If you and your significant other traveled back in time 50 years, had a child (who gets citizenship of the fictional country in question due to being born there) and left the child with a trusted caretaker to raise him/her, and then you traveled back to the present, would a DNA maternity test seem to indicate that you are the child of your child? And would your significant other present as a half sister?

Could these test results feasibly convince authorities in this country to grant you both citizenship based on the citizenship of your "parent"? Assuming the laws in this country closely resemble the US and they are unaware of the existence of time travel.

  • $\begingroup$ Is the child left in the past for good? $\endgroup$ – Alexander Apr 9 '18 at 21:20
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    $\begingroup$ If you mean a DNA analysis as is routinely done to establish paternity, it would indicate a close relationship. I don't know how American citizenship law works, but if it's similar to what other countries have then a birth certificate is vastly more important than DNA. DNA testing is used mostly to get child support payments. I don't even have the remotest idea how one would proceed to use DNA testing to establish citizenship. $\endgroup$ – AlexP Apr 9 '18 at 22:03
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    $\begingroup$ @AlexP, as a U.S. citizen with a bit of law experience I can say with confidence that since it doesn't prove where you were born, it has no value for citizenship. But... welcome, Fireprufe15, to worldbuilding.SE. Please visit our tour and help center pages to learn more about us, which is important because this question was right on the line as on-topic, but only because I'm ignoring Stack Exchanges one-question-one-correct-answer model. Please limit future submissions to a single question. $\endgroup$ – JBH Apr 9 '18 at 22:42
  • $\begingroup$ @JBH While I intended for the last paragraph to be the real question, I realize now I could have worded it much better. I'll do better in the future, but I think I'll leave this one as is since it already has good answers. Thanks for the advice and welcoming words. $\endgroup$ – Fireprufe15 Apr 10 '18 at 5:19
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    $\begingroup$ The real question is that if you had access to time travel, why would you even care about citizenship in a country? $\endgroup$ – Tenryu Apr 10 '18 at 14:19

After the Bali Bombings, some Australians build a system for quickly identifying remains against DNA from close relatives. The point of it was to ensure that the right remains were being returned to the right family members for appropriate funerary rights. I don't know if it was the first time that this approach had been used, but it was certainly a big deal in Australia and it was the first time that such a thing had been done to identify remains on a mass scale for Australian families.

My understanding of this is that 'not store bought dirt's' allegedly naive comment is not really so naive. Most paternity testing is looking for genetic similarity because the problem of which person would be the child and which one would be the parent is apparently solved already. So the idea is that if there is a 50% match, then the father is the father. In a case where time travel is involved, the mother would still have a 50% similarity, and therefore if you think the problem is solved, then the mother could easily pass for the child.

Of course, if you have a father ALSO with 50% simliarity trying to pull the same trick, a careful check may reveal that something's up, but it's certainly possible that two children (to two different fathers) might have a genetic makeup that matches the parents in this fashion.

As for them being siblings; that's a little more complicated as I understand it and the people who do this victim identification through DNA will have a more complete answer than I would but it's possible for siblings to have much more or much less than 50% of their genetics in common, depending on what parts of the genetic code have been shared by which parent and how close they were to begin with genetically. Siblings with close to 50% similarity would actually be reasonably rare, and one would expect that if there is a reasonably close similarity between the parents in the first place that you'd be looking at around 70% or more similarity (those who know better, post comments and I'll edit accordingly if necessary) in most cases.

So there are limits to how this would work, but in theory it's possible to establish a biological relationship that could be misinterpreted due to relative ages of the parties, but as to whether or not that would establish enough of a legal case for citizenship of a specific country, that is a matter for each country.

England (for example) offers automatic citizenship for the children of expatriates, even if they never set foot in the country (the Australian Federal Government has been running afoul of this problem for the last year or so in dual-citizengate) but other countries have a broad spectrum of laws around this and don't always offer citizenship to families.

I recommend consulting an immigration consultant (yes, that's a thing apparently) before starting your work on a time travel machine as individual results may vary.


There could be exclusion of the father as a child of a female child by Mitochondrial DNA. Mitochondria are passed only from mother to child, so a man has the same as his mother but different from his children.

A lot of doubt could be cast on the parents being half siblings. Half-siblings typically share 1/4 of their genes, but the parents wouldn't be expected to share any more than typical members of their ethnicities. Modern tests will check 35 genes, which would mean 1 in 10 billion or so would be expected to test that way, but there haven't been anything like 10 billion half siblings in human history, so it would be unlikely.

These tests typically give a representation of genes set side by side, and the pattern is pretty clear for patents with a child of theirs, so if the three DNA analysis were ever on the same page a casual glance would suggest the truth. It may be possible automated checking wouldn't catch an unexpected relationship, but since most of these places subsist on paternity tests I doubt it.


For separate common paternity and maternity tests like immigration might do they may pass, but anything more advanced would very likely be caught.


would a DNA maternity test seem to indicate that you are the child of your child?

Of course not, since it has your combined DNA, not vice versa.

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    $\begingroup$ Naively my mother shares half her genes with both my grandmother and me (different sets of course), what is the difference exactly? $\endgroup$ – user25818 Apr 9 '18 at 22:56
  • $\begingroup$ Mathematically, you share half, but in reality your mother gets a "random" 3.2 billion base pairs from her mother and an equal "random" 3.2 billion from her father. You get a random 3.2 billion from your mother and a random 3.2 billion from your father. Thus, the average person gets 25% of her DNA from each of her 4 grandparents. But... we're individuals, and each non-"identical twin" sibling gets a different 3.2 billion genes from each parent. That's why you don't look like your sister. $\endgroup$ – RonJohn Apr 10 '18 at 0:37

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