To summarize: At this point, humanity is its own greatest extinction risk. If we don't destroy ourselves in the next century, we will almost certainly inherit the stars.
For a much deeper treatment of this subject, I recommend Global Catastrophic Risks, edited by Nick Bostrom and Milan Ćirković. The overarching point is straightforward (see the paragraph above), but the details of each threat are interesting on their own.
Humans will most definitely be the cause of human extinction on planet Earth. I would put my money on Homo sapiens not making it another million years on the surface of the planet.
Homo sapiens reached anatomical modernity about 200,000 years ago and began to exhibit behavioral modernity around 50,000 years ago.
I suspect that our descendants 1,000,000 years from now wouldn't consider themselves Homo sapiens- primitive, brutish creatures. (Consider how we feel about our ancestors from as recently as 50,000 years ago.)
Actually we can relate very well with the concerns of people from a few thousands years ago. Writings from ancient Rome, from ancient Greece are still very contemporary in many, many ways.
A million years is too far. Even if it doesn't happen by then, we are going to run out of energy, get killed by super bugs or hit by a asteroid.
The threat of human driven human extinction is more on the lines of a mutually assured destruction, weaponized nanotechnology or genetic engineering, irreversible climate conditions, over population of the planet etc.
A quote: " ... international policymakers must pay serious attention to the reality of species-obliterating risks."
Are these people all completely ignorant of evolution and science? No matter what happens in the future, one or another species-obliterating risk is a certainty. Here's why:
1. Our species has existed for about 200,000 years.
2. On that basis, and given our present knowledge of biology and evolution by natural selection, it's reasonable to assume that, within another 200,000 years, we will have been replaced by another species who either successfully competed with us, or into whom we simply evolved over time.
3. Human beings are a note, perhaps a measure, in a natural symphony. We're not the symphony, and we're certainly not the reason the music exists.
4. Based on the above estimate, there will be 10,000 more human generations, after which our successors will no longer resemble modern humans, in the same way that our ancestors from 200,000 years ago did not resemble us.
5. We need to get over ourselves -- our lives are a gift, not a mandate.
6. I plan to enjoy my gift, and not take myself too seriously. How about you?
"1. Our species has existed for about 200,000 years.
2. On that basis, and given our present knowledge of biology and evolution by natural selection, it's reasonable to assume that, within another 200,000 years, we will have been replaced by another species who either successfully competed with us, or into whom we simply evolved over time.
"
When our species had existed for around 5 years, does that mean it was reasonable to assume that within another 5 years, we will have been replaced by another species?
> When our species had existed for around 5 years, does that mean it was reasonable to assume that within another 5 years, we will have been replaced by another species?
You're missing the point that our species didn't arrive that quickly. From the perspective of 199,995 years ago, assuming a certain amount of intelligence, our forebears would make a similar assessment -- that they had assumed their present form some hundreds of thousands of years ago. And we have copious fossil records to support the idea of a typical duration for individual species before they disappear.
In any case, it doesn't matter which numbers one chooses within wide limits -- the fact is that our species will disappear, no matter what we do, within, say, 500,000 years at the most -- meaning our descendants will not be recognizable to use, could not interbreed with us, and would not be obvious kindred spirits to us.
We're a transient species, and we're not in charge, nature is.
That arguments sounds like a classic religious argument against evolution. 'If we came from the monkeys, why aren't currently monkey's turning into humans' like argument.
The answer is evolution is more like a fork/branch than modifications on the trunk. Mutations happen all the time, every cancer victim, is a victim of mutation. But when the gene begins to spread and take root rapidly, at some point we get that gene dominant among a species.
A lot will happen over the next 200,000 years. We will likely change in major ways.
But if you were to take this whole singularity thing seriously we may not even need all that. By 2045 you can live on eternally on the cloud.
