A group of biosphere conservation activists from a type three civilization come across the earth. Using their technology and observations, they see that throughout human history , humans have blatantly disregarded the well being of their fellow multi-cellular life forms , and due to this , they are leading their biosphere down a path of self destruction. they are outraged and greatly desire to safe the biosphere , but due to intergalactic bylaws , they are not allowed to

A) Directly interact with any civilizations below type 1

B) Disrupt the natural ecology of any planet or Moon that they are not native to

C) Land any Individual or Craft on th any planet or Moons whose inhabitants have not reached Type 2

D) Tamper with the orbits of any bodies in a solar system that contains lifeforms below type 2

The violation of one or more of these laws could result in anything from planet arrest ( where the perpetrator(s) may not leave the planetary system of their home world ) for 150 years , to digital purgatory ( where their consciousness is uploaded to a matrioshka brain to survive as primeval sapiens until the heat death of the universe ).

My question is: what is the least Impactful thing that could be done to wipe out the human race without disrupting the natural world?

  • Note:All "type" figures are in terms of the kardashev scale of civilizations
  • 3
    $\begingroup$ What do you mean by wipe out? A complete extinction of ALL people or would 99.999% with a few stragglers be okay? Also, do the aliens delineate the type of human society? Are hunter-gatherers better than subsistence farmers than civilizations? $\endgroup$ – Plinth May 25 '16 at 2:48
  • $\begingroup$ @Plinth All people must be killed in order not to alow survivors to go down the same parth as their deceased counterparts $\endgroup$ – user15036 May 25 '16 at 5:38
  • $\begingroup$ I don't think I can substantiate a full answer but I'm guessing your best bet is going to be some sort of engineered disease. It's difficult to conceive of anything else that won't take a huge chunk of the biosphere with it. $\endgroup$ – ApproachingDarknessFish May 25 '16 at 6:48
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    $\begingroup$ Humans are part of the biosphere. I feel that wiping humanity out would violate rule B. $\endgroup$ – AmiralPatate May 25 '16 at 7:55
  • $\begingroup$ @AmiralPatate The key word of rule B is "Natural" , once a species has removed its self from the food chain , it excludes It's self from being "natural" $\endgroup$ – user15036 May 25 '16 at 12:10

10 Answers 10


Cause geomagnetic storm

Last really bad storm of this type in year 1921 caused telegraphs to go out of the service.

Your rules forbid playing with a planet , whereas the Sun is a star (obviously). So it should be safe to play a little bit with Sun and cause it to produce huge geomagnetic storm which will cause massive electric blackout on whole Earth

I know it does not wipe all the humans. But I think that it will result in era of Dark Ages, where lot of humans will die in unrest and wars.

Also, when you "rinse and repeat" the process, you can put humans effectively back to medieval settings. They will still cause harm to the nature, but I think that given the rules this is pretty good solution.

Alternative: How strongly are the rules enforced?

There are fines for messing with low level species. I get it. But there are also fines for speeding in most countries on Earth. And we all know that in certain parts of roads in certain parts of a day you can go well over the limit without getting caught.

Last time I asked about aliens being limited by some rules I got also answer: Screw the rules and go for it!

But that depends on your setup. How often do you get caught for messing with the planet? What is the probability that police ship is hiding behind dark side of Moon and waiting for you to get caught up in the moment and push the pedal to the metal?

And how much are the aliens willing to break the rules? If they are willing to go for it, then go for nuke from the orbit* and claim solar flare did it

* This advice is just figure of speech. I strongly recommend you to follow intergalactic rules and not mess with humans at all. Should you break the laws, I hold no responsibility for advicing you that. Anyway if you do so, send pics!


Supervirus Kardashev Type III civilizations would likely have mastered completely genetic engineering and possibly even removing biological matter from their bodies entirely. To genetically engineer a plague that would look for specific markers in the host, identifying targets to be human and killing them off before self-destructing wouldn't necessarily be out of the realms of possibility for them.

