It’s probable there’s many people out there who share none of my ancestry for a full thirty generations back,
Yep. The most recent common ancestor of living humans lived at least a couple millennia (i.e. about seventy generations) ago. (EDIT: I’m not fully convinced that that implies that for any time t later than that, there’s at least one with you no ancestry at time t. I’m too tired to trust my cognitive abilities right now.)
and there’s one who (probably) shares it completely.
Do you have any reason in particular to suspect that you and your sibling may have different biological fathers, or is the “probably” a 1-is-not-a-probability self-nitpick?
Do you have any reason in particular to suspect that you and your sibling may have different biological fathers, or is the “probably” a 1-is-not-a-probability self-nitpick?
It’s not “1-is-not-a-probability” so much as it is “the base rate of this is not 0″; there’s also the chance that I was switched at birth (hospitals are much better at avoiding this now than they have been in the past). If my family signs up for 23andMe, then the probability will either shoot up towards 1 or drop down to negligible, but until then I’m going with the base rate.
Really during your life you haven’t encountered much net evidence towards either direction shifting your probability assignment away from the base rate, e.g. how much you look like your parents, whether you share some uncommon medical condition with either of them, blood type, etc.?
I have very little expertise in quantifying the effect of that evidence, and in the aggregate it doesn’t seem strong enough to make the probability negligible or large.
The strategic concerns here are also amusing to ponder. (There’s several reasons that 23andMe shows you 2nd and higher cousins with no prompting, but wants your approval before they show you first cousins.) The more one suspects being swapped at birth, the more important it is to find one’s birth family for health prediction. But, I’ve had my SNPs read, which I imagine screens off much of the benefit of knowing family history for medical conditions. It’s also less damaging to the existing family structure: most people who learn they were swapped at birth maintain their relationship with the parents that raised them, and also gain some sort of relationship with their genetic parents.
If you suspect infidelity, though, then the picture is very different. Again, learning your birth father tells you something about health, and may be a valuable social relationship (for one, they may not have any other children; in the swap case, there’s someone else in the mirror of your situation); it’s probably tremendously destructive to your current family arrangement, though.
Yep. The most recent common ancestor of living humans lived at least a couple millennia (i.e. about seventy generations) ago. (EDIT: I’m not fully convinced that that implies that for any time t later than that, there’s at least one with you no ancestry at time t. I’m too tired to trust my cognitive abilities right now.)
Do you have any reason in particular to suspect that you and your sibling may have different biological fathers, or is the “probably” a 1-is-not-a-probability self-nitpick?
It’s not “1-is-not-a-probability” so much as it is “the base rate of this is not 0″; there’s also the chance that I was switched at birth (hospitals are much better at avoiding this now than they have been in the past). If my family signs up for 23andMe, then the probability will either shoot up towards 1 or drop down to negligible, but until then I’m going with the base rate.
Really during your life you haven’t encountered much net evidence towards either direction shifting your probability assignment away from the base rate, e.g. how much you look like your parents, whether you share some uncommon medical condition with either of them, blood type, etc.?
I have very little expertise in quantifying the effect of that evidence, and in the aggregate it doesn’t seem strong enough to make the probability negligible or large.
The strategic concerns here are also amusing to ponder. (There’s several reasons that 23andMe shows you 2nd and higher cousins with no prompting, but wants your approval before they show you first cousins.) The more one suspects being swapped at birth, the more important it is to find one’s birth family for health prediction. But, I’ve had my SNPs read, which I imagine screens off much of the benefit of knowing family history for medical conditions. It’s also less damaging to the existing family structure: most people who learn they were swapped at birth maintain their relationship with the parents that raised them, and also gain some sort of relationship with their genetic parents.
If you suspect infidelity, though, then the picture is very different. Again, learning your birth father tells you something about health, and may be a valuable social relationship (for one, they may not have any other children; in the swap case, there’s someone else in the mirror of your situation); it’s probably tremendously destructive to your current family arrangement, though.