Our planet needs to create at least one offspring with a good chance of sprouting a fresh batch of DNA based life on another planet before we send ourselves back into the stone age. If we don't, there are only so many shots left for us to become a space faring civilization again. If our species can't get off this planet. We may die as surly as an ant colony in the middle of the desert. DNA based life on this planet will halt, without anyone to carry on the carnival somewhere else in the universe.
This is serious business. If we don't fill the entire universe with efficient replicators to speed up the consumption of all energy to equilibrium. Then the reason the universe was created will have been for nothing. The stars must not be allowed to run down without our first harvesting them for our multitude of shenanigans.
> Our planet needs to create at least one offspring with a good chance of sprouting a fresh batch of DNA based life on another planet before we send ourselves back into the stone age.
I hate to break this to you, but evolution isn't about humans or dolphins or spacefarers, it's about genes -- evolution is genes replicating, using organisms as vessels.
In answer to the old question about which came first, the chicken or the egg, an evolutionary scientist answers, "a chicken is an egg's way to make another egg."
Also, at a more mundane level, by the time our descendants are scattered across all the local star systems, they will be so different from us that we won't recognize them or feel any special kinship.
But on reading your post to the end, I see you're probably kidding. Oh, well.
I believe that all life on this planet came from elsewhere in the universe. And only the life forms that can quickly reproduce and spread to other planets get to live on. Our meta species has not yet reached the time where we explode and spread our genetic material all over like a dandelion in the wind. Intelligent life on this planet is still inside the proverbial egg, and we are maybe 300 years from hatching.
> I believe that all life on this planet came from elsewhere in the universe.
One can argue that this is uncontroversial on the ground that life's precursors came from elsewhere. The only debate is what level of complexity is meant by "came from elsewhere".
> And only the life forms that can quickly reproduce and spread to other planets get to live on.
There's another, more likely explanation -- that life in some form naturally arises if the conditions are right, and there doesn't need to be a connection with another life-supporting environment. This isn't proven yet, it's just likely.
Eh. I dunno whether I am just optimistic, but let's try to remember that certainty isn't part of the scientific vocabulary; almost by definition science never seeks to provide a final answer on any subject and remains open to further inquiry/falsifiability.
So. I believe one of the reasons humankind is so awesome is that we have the capacity to be more than just a note in your natural symphony; we are constantly changing, creating and inventing— and I think it's entirely up to us whether we continue to flourish. Not to get all mystical, but perhaps in time the notion that we are 'the reason the music exists' will not seem super far-fetched. I guess I just think that human consciousness is so unique and cool that it is worth going to great lengths to preserve it, and to hell with what's considered 'natural'.
> Eh. I dunno whether I am just optimistic, but let's try to remember that certainty isn't part of the scientific vocabulary; almost by definition science never seeks to provide a final answer on any subject and remains open to further inquiry/falsifiability.
Yes, that's true, but my point isn't a scientific one, it's a mathematical one. Given enough time, the human species will disappear. It's an equation, not a theory open to empirical test -- but it's certainly supported by evidence from other species.
> ... and I think it's entirely up to us whether we continue to flourish.
This denies a role for nature, from which we sprang. Given that, if we "thrive" and are not outcompeted by some other species, then instead the form of our thriving will be to evolve to the point where present-day people wouldn't be able to recognize the outcome as human.
I say this based on the copious evidence buried in layers of rock that records billions of years of evolution of countless species, of which we are one.
> I guess I just think that human consciousness is so unique and cool that it is worth going to great lengths to preserve it, and to hell with what's considered 'natural'.
More New Age fantasy. When we try to improve on nature, because of our intellectual limitations we instead become nature's obedient servants.
Yeah I mean as long as there's historical continuity between our civilization and these hypothetical future human-like things, I'm totally on board. Not committed to humans as they are in 2014 sticking around forever. I think any disagreement between these views rests mainly on what we mean when we say extinction event. I would insist, however, that the notion of human consciousness being a phenomenon worth preserving as long as possible isn't some 'New Age fantasy', come on now.
