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I want to create a world where tying yourself to a single partner would be considered irresponsible because it is potentially deadly. The more often two people come together and exchange DNA through kissing etc, the more likely for them to develop illnesses due to repeated contact with each others DNA. Naturally, the people would be either more social or more introverted. This would be because you either want to limit exposure to other people completely or you wish to have more variety in your life, thus lowering your risks overall. Contact could be limited by increased layers of clothing and more vigorous cleaning regimes, but I'm not sure how the biology would work.

Another risk is that repeated exposure to the DNA of another person could be used as a weapon - say a disgruntled ex repeatedly exposing their partner to their DNA to cause them to develop diseases and die. Also, if two people wanted to have a baby together specifically, how would they do so without risking either person's life if they are initially unsuccessful. Furthermore, if they are successful, how could I plausibly explain some form of resistance between parent and child to prevent children from being passed around or rotated through families to prevent people from becoming sick. After all, babies often drool, spreading their DNA rather effectively all over whatever they come into contact with.

What would be a way to make this repeated exposure dangerous without using too much handwavium and how would resistance to children/parents be explained.

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    $\begingroup$ you are literally covered in foreign DNA, our skin and digestive system are covered in bacteria, mites and other micro organisms, if they can't tolerate foreign DNA then they won't live through childhood. $\endgroup$ – John Jul 8 '17 at 23:15
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    $\begingroup$ @John it's not all foreign DNA, I specified that it's from other people not all other foreign DNA. You can cuddle your cat as much as you like for many years. $\endgroup$ – Gladiator Kittens Jul 8 '17 at 23:16
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    $\begingroup$ That makes even less sense, DNA is DNA, unless your humans DNA is somehow infections it will make no difference the source. $\endgroup$ – John Jul 8 '17 at 23:21
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    $\begingroup$ @John Evidently I am not a biologist, hence the question on how to make it believable $\endgroup$ – Gladiator Kittens Jul 8 '17 at 23:22
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    $\begingroup$ You can't with DNA but you could with some other human product, Major Histocompatability Complex would fit the bill, it varies from person to person due to genetics but it is the products people interact with.we know humans can detect the MHC of others due to these products. A persons sweat, hair, and sloughed skin contain it so story wise it should play out very similarly. $\endgroup$ – John Jul 8 '17 at 23:31
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If this is the case, then everyone's genetic code is going to be extremely unstable, and unrecognizable over time.

Further, at this level of instability, it would not be limited to your species either.

This means that what--you are what you eat?

For a higher organism to survive and thrive with this sort instability is strange indeed.

Here's some info on GMOs, and this phenomenon.

In it they say:

It is clear that higher organisms have developed robust mechanisms to prevent foreign DNA from routinely invading the genome.

Biologically, foreign DNA is the enemy. It's only in the specific case of reproduction, with sperm invading the uterus that it is allowed. Even then, the female body does kill off many of them. And in some cases, the fetus is aborted because the body mistakes it as a parasite or foreign entity.

In other words, humans and most animals have an intricate "security system," that can sometimes even be too vigorous when it comes to reproduction.

Bacteria can have gene transfer, but that's over generations, generally.

But you might want to look at this article on telegony concerning flies:

Working with flies, Angela Crean, a research fellow at the evolution and ecology research center, picked up on her mentor’s work of looking at how male factors can influence offspring outside of the DNA in his semen.

In this case it seems to influence the offspring not the mate, which is different than what you are looking for, and it isn't exactly DNA-based--but it is interesting. The effects of this belief actually support monogamy, so that you bring up children with your genetic traits.

Before you even get to your question, you need to look very closely and research what your premise actually means, and look at analogues that you can find.

Here's an article in PDF form on Microchimerism. While this specifically looks at the exchange between mother and child mostly, it is worth reading.

Your people sound as though they have very very weak immune systems.

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You could have a hyper-active immune system. It considers hostile DNA a threat, essentially you are allergic to other people. Occasional exposure is fine, or a few encounters with one individual. Repeated contact would thus be dangerous as you get a steadily stronger and stronger immune response.

You could explain this by having some really nasty local parasites that are very dangerous. A vigorous and hyper-vigilant immune system to fight off the parasites is more important than being able to repeatedly contact one person.

This would lead to big differences in society, reproductive urges, coupling urges, etc. People would be wired in a way that's compatible with this, so you could for example see them come "on heat", get intense coupling urges, then once that is done lose interest in each other. Babies would need something to help them survive, for example perhaps they share their mother's immune system for the first few years - delivered and updated while nursing.

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It is breezy here, me waving my hands so briskly. This scheme is the opposite of Thursby's, where repeated exposure builds a stronger and stronger immune response. But here goes:

Imagine that each individual's genome is rich with transposons: infectious agents which jump from organism to organism with their load of genetic code, and also jump around within an individual. These transposons carry with the genes and the genes are transcribed and used by the individual. It is not so far from the truth - from wikipedia

Transposable elements make up a large fraction of the genome and are responsible for much of the mass of DNA in a eukaryotic cell. It has been shown that TEs are important in genome function and evolution.[2] In Oxytricha, which has a unique genetic system, these elements play a critical role in development.[3]

I am 99.9% certain that organisms have ways of suppressing transposons, as they can be troublemakers. Loads of mobile transposons would pose problems for the individual, as transposons can jump around within a genome, land in the middle of a gene and so disrupt it, but maybe these organisms have landing sites to call in the transposons and minimize damage.

My own genome has tolerance for my own transposons because they are always jumping from here to there. Anything new is considered foreign and attacked. But repeated exposure to the same transposon might elicit tolerance. The alien transposons (yours!) are allowed in to jump around.

The risk: I incorporate your transposons and your DNA into my genome. Maybe the landing sites for transposons are such that the incoming one ousts whatever was there previously (this might be necessary to prevent gene duplication). Over repeated exposures my genome becomes more and more like yours. I become you.

Is this bad? I do like your red hair. One organism gradually acquiring the genome of a different one would have effects that would depend on the differences between the two organisms and the cells in the organism whose genome changed.

How to work it in a story? Maybe in this future humans are descendants from a time when every fetus was strongly engineered, and different camps of genetic engineers made their works incompatible with each other on purpose for competitive reasons - like VHS and Betamax or Apple and Samsung. Now that time has passed but the genetic legacy remains and one must be careful: mix and match can be unpredictable.

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