Ignore the rules Civilization so advanced it's colonizing the galaxy would likely be advanced enough to simply wipe humanity out by tampering with our nuclear arsenal. Sure, it would wipe out a significant portion of the flora and fauna alongside with human, but at the stage this alien race is at, a few millenia won't matter, and the earth will eventually heal without humans to poison it. Should someone come asking, they can just claim to have only just arrived, a bit too late that these silly little chimps just nuked themselves out of existence.

Nevertheless it would still disrupt the native ecological systems. Mankind is a part of it, regardless of the destruction we cause. The rules if followed to the T prevent pretty much any interference until the species read Type I level of technology.

  • $\begingroup$ The trick with the supervirus is to program it in such a way that it will first infect the entire population without being recognized as a mortal danger. Think something on the range of a flue. Only after virtually the entire population is infected, the virus may get down it's actual business, when it's too late to save lives by means of quarantine. $\endgroup$ – cmaster Nov 24 '18 at 23:52

If they can't directly interact with humans, or affect the biosphere, then I think that leaves them with one general solution:

Just show up, and let the humans to wipe themselves out.

One way of doing this would be just to make their aircraft visible to the humans. Done at the right time and place, this could be devastating.

For instance, if highly advanced vessels appeared over hidden Soviet military sights at the height of the Cold War, the USSR would assume the craft belonged to the US, and might be provoked to attack.

The ensuing nuclear exchange would severely set back humanity, if not wiping them out entirely, and the Earth's ecosystem would likely recover in time.

Since they aren't communicating with the humans in any way, then they can argue that they aren't actually "interacting" with them.

  • $\begingroup$ Nice approach. Unfortunately it requires some extensive knowledge of human politics to pull this off. And it requires acting at the right time, you just don't have a Cuba crisis on the edge all the time... $\endgroup$ – cmaster Nov 24 '18 at 23:55

Multiple answers have mentioned viruses--but there is the problem that there's nothing that will give a 100% kill. However, look at what happened to the New World--multiple diseases. Immunity to one doesn't mean you're immune to another.

Infecting everyone first isn't actually an absolute requirement as you can have an airborne disease and keep raining it down.

However, if you want to infect everyone first the answer is simple--something that spreads rapidly but has a long incubation period. Nothing like that exists at present but what if you combine two existing diseases? Lets hop back to 1980, the evil aliens tack the HIV code onto the influenza bug, make a few antigen changes so nobody resists it. Hit all the major cities of the world (make fake meteors that protect it through the fire, then break up.) People get the flu, they get better, after a while their immune system starts to break down. It will hit too fast for the researchers to find a solution. (And the fact that just about everyone is infected will make it much harder to pin down the problem.)

This won't be a complete kill, though--something under 1% of the population is immune. However, do the same thing with the cancer-causing versions of the HPV virus. While I'm not aware of any immunity there there probably are some--but it's not the same people as were immune to HIV. Those are the two slow viruses I'm aware of but I'm sure there are more. The aliens use as many as they can.


I suggest you read James Tiptree, Jr's classic "The Screwfly Solution". Aliens seed the atmosphere with a substance which cross-links the (already cross-linked) sexual and aggressive drives, causing the men to kill off all the women. A very good story, but really depressing.


Autoreplicating nanobots, replicating on strictly human cells --- with a DNA check that should be simple for a type III civilization. Like a supervirus, but more specific. The nanobots can die and auto-destroy to basic component after a while... you can spread them in the atmosphere to get started.

(Idea from Hugh Howley "wool" sequence)


The simplest solution:

Step back and wait it out. At current rate of destruction it's just a matter of time. The planet has a way of recovering from mass extinction events, it'll all be back in some way, shape or form within a million years or so. Maybe in due course intelligent life will once again arise from the ashes.

Electronic interference

Your rules don't exclude remotely interfering with our technology, something we'd be particularly vulnerable to just at the moment. Faking a couple of missile launch signatures onto the great power's tracking systems should do the job fairly quickly.


Does "interacting with civilisation" include (a) interacting with individuals in it, or (b) affecting individuals without "interacting" with them?

Level 3 implies some extremely high level technical abilities, including changes specific to the immediate environment around each person. Perhaps distortion of electromagnetism - light we see, electrical impulses from our senses or in our neurology. Changes to the immediate environment of each person - changing the partial gas pressures to prevent respiration would be a neat one. So would transforming all food at the point of eating to remove key nutrients as they are ingested. Doing this for a few billion people over a few years (if not all at the same time) wouldn't be much of a challenge.

