most common genetic disease, but its incidence is well below one in a thousand.
Not THAT fine; the entire species now has a very low endurance. And with such a low level of genetic variability, there aren’t any high-endurance cheetahs that can outcompete the others and breed endurance back into the species.
Can you define “just fine”? From this article:
Of course there are. This is like complaining that the entire three-toed sloth species has a very low speed and that there are no that there are no high-speed sloths that can breed sprinting back into the species.
This has absolutely zero to do with inbreeding. Both these species occupy niches at opposite ends of the speed spectrum of mammals and both of them are superbly, and hence obligately, adapted to that niche. The absence of sprinting sloths has nothing whatsoever to do with a lack of genetic diveristy. Sloths are as genetically diverse as any other species.
No sloths can sprint because sloths have become superb specialists of a slow-burn lifestyle and that precludes any sprinters. That doesn’t mean that some sloths aren’t slightly faster than others and wouldn’t be favoured if increased speed were a survival advantage. And exactly the same is true of cheetahs. Some cheetahs will have slightly better stamina than others and will be selected if that is beneficial.
In reality, like all specialist species, the sloth and the cheetah will probably become extinct if their specialistaions cease to be advantageous. It’s almost impossible to climb back down that evolutionary tree and exploit an alternative niche faster than the myriad of existing generalists. This is the peril of specialisation.
But this has absolutely nothing to do with inbreeding. Any specialist will face the exact same problems precisely because they are specialists.
I thought I already had in the post that you quoted: negative recessive trait thrown up by inbreeding is very rapidly swamped by outbreeding with the individuals who don’t carry that trait. The cheetahs problems are not caused in any way by negative recessive traits. They are caused by a lack of genetic diversity making them susceptible to disease, something else that I raised in the post that quoted from: The other issue however is that you now have very limited genetic variability. That poses a problem when the population is confronted with novel diseases and is far more likely to lead to extinction than the direct results of inbreeding.
I’m not sure what about that post confused you, but to make it clearer: despite being descended from an ancestral pool of fewer than 10 individuals cheetahs are doing fine. They are not suffering from what Chronos called “negative recessive traits”. That is what I quoted and what I was directly referring to in that post. That is what I mean by doing fine: they are non-defectives. Such defectives are actually perishingly small even in inbred natural populations and do not require the high levels of culling that Chronos thought was necessary.
The OP wanted to know what organisms could grow back to their original height in numbers form single survivor. Cheetahs only produce two cubs normally, but there survival from <10 ancestors shows that an animal like a cat or rat that produces litters of six or more could potentialy recover from a single pregnant female. I can’t see any reason why cheetahs couldn’t have recovered there original population size in a world where humans and climate allowed them to occupy their entire former range. Bit of a bummer going through that bottlneck just as agriculture was invented,.
Cheetahs do have very limited genetic variability. That poses a problem when the population is confronted with novel diseases and is far more likely to lead to extinction than the direct results of inbreeding. I really can’t make that point any more clear than I made it originally aside from stating quite clearly that extinction is not doing fine. However the OP explicitly assumed ideal circumstances. That means no disease, no conflict with human agriculturalists and so forth.
I guess the answer for the OP is that if we allow pregnant females then any mammal that produces large litters could recover from a single individual. Those that reproduce fastest will recover fastest, so rodents will fare better than cheetahs. I would guess that a rodent with a narrow range, such as an island rat, could rebound from a single individual in as little as a few hundred years.
For animals that produce only single offspring it gets harder to say for sure but potentially even something like a cow could rebound ion a few milennia.