This is a terrible planet for animals to live on, with all the humans around. Someone should just put all of them down.

There is a group of radical vegans/animal rights activists that want to kill all animals. Specifically:

  • They want to do this with the minimum power and influence possible.
    • You can assume they have any resources, but the less the better.
  • All members of Kingdom Animalia must be dead.
    • The exception to this is humans. They must suffer in a world without animals.
    • Specifically, they want to avoid killing humans, unless it is a consequence of the animals dying. (Shooting people is generally frowned upon. If people die because the bees aren't pollinating fruit, that's fine.)
    • Sterilizing all the animals will mean that they will all be dead eventually, so that is fine too.
    • They prefer killing the animals humanely. Animals getting eaten is absolutely off limits.
    • They don't have to kill them all at once. They can kill all the major animals first, and then start picking off other species one by one.

How can we put these poor creatures out there misery?

(Note: Remember, this is fiction. Although answers should be realistic, I do not plan on doing this in real life.)

  • $\begingroup$ Your activists would have to be markedly shortsighted to accomplish your goals. It is remarkably hard to kill all of the animals without killing humans, as you noted. This implies that they have a sense of "direct causality" that matters to them, but I have found very few individuals agree on what is direct and what is indirect when you really pester them about the corner cases. $\endgroup$ – Cort Ammon Oct 8 '15 at 23:18
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    $\begingroup$ Kind of silly. These activists would all be out of a job if they pulled this off. $\endgroup$ – Oldcat Oct 9 '15 at 0:25
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    $\begingroup$ People will all die off probably before the last non-human animal is dead. So take the short cut and just kill off all the people instead. $\endgroup$ – bowlturner Oct 9 '15 at 14:03
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    $\begingroup$ So like PETA? Only a bit more extreme? $\endgroup$ – Michael Richardson Oct 12 '15 at 20:36
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    $\begingroup$ @Green It makes little sense to begin with anyway. $\endgroup$ – PyRulez Oct 13 '15 at 19:35

7 gallons of botulinum, spilled in the oceans worldwide would theoretically kill every oceanic aerobic life form.

7 liters of botulinum, spilled in the freshwater reserves (rivers) of the world would eventually kill everyone and everything that drinks freshwater or lives in it.

The End

  • $\begingroup$ Wouldn't that also kill the humans? $\endgroup$ – PyRulez Oct 8 '15 at 23:20
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    $\begingroup$ If you announce it after doing it, a lot of humans will die, but the rest will immediately switch to chemically prepared (hydrogen burning) and cleansed water. The life loss would concentrate on animals. $\endgroup$ – Youstay Igo Oct 8 '15 at 23:27
  • $\begingroup$ So, won't this kill all plants, too, thus completely screwing over the entire world? $\endgroup$ – HDE 226868 Oct 8 '15 at 23:59
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    $\begingroup$ No. It won't. Botulinum, thought being outrageously deadly, is a very large compound and as such, does not stay stable for long. By the time ocean water evaporates and river water joins the underground water reserves, it would have naturally disintegrated into harmless things. Plus, I don't think botulinum is harmful for plants too. $\endgroup$ – Youstay Igo Oct 9 '15 at 7:53
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    $\begingroup$ The humans would probably save some of the animals too, by giving them the prepared water. $\endgroup$ – PTm Oct 13 '15 at 13:30

Increase CO2 output, greenhouse gas output and ocean acidification (already happening anyway), then wait for climate change to render the planet uninhabitable. Whilst doing this, invest heavily in research into making Mars habitable. Then just send a rocket to Mars for colonisation with only humans on board. Everything on Earth dies except for humans which now live on Mars. Job done.

This method is probably less psychologically damaging than living on an Earth with no animals and this method also gets rid of the annoying problem that we heavily rely on animals to survive on Earth. (The research would have been designed so that we didn't need any animals on Mars.)

  • $\begingroup$ This will kill of many of the big animals, but will be far from killing off all of the animals. Even some relatively large animals, like livestock, will survive any climate change that happens. $\endgroup$ – ckersch Oct 13 '15 at 19:57

The most tricky thing is to get rid of the animals that are the most like humans, ie. big mammals. After that, it becomes easier to discriminate.

step 1, big mammals

Design a deadly strain of Pertussis that is transferable between species, but is still vulnerable to the standard DTP vaccine. Since most humans will be vacinated, the loss of human life will be negligable, but the animals should go very quickly.

In order to hit as many species, the trick can be repeated with other diseases that most humans are vaccinated for.

step 2, big non-mammals

Since a cross-species virus is plenty challenging, the best we can probably hope for is to get rid of all mammals. Luckily, for anything that is too dissimilar from a human for our cross species virus to work, we can simply tailor a virus to that species or kingdom: if our pertussis won't jump to the lizards, the lizard virus won't jump to the humans either.

step 3, insects

Animals below a certain size (mosquitoes, beetles) will be impossible to eradicate by virus. Luckily, we can use size as a discriminator: we spray the planet with DDT. Sure, this will give most humans cancer, but they'll live. The smaller animals won't be able to metabolize the poison and will die. Just find the maximum level of DDT that can be introduced without immediately killing humans.

After this, anything that's still alive should have its ecosystem so thoroughly disrupted that they will struggle to cope.


The biosphere is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. The biosphere weighs approximately 1.8 exagrams or 1.8e18 grams. Halting the life processes in each of those organisms isn't feasible to do individually. Even area-of-effect weapons such as nukes won't kill anything living a few meters underground or away from ground-zero.

Launch enough nukes to start a nuclear winter. Well prepared humans will survive but if the nuclear winter is deep enough then most plants and animals on Earth's surface will die. After the winter is over, the humans will emerge from their bunkers to a great wasteland, devoid of most plant and animal life.

The same effect can be achieved by throwing a big enough rock at Earth.


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