I'm reminded of a SciFi comment whose source I cannot remember, that to prevent the rise of Hitler, all that would have been needed would to create sound waves of voices next to his ears, day and night, preventing concentration and disrupting purposeful behaviour, and consigning him fairly quickly to an asylum, suicide, or to behaviour that gets him ignored rather than followed.

There are probably thousands of ways your aliens could do something similar to the environment people live in. Modify sperm cells before conception (not strictly "part" of a person), create distortions to vision calculated to cause fatal accidents, transform nutrients, transform the immediate atmosphere, tamper with human knowledge and communication to create harm directly or chaos, or to insert false harmful information into human knowledge, just name it. Imagination is the limit.


You can obtain a large amount of DNA sample from the desired organism and analyze it.

Then you could manufacture a technology that scans a certain amount of land searching for and identifying the DNA.

After it identifies the DNA the technology will kill the organism off by releasing bugs that make it sick.

If you want a catch then the device could be faulty: it doesn't identify all the population, just about 80%. Think of it like a missile that tracks it's target.

After several scans the organism is extinct, another technology will proceed to remove the trace of the organism, buildings, farms, deforestation, etc.

  • $\begingroup$ Tracking down the DNA of a single organism will maybe help to isolate that only organism. Else any human could be found guilty in trials based on DNA evidence. $\endgroup$ – L.Dutch Nov 25 '18 at 4:42

A highly contagious (likely water and airborne, and not temperature sensitive) viral illness that prevents reproduction would slowly kill off the entire human race without touching any other organisms -- assuming it doesn't jump the species barrier. If this isn't fast enough, then a virus that attacks the telomeres in the DNA. From my understanding, this would accelerate the aging process sufficiently that youth would die quickly before reproducing, and adults would die off quicker.

Recall that the influenza virus has, on a couple of occasions, wiped out substantial fractions of the human race. And SARS (a coronavirus) scared more than a few people as well.

One could also invoke prion diseases, or similar phenomena.

If you use a disease, it would likely have to be something completely unlike anything humans have seen before, otherwise there is likely to be some cross-immunity. It would have to be highly virulent, highly transmissible, and highly contagious. I would think that it should have a long period of shedding before symptoms show up, otherwise people die before they can transmit the disease. It should have at least one, ideally multiple non-human reservoirs (fruit bats are good for this as they go almost everywhere; I wonder if cockroaches or ants could act as a secondary reservoir?)

If you don't want to go the disease route, then consider technology. Nanotech could easily be designed to target unique segments of the human nervous system and/or brain. And a rogue AI could, given the pervasiveness of online connections, likely wipe out most of humanity.

Or, like has been said in other comments, simply wait. Humanity is fairly likely to wipe itself out, given sufficient time.

EDIT (2019/01/04) - there is an interesting podcast that addresses the concept of existential risk for mankind (though necessarily superficial due to time constraints) - it's called The End of the World by Josh Clark. It may be worth taking a listen

  • $\begingroup$ There's a big difference between the major epidemics we've seen, which wiped out quite a large fraction of the population, and an extinction level epidemic: Even if you wipe out 99 humans out of 100, the remaining will just start over. To get to extinction level, the remaining humans must be so few and far between that it's virtually impossible to find mates and raise children, the average survivor must be able to spend a lifetime wandering the planet and finding nobody. No epidemic has ever come close to this. $\endgroup$ – cmaster Nov 25 '18 at 0:01
  • $\begingroup$ I totally agree - that was what I was alluding to when I said that it would have to be unlike anything humans have seen before. The Spanish Flu affected about 30% of the worlds population, but "only" had about a 20% mortality rate. The plague and tuberculosis have also taken large numbers of people, but over an extended period of time. Polio and malaria have also killed large numbers of people, but again, over long periods of time. As you say, no epidemic has ever come close to extinction level. Having said that, we are rapidly approaching the post-antibiotic era, so perhaps things will change $\endgroup$ – Doc C Nov 26 '18 at 17:11

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