Timeline for In a world with time travel, would it be possible to be your own mother's mother?
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13 events
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| Mar 5, 2020 at 16:06 | comment | added | Upper_Case | @Thymine What David K said basically covers it. The OP has placed a constraint on time travel that the past cannot be changed. That can be interpreted as either changes are "silent" (all outcomes are unchanged) or that literally no changes of any kind can be made. In either interpretation, no change in subsequent generations can be introduced, and so no genetic bottlenecking can occur in the traveler or her mother. It's all time magic anyways, but since no new factors can be introduced (arbitrary constraint from the question), then no inbreeding factors can be introduced either. | |
| Mar 5, 2020 at 13:36 | comment | added | David K | The situation posited in the question is a non-isolated causal loop. The answers seem to be along two lines. One line of thought rejects the basic premise of a non-isolated causal loop; because there is input from outside the loop, it cannot be stable. This is one of those answers. The objections are couched in technicalities of genetics but these are just examples of the rejection of the non-isolated causal loop. The other answers accept the basic premise. If you accept the basic premise, the genetics fall into place. | |
| Mar 5, 2020 at 13:10 | vote | accept | sebrockm | ||
| Mar 5, 2020 at 9:37 | comment | added | Thymine | @Mayken Oh, right, the original grandmother/grandfather would still provide it. My bad. Okay but then it means that if a girl replaces her maternal grandfather, then she passes on a different mitochondrial genome than the one originally passed on. Which creates a genetic paradox, and the only way to solve it is if both grandmothers happened to have the same mitochondria. This isn't a bootstrap paradox but instead a change in events which could be scientifically verified, which the OP says is not allowed in this scenario. We should use mitochondrial DNA to screen for time travellers | |
| Mar 5, 2020 at 9:19 | comment | added | Thymine | @Upper_Case I don't think in-breeding is a non-factor. In-breeding wouldn't cause the outcome to be any different (or worse) than it is in the original timeline, but if the only way for this person to be born in the original timeline requires their mother and father to share 2/3 of their genetic variants, which are also partially shared with F1, then in the original timeline this family has the beginnings of an in-breeding problem. I think it's simpler to just assume genetically distinct backgrounds in the family and that the time travel mathemagically deal with the unlikelihood. | |
| Mar 5, 2020 at 6:24 | comment | added | Makyen | Your last paragraph is wrong. It assumes the time traveler must be the source for the mitochondrial genome or that they must be the source for the Y chromosome; neither is actually required. Those can be supplied by any other identical source of that specific genetic material, just like every other part of the traveler's DNA which isn't directly provided by the traveler. In theory, the time traveler could replace any of their ancestors, because what the ancestor contributes to the time traveler is always a subset of the time traveler's DNA, which the traveler can always provide. | |
| Mar 4, 2020 at 17:29 | comment | added | Upper_Case | @sebrockm If this time traveling escapade can only produce the exact same set of genetic information each time, then breeding (in- or otherwise) is a non-factor. By pre-defining the outcome as "exactly the same in every way", none of the factors which impact breeding will apply-- there fundamentally cannot be any changes. | |
| Mar 4, 2020 at 15:41 | comment | added | sebrockm | Yes, precisely. The mitochondrial DNA would be a bootstrap paradox because none of the fathers can inherit theirs. Also, I don't see an issue with M1 not providing anything new. None of us provides anything new. We all just shake what our mamas (and papas) gave us ;) But of course that would be a very high level of in-breeding. Do you see a biological issue with that in this particular case? | |
| Mar 4, 2020 at 15:10 | comment | added | Thymine | Okay, I think I see what you're trying to do. The problem is that this means M1 doesn't contribute anything new. Essentially, instead of solving how you could have M1 contain part of the genetic material to be her own grandmother, you figured out how to make F1 and F2 contain all of the necessary genetic material to create M1's DNA without M1's involvement. As you said, M1 is 1/3 of F1 and 2/3 of F2, so F1 and F2's DNA is sufficient to generate M1, there is no bootstrap paradox but there's a very high level of in-breeding in that scenario | |
| Mar 4, 2020 at 14:55 | comment | added | sebrockm | Well, the 1/3 comes out of nowhere. The mother and daughter (or rather their genes) are a bootstrap paradox. Maybe with the exception of the mitochondrial DNA, they just happen to be identical by 1/3 and 2/3 with the two fathers. Why? Because then the math works out. By "mixing in" 50% of the genes of the "1/3-father" your daughter will again have that 1/3 2/3 ratio, just vice versa. And by having that ratio, when she has a child with the other father, that child can genetically be you, because that will switch the ratio again. I hope what I'm saying makes any sense :-D | |
| Mar 4, 2020 at 14:45 | comment | added | Thymine | @sebrockm I think so, to be honest I'm having trouble following your math, I don't see how you get 1/3 anywhere. But yes, the father provides 1/2 and the maternal grandfather provides the last 1/4, as they have in the original timeline. You provide 1/4 as a grandmother which you definitely would have. It's unlikely for all the meiosis events to line up perfectly, but your world takes care of pesky probability so it's all good and doesn't violate any biological mechanisms that I know of. | |
| Mar 4, 2020 at 14:39 | comment | added | sebrockm | This is precisely the kind of answer I was hoping for! +1 I was especially unsure of the meiosis process, so thanks for explaining that. The scenario you describe in the second half of your answer sounds similar to my 2nd proposal where the two fathers provide the "missing" DNA you need to be your grandmother, if I understand you correctly? Because that part you cannot have gotten from your mother because of 1/2*1/2 = 1/4. | |
| Mar 4, 2020 at 14:14 | history | answered | Thymine | CC BY-SA 4.0 |