> I would insist, however, that the notion of human consciousness being a phenomenon worth preserving as long as possible isn't some 'New Age fantasy', come on now.
But it is a New Age fantasy. A million years from now, no matter what course natural selection takes, any surviving species will almost certainly be so unlike us that we would not recognize them as even remotely kindred spirits.
I chose a million years to avoid a discussion about how long it might take for natural selection to naturally eliminate us entirely. In that future time, there might be super-intelligent species who would be repelled by what we regard as high intellect, or there might be simple-minded cockroaches. Or (who knows) there might be cockroaches who would be repelled by what we regard as high intellect. :)
There's a natural tendency to think of us as a permanent or special fixture of the earthly landscape. But that has no basis in reality -- we're a transient form with no special significance. To me, our relative insignificance makes who we are, and what we can do, worthy of reflection and a certain amount of gratitude toward the random workings of nature for creating us in the first place.
This is the most ridiculous comment here. You are literally arguing against the premise of preventing the destruction of the world. Screw that, I don't want to die, I don't want humanity to die, and I know few people who do.
Nothing is going to replace humanity if we kill ourselves first. Gradual evolution isn't want these people are talking about anyways, and there is no reason evolution is inevitable. Soon we will have the technology to control DNA however we want.
I feel a medium-term or maybe even short-term threat (in the next 10-30 years) not of extinction necessarily but of becoming completely irrelevant. People like to jump to the conclusion that artificial super-intelligence will want to eliminate humans. I don't think that is a foregone conclusion at all.
However, if (when) super-intelligent artificial general intelligence "arrives", that pretty much makes normal unaugmented humans the relative equivalent of chimps. It means that our opinions and actions are no longer historically relevant. We will be, relatively speaking, obsolete mentally disabled people running along doing relatively stupid things. http://www.youtube.com/watch?v=I_Juh7Xh_70
In order for our opinions and abilities to actually matter relative to the super-doings and super-thoughts of the new AIs, we really _must_ have this magical nano-dust or something that integrates our existing homo sapien 1.0 brains with some type of artificial super-intelligence.
So that is what I am worried about -- will the super-AIs show up before the high bandwidth nano-BCIs (brain-computer interfaces) or before I can afford them.
Of course, in the long run there may not be a good reason for AIs to use regular human bodies/brains at all and so that may be phased out for subsequent generations.
There are a lot of things to this Armageddon-through-AI equation. Firstly this thing called 'energy'. A paper clip maximizer will long reach its demise before converting a maximum part of planet to paper clips, merely because it needs a lot of resources to produce energy, and maintain itself too.
In fact true AI would not destroy anything. Because true AI would know it doesn't have sufficient data to make any such decisions.
There is more than enough energy on Earth alone to destroy humanity. Most likely an AI would want to maximize it's energy. Covering the entire face of the Earth with solar panels, or even building a matrioshka brain from the mass of the solar system.
An AI not specifically programmed to value human life would have no reason to keep us around. It'd either kill us because it sees us as a threat, competition, or just annoyance, or it would kill us by accident as it consumes all the resources it can.
The article talks about disasters that could eliminate humanity, but I wonder if humanity is more likely to become extinct in the sense of no longer being "homo sapiens."
For example, through a technological singularity or even just through accumulated gene therapy over generations.
I wonder if in the case of a technological singularity would you be able to tell that the original species was human? That is to say if we're at the point that we are augmenting our brains to that degree will the difference between a human/dolphin/great ape brain as a base be dwarfed by the technological layers on top of it?
That's getting a bit speculative as a question though. It was more of a thought on how much/how little we might need to change to even constitute not being human.
You could take the evolutionary viewpoint, where two branches of a species are considered to be distinct when they can no longer breed. Though with the current state of globalization I doubt that could happen... on earth.
But the human lineage doesn't need to split into branches for us to be replaced by another species -- we might instead simply evolve away from our present form sufficiently that present-day people would not be able to (a) recognize our own descendants as kindred spirits or (b) be able to breed with them (assuming an imaginary biological test in which one of us is propelled 200,000 years into the future).
