Could DNA testing verify that someone was a time traveler?

If someone says they traveled through time to the present day, from the past or future, could DNA testing be used to verify their claims? Would there be something about their DNA itself which would indicate that the number of generations in their DNA lineage was significantly different than would be expected of people at the present? Or perhaps could the DNA databases from consumer DNA testing be used to determine that the person was the X-great grandparent or X-great grandchild of someone at the present time?

For instance, consider this news story:

“Cheddar Man” lived 10,000 years ago. Through genetic testing, they found that a nearby man, Adrian Targett, is related to Cheddar Man with 300 generations between them. If Cheddar Man traveled through time to the present day, could this kind of DNA testing be used to help verify his claims that he was a time traveler?

And if so, what about someone coming here from the future? Very doubtful, I’m sure.

If they come from the distant future or have edited genomes and have enough genetic changes that their DNA is significantly different than everyone else today, yes, that seems like a plausible indicator.

Seems easier if they are in a Back to the future type scenario - you’ve got a kid and his mother and father who are the same age, but the DNA tests say they are father/son and mother/son and the physical exams show no evidence of there ever being a pregnancy, and the ages make it impossible anyway. Seems much harder if you have a “distant past/future” type scenario.

Yes. DNA mutates at a steady rate each generation. The “molecular clock” is a powerful technique that is usually used to infer the time since two species diverged from a common ancestor, but could also be used to detect a time traveller from that far back - certainly if you could sequence the entire genome from a living time traveler. No single mutation would be a smoking gun, but the statistical pattern across the genome when compared to the modern human population (including polymorphisms in the modern human population) would tell you.

The article is somewhat misleading. This is based on mitochondrial DNA, which is inherited without recombination through the maternal line. In terms of mitochondrial DNA lineage, it is interesting - it shows that the mitochondrial DNA lineage of Cheddar man survives. But the fact that Cheddar Man and any given modern person are related is in itself unremarkable. If Cheddar Man is the ancestor of anyone alive today (his lineage did not die out) then it is overwhelmingly likely that he is the genealogical ancestor of everyone alive today in the UK, and quite likely that he’s an ancestor of everyone alive on earth. This is simply a function of the fact that everyone has two parents, so the number of ancestors doubles each generation as you look back (until inbreeding saturation, when two different genealogical paths trace back to the same individual).

The most recent common ancestor of all humans probably lived about 2,300 years ago. At around 5,000 years ago, you reach a point of probable identical ancestry - where every human alive today had the exact same entire set of ancestors. In other words, everyone alive at that time was either an ancestor of every modern human, or their lineage died out completely.

Rohde et al Nature 431, 562-566 (30 September 2004)
Modelling the recent common ancestry of all living humans | Nature

Not sure about the effect on DNA, but thanks to nuclear bomb testing in the '50s and '60s, if the traveler claimed to be born anytime between the '50’s to present day there are detectable levels of bomb carbon-14 spikes in organic tissue that can determine the truthfulness of that.

Aren’t there also similar DNA markers for exposure to viruses and the like? Perhaps a time traveler could have unique markers for diseases that don’t yet exist? Only guessing from things that were being discussed at the early stages of COVID.

Not in DNA, but in the adaptive immune system. We couldn’t detect antibodies to viruses that don’t yet exist, because we wouldn’t know what to look for. But the giveaway would be the broad absence of immunity to current viruses. If this time traveler is not isolated, they will die quickly because they lack immunity to our viruses, and they may be carrying viruses that will likewise kill us.

Are you thinking of this?

It depends on far they’re traveling. A time traveler from a hundred years in either direction from the present might be prone to getting ill for a bit with every variety of headcold making the rounds but would probably be OK.

What you would really have to worry about it someone from, say 1,000 years ago who might be carrying something like smallpox into the present day, or someone bringing something nasty from 1,000 years in the future.

Someone from 20,000 years in the past, when humans lived in small groups, is less likely to bring something nasty to the present since most of our worst diseases tend to be “crowd diseases” that didn’t arise until humans developed agriculture, domesticated animals, and started living in cities.

How would that work, given that there was a great distance between some populations, and great difficulty in travelling before modern times? How could one confidently draw that conclusion with regard to, say, an Amazonian tribesperson and someone from an equally remote part of Africa?

If there were random mating among all humans (no isolated subpopulations) the MRCA would be at just 800 years. The longer estimate of 2,300 years in the paper I linked (sorry I can’t find a free access link) derives from various models based on what we know of historical population structure.

Because of the doubling effect, even a single migrant into an isolated population can quickly become an ancestor of everyone in that population. So it takes very little migration to create genealogical paths that link everyone alive. Populations have not remained completely isolated in the past few hundred years.

If you were to ask the same question a few hundred years ago, the MRCA would have been more distant because there were probably populations (eg Tasmania) that had been completely isolated for millennia.

In addition to what Reimann mentions, not everyone has the same pattern of ancestors. Going 2300 years ago is about 90-100 generations, so you have 2^100 ancestors. There weren’t 2^100 people ever, much less 2300 years ago so everybody in that 2^100 full tree is duplicated billions of times. The pattern of who is duplicated in each tree will be very different for the people you mention. The African will have the people who lived in Africa back then many, many times more than those who lived in the western hemisphere even if the unique set of ancestors is the same for both.

I would think that for the specific example of the African and the Amazonian, the transatlantic slave trade provides a sad but obvious explanation for how this pattern of migration could have worked out. It’s easy to imagine an African slave brought to Brazil while this country was still importing slave (either under Portuguese colony rule or post-independence), plus some cases of interethnic relationships between whites, slaves, and Amazonians (not necessarily the same white person with both a slave and an Amazonian, obviously). And there you have it, the ancestries of subsequent generations of the Amazonian tribe and the Africans overlap.

I would have thought some people from remote parts of new guinea might not share ancestors for father back than 2300 years.