# Epidemic friendly time traveller

My time traveller from the distant future is about to get stranded back in time, but realises that by travelling back a short time, maybe 100000 years, he is going to leave a trail of destruction by introducing a swathe of advanced diseases among the local populations.

He figures that all he has to do is travel back further: to a point where the proteins and receptors his viruses need haven't been evolved yet. However, he still wants to be able to interact with the inhabitants, so he wants to travel back as little as possible in the hopes of having someone/something sapient to talk to.

How far does he go?

• 100000 years ago he isn't going to find anyone to talk to that he could actually understand, and they'd probably kill him on sight anyway. But in any case they would be hunter gatherers in small groups, he's nopt going to start a huge epidemic. People just didn't travel that much outside their group. Not safe. Mar 13 '20 at 12:19
• Then you need to be within the last 10000 years, before agriculture is no use to him Mar 13 '20 at 12:54
• oh I get you now...well since we have no idea what the medical tech is like, I suggest he wear a full body condom Mar 13 '20 at 12:58
• "Handwave that (a la Dr. Who)" and science-based are not compatible. Mar 13 '20 at 13:30
• Also, lots of viruses will be wandering around in the past that have not made it to the traveler's day. So he wants the full-body-condom for himself. From his point of view, small pox has been extinct for centuries, just as an example. Mar 13 '20 at 13:32

Human viruses in certain cases can infect animals (transmission from animals to humans are the ways the novel coronavirus and HIV epidemics emerged) and even amoebas. So if you want your time traveller not to infect anybody with his own parasites, he should travel to the times before unicont cells emerged (I do not know human viruses that infect plants).

Yet, there is still high probability that besides human viruses he also would carry bacteria and viruses infecting bacteria. Many bacteria can survive on their own without a host.

• I acknowledge Zoonosis is a risk, but it is rare enough to be unlikely to happen to a given individual?
– pjp
Mar 13 '20 at 13:23
• @pjp This depends on what risk your traveler is willing to accept. This is not a rare occurrence and viruses are very prone to mutations. What prevents the transmission between species is mostly their immune systems rather than incompatibility of the viruses with the hosts. It is possible to conceive that prehistoric animals could have weaker or totally different immune system, incapable of combatting the modern diseases. Mar 13 '20 at 13:28
• @pjp it is also possible, the traveler would be unsafe contacting the prehistoric animals. Mar 13 '20 at 13:30
• @pjp The only way to make your traveler totally safe biologically-wise, is to completely sterilyze his body of any species other than human. But this would render him quite sick because certain bacteria living in the guts are needed for food consumption. Mar 13 '20 at 13:44
• @pjp bacterias living in the gut go out each time the traveller poops and many of them can continue to live in the soil. It is unpredictable what consequences this can bring if some animals will eat them. It can go unnoticed or it may make the animal sick. Anyway, it introduces new species to the prehistoric world which weren't there before. Mar 13 '20 at 13:51

a point where the proteins and receptors his viruses need haven't been evolved yet

Without any specific information on the receptor the virus is using, the safest bet is, dealing with a virus infecting homo sapiens, to travel to a moment in time when homo sapiens is not yet present on the planet.

so he wants to travel back as little as possible in the hopes of having someone/something sapient to talk to.

Well, if homo sapiens is not yet evolved, there are no sapiens around to interact with.

Another good reason to follow the recommendation to stay inside and not move from home, neither in space nor in time!

• Well, if homo sapiens is not yet evolved, there are no sapiens around to interact with. Given that sapiens in the context is a misnomer, the same apply after homo sapiens evolved Mar 13 '20 at 11:40
• I used sapient, not sapien, meaning "having wisdom". The homo sapien-sapien-sapien-etc. traveler from n-million years in the future doesn't want to have to go back to the permian era to play cards with turtles.
– pjp
Mar 13 '20 at 11:46
• @pjp yes, I know what sapiens means. I'm just having difficulty to recognize any wisdom in the homo species, no matter how obstinate the repetition of sapiens. As for 'sapient', the etymology is the same, it's a matter of a minor nuance (sapient - being/acting wise, sapiens - possessing wisdom) Mar 13 '20 at 13:00
• @AdrianColomitchi, to quote Calvin&Hobbes, the proof that there is intelligent life in the universe is that nobody ever contacted us
– L.Dutch
Mar 13 '20 at 13:18
• @AdrianColomitchi It was kind of a reply to the answer as well since it's really missing the point of the question: It's not insisting that the traveller or the locals are modern homo sapiens and seems to infer sapient = homo sapiens, despite as you note, the poor correlation. There's also no instant at which creatures stop being one species and become another, mutually immune from each others diseases, its a gradual process. I'm interested in what the time-frame for this would be.
– pjp
Mar 13 '20 at 13:21

The best option would be to sidestep the whole issue of time and wear a coverall suit with helmet, like a spacesuit.

The time wouldn't be a problem then and he could expose individuals to himself on a more clinical level and see if they get sick and die, rather than expose multiple people at once to his dreadful diseases.

• So the time traveler is going to imprison people in quarantine and observe how they react when he infects them? The whole point of an epidemic is that it spreads, so if you infect anyone, you had better isolate them or risk infecting everyone else. Mar 13 '20 at 13:17
• @NuclearWang yep, but not 'when' he infects them... 'if' he infects them Mar 13 '20 at 13:18
• If you're infecting people by accident, then you clearly do not have the ability to create an effective quarantine (you can't even prevent transmission from yourself to others, much less between others). A prerequisite of a quarantine is knowing who is infected - if you're isolating only the people who are obviously sick, it's too late. Mar 13 '20 at 13:23
• where did I say by accident? He'd do it on purpose in terms of an experiment, until he opens his suit/helmet there is no danger of infecting anyone. Obviously he'd sort out a quarantine first Mar 13 '20 at 13:23
• I read "if he infects them" as an unplanned incident. I don't understand, is the time traveler going to deliberately infect others or not? Mar 13 '20 at 13:25