Modern humans have existed for about 200,000 years. Therefore, natural selection being what it is, chances are in another 200,000 years we will no longer exist in our present form, but be replaced by a new species, one we cannot imagine.
Of course we should also wonder what we may become as we rise. We are no longer the foragers who began this climb, nor the farmers who climbed just a few floors below, and those ancestors would probably not be pleased with everything we have become. We’ll probably also have misgivings about what our descendants become. But hopefully we will on net be proud of them, just as our ancestors would probably be proud of us.
Okay, hold on a minute. When you say, "humanity and its extremely advanced descendants", when you link to an article containing the phrase "steps up the ladder", when you quote someone saying, "we should also wonder what we may become as we rise" [emphasis added], you're overlooking something basic about evolutionary theory that everyone needs to understand.
And that is that evolution is not necessarily a progression from less to more advanced, from less intelligent to more intelligent, or for that matter, from less anything to more anything.
Evolution is not a plan with a goal, it is a blind algorithm that chooses survivors, regardless of the survivors' traits, with the single requirement that they are the fittest for the environment in which they find themselves.
This talk about steps up the ladder and extremely advanced descendants is scientifically ignorant and a New Age fantasy. We are as likely to be replaced by cockroaches as by superbeings.
1. I was explaining the position of Bostrom, Hanson, and others. I do not completely agree with them.
2. I think you have misinterpreted their position. Bostrom and Hanson know quite a bit about evolution. They know that evolution is undirected and would eventually result in an organism we wouldn't recognize, let alone value. But they both think that we are entering a time in which we will no longer be bound by evolution. They think that humanity will soon be able to engineer minds, allowing us to improve their raw abilities while having them retain many of our own values.
On this point, I do agree with them. Evolution hill-climbs, so it gets stuck in local maxima and can't search the entire solution space. We're already building lots of stuff that could never evolve: radio, wheels, impellers, turbines, lasers, etc. In billions of years, evolution hasn't figured out a way to send signals faster than 0.000001c (300m/sec). That's how fast sound waves and nerve signals travel. As optimization processes go, it really is quite terrible. If we want to make better minds in any reasonable time-frame, we'll need to engineer them ourselves.
I understand it perfectly -- they're either as ignorant as their followers, or they're exploiting public ignorance.
> Bostrom and Hanson know quite a bit about evolution.
They either know nothing about evolution, or they're deliberately misleading their readers. Contrary to their writing, natural selection is not a race to the top, because it's not a race to any particular objective.
> But they both think that we are entering a time in which we no longer be bound by evolution.
Apart from revealing their inability to grasp evolutionary theory, this is an ignorant New Age fantasy. We will always be bound by natural selection, even when we actively participate in the process.
> They think that humanity will soon be able to engineer minds, allowing us to improve their raw abilities while having them retain many of our own values.
But that's also evolution. To argue that people meddling with genetics isn't evolution is to misunderstand evolution's scope.
> Evolution hill-climbs ...
You really need to stop thinking about natural selection as though it's a race to the top of the hill. This idea contradicts both evolutionary theory and copious observational evidence.
> We're already building lots of stuff that could never evolve [emphasis added]: radio, wheels, impellers, turbines, lasers, etc.
All these things exist in nature, even including the lasers, all of which evolved in nature:
All your examples have similar pre-existing embodiments in nature. And they all evolved.
> If we want to make better minds in any reasonable time-frame, we'll need to engineer them ourselves.
People doing engineering is an example of natural selection. There is nothing in the sequence of human events that isn't an example of evolution by natural selection.
All this talk about moving beyond evolution fails to grasp how evolution works in our lives. Even A/B testing of Web pages is an example of natural selection.
To summarize, these people you're quoting are simply pandering to low public taste -- they're either broadcasting their own ignorance or exploiting the ignorance of the public. Evolution doesn't work they way they claim, and their writing is a scientific laughingstock.
