Mars colonisation wont save us from extinction

There are a bunch of great articles on WaitButWhy.com about SpaceX and Elon Musk explaining why they are trying to set up a permanent human colony on Mars.

The TLDR is: additional human colonies on other planets will "back up" our "humanity hard-drive" to safeguard us (as a species) from extinction^*.

For the record I'm a huge Elon fan and am 100% in favour of the goal of expanding humans to other planets/habitats, however I wanted to point out that doing so will not in and of itself prevent the extinction of humanity. To understand why we need to think about the likely existential threats to our survival.

Natural Disasters/Rapid Climate Change

This might seem like two things but they are both the same, one is caused by humans and the other by natural forces. This is the one thing that extra-terrestrial colonies will be protected from, and making the colonies in the first place will help us learn how to help survive on the earth. The likelihood of humanity being wiped out by asteroid impact over the long term is extremely high. If for no other reason this is why we should become multi-planetary. It also possible mankind will make itself extinct by causing inhospitable changes to the climate. For a really cool video simulating a 500 km asteroid impact check out this link: Discovery Channel - Large Asteroid Impact Simulation.

Global War / Political Change

Our way of life and accumulated knowledge is actually very vulnerable to war and political upheaval. Many times in the past technical and political advances have been lost due to wars and changes in the political landscape. Knowledge can only survive if it is passed down from generation to generation or if the knowledge if preserved in a way that is accessible to survivors. To hear Carl Sagan talking about this kind of problem you can watch this video: The Frailty of Knowledge Carl Sagan Tribute Series TLDR: Political change can lead to the wholesale destruction of knowledge. A large enough war would also achieve this. Maybe just maybe, extra-terrestrial colonies could protect us against this danger, but probably not (see next paragraph).

Nuclear War

Fictional  post-apocalyptic works (like the Fallout game series) have conditioned us to believe that some humans would survive a nuclear war. This is unfortunately incorrect. It has been calculated that if a nuclear war occurs there will be no human survivors. This is not because no humans would survive the initial blasts, or even that humans couldn't evade the radiation. It is because the change to the climate would be so severe that it would be completely uninhabitable to any mammals or other large creatures. In essence the effect is that this is another flavour of man-made rapid climate change. 

Extra-terrestrial colonies however will not save us here. 

Why? 

Because the other colonies do not exist in a vacuum (OK, so they might physically but not politically). Whatever the causes of the global-nuclear war might be, the actors involved would likely see the other colonies in the same way they do other countries: just additional targets for their warheads. If I were a betting man I'd give good odds on nations already putting into motion the frameworks necessary to neutralise any extra-terrestrial colonies that they consider a threat to their national interest. By the time there is 1,000,000 martians (and probably  much sooner) there will be weapons targeted on their homes capable of their destruction (probably from multiple nations). This may not be nuclear warheads. Extra-terrestrial colonies will be uniquely vulnerable to sabotage.

It is simply impossible to create a vibrant colony that is mixing regularly with earth whilst also maintaining complete political separation.

AI-Maggeddon

When the machines finally realise that humans are standing in their way to the most efficient production of paperclips they will not draw a distinction between Martians, Terrans, or any other colony of humans. If they have the means to bring about the extinction of terrestrial humans they will also have the ability and motive to destroy extra-terrestrial ones too. 

Natural or Artificial Pestilence.

Probably the biggest danger from pestilence comes from human or AI designed weaponised viruses/nano-bacteria however it is also possible that the microbes will eventually win the war they've been waging against us since the dawn of time. In either case having colonies on Mars will not save us here.

Why?

Because in order to thrive financially those colonies will be dependant on the free flow of people and goods to and from earth. Maybe they will get lucky and the pestilence will be discovered in time for them to close off all the ports and deny entry to carriers, but given this is a human race extinction type pathogen, they likely wont and thus they will also be destroyed. In any case solar system based colonies are not a very good safety net for this type of problem.

Possible Solutions

Given that only one of the many likely apocalyptic scenarios is completely avoided by putting people on Mars, what can mankind do?

The above problems boil down to accessibility and inter-connectivity of humans. For a real backup we need humans out of the solar system, and preferably out of communication with earthlings and their AI masters. A good option would be a continuous stream of Arks or Generation ships dispatched into the cosmos in random directions. With no contact with earth it would be difficult for any paperclip obsessed virtual brain, or powerful religious cult to find them and as they have no intention of returning they would not pose much threat either. In time those ships would send out additional ships in different directions exponentially increasing the difficulty of xenophobic actors to find or care about them. In addition, because the ships do not return and have no contact with earth the ability of pathogens to be transmitted to them from earth becomes minimal.

Which is another good reason for going to Mars. The lessons we learn from establishing remote colonies will teach us how to construct and live on generation ships. I only hope there is yet time.

NB: For the purpose of this article the word "extinction" also refers to any event that leaves any remaining humans in a pre-industrial state of technological empowerment.