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Verging on the realm of science fiction, my question is that is there any theoretically possible way, biologically/chemically, with which the entire human race can be killed without affecting the rest of the biosphere at all? I am only curious about theoretically possible no matter how unlikely. If we encounter a sufficiently advanced alien civilization bent on our destruction, would it be possible for them to make sure all humans die without harming any other living organism on our planet?

Is there anything biological/chemical which makes us unique or different than other lifeforms on Earth? Something which can be used against us? Or are we just so similar with a bunch of other species that we cannot be wiped out without other lifeforms getting harmed or our destruction cannot be ensured? Is it possible to artificially make humans extinct?

Thanks you.

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Does it have to be an external mechanism? (i.e. not human-caused) –  Brandon Invergo Jul 23 '13 at 12:17
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This question appears to be off-topic because it is not about biology as defined in the FAQ. It would be much better suited to scifi.stackexchange.com –  MattDMo Jul 23 '13 at 16:00
    
@BrandonInvergo Actually I would be okay with either one. I prefer an external mechanism but just for the sake of intellectual curiosity, internal mechanisms will also be interesting. –  Fixed Point Jul 23 '13 at 20:24
    
@MattDMo I though about this very carefully and decided to put the question here instead of at scifi.stackexchange.com because I am looking for scientifically theoretically possible methods. This is specifically related to human biology and I don't think scifi.stackexchange.com is the proper place to ask bio questions. This is a "question about biological concept". Is there anything biologically different about us which makes us different enough from other species on this planet? –  Fixed Point Jul 23 '13 at 20:28
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I think it's a fine question. It's a bit abstract and probably impossible to answer conclusively, but it's grounded in actual biology (immunology, etc.). I think such hypothetical questions are fine as long as nothing gets too speculative so as to no longer be based on modern scientific knowledge. –  Brandon Invergo Jul 24 '13 at 7:18

3 Answers 3

up vote 3 down vote accepted

Infectious diseases is probably the only way I can think of. Viruses for example may have tropisms based on receptors to which they attach. These receptors may be and often are unique to a species, and thus an infection could target humans very specifically. Differences between humans and animals present the weaknesses and resistances we would have to such an infection. As an international species, spread of the disease can be quite rapid. However, our increased intelligence means we could given time, understand the threat and combat it.

If an infectious disease killed rapidly enough that development of a cure or administration of one was not easily possible, the disease itself would be wiped out by quarantine measures (theoretically). For an infection it is not wise to kill the host too quickly as this prevents survival of the infection which is dependent on its host.

Thus we want an infection that is non-pathological at first then rapidly pathological but affected the whole world as a whole. This infection would need to spread to every individual so would have to be incredibly infectious and for no individuals to have any resistance to it and also ideally to kill everyone at roughly the same time or at least quickly enough to prevent us having time to come up with a cure. The only way I can think of that would fulfil all of those conditions is if the infection on it's own was non-pathological but then a novel secondary universal factor made this infection pathological. This factor would have to be in low levels prior to infection but then rapidly escalate to worldwide distribution.

Disclaimer: Obviously this is theoretical and probably not at all possible.

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Apart from not being extremely infectious, HIV/AIDS had some appropriate characteristics: long incubation period and initial deaths being attributed to diseases taking advantage of a weakened immune system (initially predominantly affecting people that could be marginalized--at least in the U.S.--might also have made the disease more effective). If initial symptoms appeared among the poor (no health care, somewhat marginalized), a disease might be undiscovered and later mostly ignored until it is too late (but a trigger factor would seem more effective). –  Paul A. Clayton Jul 24 '13 at 15:14
    
Thanks, +1 and accepted. A virus specifically engineered is the only way I could think of as well but wasn't sure. I was thinking of something which would lay dormant for a long time to make sure everyone is infected and then all of a sudden become active and just wipe out everyone very fast. Not sure if this is even theoretically possible or not. –  Fixed Point Jul 25 '13 at 21:12

Trick question. By driving humans to extinction, you almost certainly will be driving all human-specific parasites and pathogens to extinction as well.

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Such would probably also tend to reduce populations of some animals such as cockroaches and raccoons which exploit human-created niches better than other animals. –  Paul A. Clayton Jul 24 '13 at 15:00
    
Wow, good answer. I didn't think of this at all. I wish I could accept both answers. +1 anyway. Thanks. –  Fixed Point Jul 25 '13 at 21:06

This answer is building on the answer by @BrandonInvergo and focusing on the "..possible way...the entire human race can be killed without affecting the rest of the biosphere..." part of your question.

No, it is impossible to remove humans without affecting the biosphere (barring some extremely made-up scifi scenario) because many species are adapted to us. It doesn't stop with the parasites and pathogens in Brandon's answer. Most obviously, the majority of all domesticated animals and plants will go extinct, and these number ~750 species (Duarte et al 2007). A large number of other species (e.g. plants, insects, birds) are also adapted to man-made environments and many are likely to go extinct if humans disappear, and these effects will cascade into their respective ecosystems. Just look at what is happening to species adapted to traditional low-intensive pasturelands in e.g. Europe.

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Really? All of those species would go extinct as well? Wouldn't they all just adapt back, meaning adapt to live without man-made environments? That's how they were living before. –  Fixed Point Jul 31 '13 at 22:36
    
@FixedPoint For domesticated species most will go extinct since they have been so heavily modified and cannot compete successfully in the wild. For other species dependent on man-made environments the outcome depends on how rapidly their living environment changes, but many are likely to go extinct. Some are likely to find refuge in their native habitats, e.g. natural grasslands. However, the original habitats are sometimes lost or the species is extinct from their original range, and some have evolved adaptations to their current antropogenic environments. –  fileunderwater Aug 1 '13 at 9:25

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