I don't know if you've read the writings of Bostrom/Hanson. You are very wrong in terms of both their message, and their purposes.
They do not misunderstand evolution. In fact, considering they're both respected professors, you might want to give them some amount of "benefit of the doubt". If you're basing your position about them based on one article, you really should at least consider the fact that you're misunderstanding them.
As for what you say about evolution, I have a hard time with what you call "evolution", because your definition seems to include literally everything that ever can or will happen on earth. So let's put aside the word "evolution" and talk instead of what we actually think is going to happen.
Hanson/Bostrom etc. talk about the fact that humanity will be able to quickly and significantly change what we are, as in rewriting our genetic code, rewriting our software, and so on. (If you want to call this "part of evolution", that's fair, but beside the point I'm making).
They consider this a "rise" in terms of what we, right now, consider to be better or worse. If you'd tell me that in 10 years, humanity will be replaced by cockroaches, you're right that it doesn't matter to "evolution", but it is certainly something that I, as a human, consider to be a step down.
In similar ways, rewriting our genetic code or making other changes to humanity can be considered an advancement from humanity's point of view.
That's the kinds of things they are talking about, and the reason they use phrases like "steps up the ladder".
> You are very wrong in terms of both their message, and their purposes.
They repeatedly refer to evolution's goals, but evolution has no goals. They are wrong, and I am citing the standard scientific references to evolutionary theory.
Quote: "One important mechanism of evolution, natural selection, does result in the evolution of improved abilities to survive and reproduce; however, this does not mean that evolution is progressive"
The above flatly contradicts your sources, who argue that their version of evolution is progressive.
> In fact, considering they're both respected professors ...
While trying to engage in scientific debate, avoid this common logical error:
> They consider this a "rise" in terms of what we, right now, consider to be better or worse.
But that's wrong -- we cannot possibly know what nature has in store for us in the future. And no evolutionary process, natural or unnatural, can or should be described as a "rise". When applied to human beings, this smacks of eugenics, of engineering the "defects" out of people. It assumes that we understand nature better than we do, or that we can outwit nature, or that we can implement eugenic projects without destroying society. We keep proving that we can't do that.
> In similar ways, rewriting our genetic code or making other changes to humanity can be considered an advancement from humanity's point of view.
So it is a eugenic proposal. All the worse for us. Eugenics suffers from many serious defects, one being that we can't outwit nature, another being that implementing eugenic plans inevitably falls apart for practical and political reasons.
Relating it to evolution is simply a way to give it a pseudoscientific gloss and put a respectable patina on a dangerous social idea.
"They repeatedly refer to evolution's goals, but evolution has no goals."
They're speaking metaphorically.
"The above flatly contradicts your sources, who argue that their version of evolution is progressive."
Like where? Where do they specifically say that?
"While trying to engage in scientific debate, avoid this common logical error:"
I wasn't arguing from authority. I did not say "they are authorities, believe what they say". I said that, since they are respected professors, you might want to give them the benefit of the doubt. Do you really believe that there is no chance that you are wrong and that you are misunderstanding them, and if the fact that they are both respected professors has zero relevance on whether you should at least try to see whether you might have misjudged them?
"But that's wrong -- we cannot possibly know what nature has in store for us in the future"
I'm just pointing out that you are now yourself talking as if "nature" had goals and purposes, exactly the behaviour you found troubling in their writings.
As for the rest of your post, I can't say I disagree with the facts, only with your opinions. Yes, we are discussing here things like changing people's genes, and yes, that means it is eugenics. No, I don't think this is necessarily a bad thing.
More importantly to Bostrom's point, it doesn't matter what we think - people will start doing things like this in the (near?) future, we'd better be prepared for it.
>> "They repeatedly refer to evolution's goals, but evolution has no goals."
> They're speaking metaphorically.
Metaphorically, evolution has no goals.
>> "The above flatly contradicts your sources, who argue that their version of evolution is progressive."
> Like where? Where do they specifically say that?
Read the thread, including another poster's representation of their views: "When Bostrom and others talk about humanity, they usually mean humanity and its extremely advanced descendants." This clearly represents a distillation of their philosophy.
Quote: "How far have we come, and how far might we go? Imagine this progress as climbing a ladder on the side of a tall building, where at each new floor we get ten times more capable."
Hey, it's the topic under discussion, introduced by another poster. It's New Age nonsense with no connection to reality or evolution.
> As for the rest of your post, I can't say I disagree with the facts, only with your opinions.
I didn't post any opinions -- this is a discussion of evolution, one you started. Evolution doesn't rely on opinions, it relies on evidence.
> ... the fact that they are both respected professors has zero relevance ...
Do you never discuss science with anyone, anywhere, ever? You just repeated another poster's earlier logical error. In science, authority counts for nothing -- evidence is the only issue. The greatest amount of scientific eminence is trumped by the smallest amount of scientific evidence.
> Yes, we are discussing here things like changing people's genes, and yes, that means it is eugenics. No, I don't think this is necessarily a bad thing.
Then you haven't studied history or learned any of its most important lessons. A social discussion of genetic engineering of the human genotype based on microbiology, inevitably becomes a social discussion of genetic engineering based on killing all the "inferior" individuals.
Quote: "Throughout its recent history, eugenics has remained a controversial concept.[10] As a social movement, eugenics reached its greatest popularity in the early decades of the 20th century. At this point in time, eugenics was practiced around the world and was promoted by governments, and influential individuals and institutions. Many countries enacted[11] various eugenics policies and programmes, including: genetic screening, birth control, promoting differential birth rates, marriage restrictions, segregation (both racial segregation and segregation of the mentally ill from the rest of the population), compulsory sterilization, forced abortions or forced pregnancies, and genocide. Most of these policies were later regarded as coercive or restrictive, and now few jurisdictions implement policies that are explicitly labelled as eugenic or unequivocally eugenic in substance."
I don't have time to address everything you've laid out here, but I must say that you seem to almost willfully misinterpret my statements. Moreover, many of your rebuttals are simply incorrect on matters of fact.
Please, in the future, try to remember the principle of charity. Also, you might foster more productive discussions by sprinkling a little tact onto your comments.
> Moreover, many of your rebuttals are simply incorrect on matters of fact.
You're wrong, but post your evidence -- let the evidence decide. The authors you cite make a number of obviously false claims about evolution, claims falsified by citation in the standard references.
>>Evolution is not a plan with a goal, it is a blind algorithm that chooses survivors, regardless of the survivors' traits, with the single requirement that they are the fittest for the environment in which they find themselves.
Well that does sound like a goal driven algorithm to me. Except that you can't actually say if a move made by the algorithm will actually produce a acceptable outcome to the algorithm itself. Due to the sheer number of variables, the only option the algorithm has is to do a kind of A/B testing. To make changes to a smaller subset of subjects and see if they survive, if they do they do. If they don't, well then you can kill that test and move on more modifications.
Evolution is an optimization algorithm, which makes changes, tests and makes more changes/corrects based on feed back.
>> Evolution is not a plan with a goal, it is a blind algorithm that chooses survivors, regardless of the survivors' traits, with the single requirement that they are the fittest for the environment in which they find themselves.
> Well that does sound like a goal driven algorithm to me.
Not in the way most people mean. When people hear there's a scheme to evolution, many assume this means a gradual ascent in complexity or intelligence, but that's not necessarily so. There's no relationship between natural selection and any specific endpoint.
> Evolution is an optimization algorithm ...
No, it's an adaptation algorithm. Its outcome are never optimal, only the best approximate response to environmental changes, in an ever-changing environment.
1) That's not entirely true. Evolution is an optimization process and tends to produce more fit individuals over time. Intelligence is a great example of a trait that improved over time because of evolution.
2) No one is claiming that in the first place. The quote is about the evolution of culture and technology, not biological evolution.
This is an interesting issue. At what point will our descendants feel that they are different enough from us through natural or guided (by science) evolution?
> At what point will our descendants feel that they are different enough from us through natural or guided (by science) evolution?
Easily answered: our species has existed for about 200,000 years. Based on that, and barring any speed-up in the rate of evolution by selection (natural or unnatural), we will have been replaced by another species in another 200,000 years. This will happen no matter what else happens -- assuming we're not subject to any global catastrophe, but simply evolve as a species into something we cannot presently imagine.
Even then it would probably not end our species. Even if every country had nuclear weapons and simultaneously vaporized every square inch of land surface (very unlikely), there would be a few carnival cruises and people who escaped to underground bunkers to hold out for enough years to repopulate some place later. It would be 99% losses, but the tough ones would survive. It may take a few thousand years to get back to where we were, but the buried technology would be found, and we would quickly get back to this point, with a lot more genetic resistance to the radiation fallout.
> Even then it would probably not end our species. Even if every country had nuclear weapons and simultaneously vaporized every square inch of land surface (very unlikely), there would be a few carnival cruises and people who escaped to underground bunkers to hold out for enough years to repopulate some place later.
This is very, very likely, and there's even concrete evidence, based on the fact that the human race was nearly wiped out 70,000 years ago, but recovered.
70,000 years ago a huge volcanic eruption with global consequences called the "Toba event" reduced the human population to somewhere between 3,000 - 10,000 people. We know this by analysis of our DNA, which carries a lot of information that can be used to assess our genetic history. That record shows that a severe genetic bottleneck took place 70,000 years ago, and geographic evidence shows a corresponding massive volcanic event thought to be responsible. More here:
The theory behind the Toba event is really interesting, and the wikipedia article does mention that a number of other species are implicated with similar apparent bottlenecks, but it seems curious that this event wouldn't have affected all living creatures universally.
Based on the description of the event, a 5-10 year volcanic winter, I'm trying to imagine how such a disaster might compare to the dinosaur's extinction scenario. Why would only some creatures suffer more devastating effects than others? Does this point to additional complexities in the chain of subsequent events in the post-eruption environment, such as species-specific plagues, and partitioned food-web collapses due to the loss of a keystone species?
Would plants and aquatic species expess such a bottleneck differently, when compared to primates and other apex predators?
> ... but it seems curious that this event wouldn't have affected all living creatures universally.
That's easy to explain based on the fact that some species tolerate temperature change better than others. Remember that the Toba event took place just as an Ice Age was beginning, so there were multiple stressors, affecting many species. The survivors were those that (a) could take shelter against the sudden cold, and/or (b) were naturally more resistant to the cold.
A similar partition happened during the asteroid-initiated dinosaur extinction event 65 million years ago -- some species were better able to deal with the sudden cooling of the global climate. Like the little mammals, who could take shelter underground, and from which we eventually sprang.
> Would plants and aquatic species expess such a bottleneck differently ...
Yes. Some of them are able to tolerate freezing conditions that would kill most land animals. As just one example, there are species of frog that can freeze solid, then recover when things thaw out.
Unlikely to kill every human on the planet, though, but to destroy the civilization, yes, and to make us go back in time in terms of scientific progress/knowledge etc... yes. In other words, it would make it way harder for humans to survive in the long run.
I blame the economists. They had to drop out of their math degree because they couldn't understand exponential functions... surprise surprise now we have earth-destruction level superpowers trying desperately to keep up an economy based on unsustainable exponential growth.
For a much deeper treatment of this subject, I recommend Global Catastrophic Risks, edited by Nick Bostrom and Milan Ćirković. The overarching point is straightforward (see the paragraph above), but the details of each threat are interesting on their own.
1. http://www.amazon.com/Global-Catastrophic-Risks-Nick-Bostrom...