But how would they possibly know if their great-great-great-great-grandmother was one-sixteenth Malayan?
Well, if you have a second hand anecdote from a party with a personal stake, that’s completely different. Clearly there is no need for any other evidence. When science and logic contradict baseless anecdote, clearly we should believe the anecdote :rolleyes:
Never mind that. Literacy rates among “full blooded” aborigines just 60 years ago were less than 10%, and most births were undocumented because Aborigines weren’t included in any census.
So it would be extraordinary if anyone could even positively identify 8 Aboriginal Great Grandparents, let alone be sure of their ancestry beyond that point.
We aren’t talking Great-great-great-great-grandparents here. I am highly skeptical that anyone even knows the *name *of more than half their Aboriginal great grandparents, and that’s assuming a 20 year generation span.
I don’t think it’s rather different. It seems clear to me that the incest taboo most likely arose from a moralization of the Westermarck Effect (i.e. “I would never want to mate with my sister, that’s gross! No one else should, either!”)
But dude, your sister’s hot.
I’m wondering what you are even doing on the General Questions section of the Straight Dope Message Boards. Arguing on the internet is what we do here, believing anecdotes over evidence is what we don’t do.
No one has mentioned the Sentinelese.
Also, let’s remember that, even if the MRCA lived at the time of Christ, there are plenty of people that have absolutely none of his genes, because there’ve been so many generation between then and now.
Not necessarily: the half of my family which doesn’t consider first-cousins taboo is from a place where there is a lot of genetic variation. The half which considers second-cousins taboo is from a place with a lot less genetic variation: avoiding “mixing blood that’s too close” requires going further away when you know that climbing any branch of the family tree will lead to a common pair of ancestors eventually (just as a completely random piece of data, a study of the family trees of my 40-students 11th-grade class, where each tree was available going up to 1700, found common ancestors for any of us with two to six other students; we were in the area the no-cousins side of my family hails from).
Even MRCA can be misleading since a group of people could all be 50th cousins at most, while not having a common ancestor much earlier than that. Of course, any two would have to have a common ancestor within the past 50 generations, but that is not the same as the whole population having a common ancestor within 50 generations.
Perhaps an example would help. Imagine just three people, Alice, Bob, and Charles. Alice’s parents are Don and Edith. Bob’s parents are Edith’s brother Frank and Gloria. Charles’s parents are Gloria’s brother Hank and Don’s sister Irene. Assuming no other relationship, Alice and Bob, Bob and Charles, and Charles and Alice are all first cousin’s but they have no ancestor closer than three generations ago.
I tend to be sceptical of arguments for a relatively recent MRCA. These arguments disregard the existence of “fat tails,” statistical outliers that are more extreme than analyses would suggest - the same reason why once-a-millennium events happen in the financial markets every few years. They also disregard the existence of radically isolated populations, such as the Sentinelese and some of the peoples of New Guinea, and the likelihood that at least some Native Americans have no European or African ancestry (e.g., in some of the uncontacted or minimally contacted tribes of South America). Consider also that there are still purebred Hawaiians, and while the pre-James Cook Hawaiians were not radically isolated, they were still pretty isolated.
As far as the OP’s question is concerned, however: I doubt if either he or his girlfriend are from radically isolated populations. They’re sure to be much closer than 50th cousins. The chances that they are closer than 10th cousins are very high.
So what? How on earth is that a GQ response to the previous poster’s tentative assertion?
In any case, the actual answer seems to be that medieval canon law starting in the 9th century prohibited marriages within the 7th degree of kinship, not 17th.
First of all, Australia was not genetically isolated for that long. We know there was immigration from parts of Asia 4-5K years ago, at least. But further, once Europeans arrived, it would be extremely difficult to prevent gene flow to even the most remote tribes given 300 years of interbreeding.
I would have no reason to believe they had any way of knowing that.
So jesus and I are cousins?
On which side? His mother’s or his father’s?
The problem with that argument is that it makes the alternative even more likely. If “fat tails” make a recent ancestor unlikely, it makes the presence of individuals with no common ancestors even more likely, simply because there are 6 billion ways to find a common ancestor, and only one way to avoid doing so.
No people of New Guinea are isolated, radically or otherwise. Some of the agriculturalists were isolated from other agriculturalists, but they all maintained contact and interbred with adjacent HGs.
The Sentinelese have also never been truly isolated. They are just too close geographically to other people. We know that Sentinelese words occur in other Andamanese langauges and we know from British records in the 19th century that there were Sentinelese actually *living *amongst the other Andamanese peoples. So long as one such event occurred every couple of generations, the Sentinelese are going to have the same ancestor as everyone else.
Given the tiny population of the Sentinels, if even one outsider found their way into the bloodline any time prior to 500 years ago, then the entire group will be descended from them. This is further exacerbated by the effect of disease and the evolutionary advantage of outside genetics providing immunity.
That would be astonishingly unlikely. The uncontacted tribes of South America are all village farmers and all are in contact with their neighbours, or were until 50 years ago. More importantly, they all seem to be descendants of the great agricultural kingdoms that were decimated from European disease. They aren’t people who have always lived like that, they are people whose ancestors just 500 years ago lived in cities under hereditary kings. There seems to be no way that they *could *be isolated.
Do you have a reference for this claim? It would be interesting to see how anyone would establish such a fact, given that the Hawaiians had no written language. If an Hawaiian had a Tahitian ancestor born in 1066, how would they ever know? No English commoner could prove that they had no single French ancestor from 1066, and that is a literate culture with some of the world’s best written records. I can’t see how an Hawaiian could ever be certain that they had no Tahitian ancestry from the same date.
And that is the reason why Hawaiians can’t be described as being in any way isolated. We know they weren’t radically isolated, to the extent that Hawaiian is mutually intelligible with other Polynesian languages. From both linguistic and archaeological evidence we can be sure that Hawaiians were in constant cohabitation, not just occasional contact, with the outside world until just 800 years ago. It seems likely that the last common ancestor of Hawaiians and other Polynesians is less than 1, 500 years back. That would makes the Hawaiians less isolated than Europeans.
And “7th degree of kinship” doesn’t mean 7th cousin, either. Kin in the 7th degree would be, for example, third cousins once removed (or second cousins 3 times removed, etc., though that makes marriages rather unlike just by virtue of age).
Correcting myself: 2nd cousins once removed. Which, yeah, is a bit further than most modern cultures take it, but really not all that far.
Hmmm… the magic-50 I remember was used for a different statistic: “There are only 50 ‘real’ people on earth.” By that they meant there are only 50 distinct facial features in adult humans identified. This cuts across race, mind. It was an expansion of the separated-at-birth concept. Yep, read it from time when I was young.
All this talk of MRCA is unnecessary. That unknown person is the mother or father of all humanity, but that’s not what the OP is asking about. The OP wants to know what generation, i.e. what set of ancestors, would be enough to find some path from each living person to every other living person.
The difference is that a single ancestor needn’t be present in every “relation chain” from living person to living person, like the MRCA demands. If we mapped out every lineage going back only, say, 4 generations and had enough people to connect everyone in at least one manner, then we’d say everyone is 2nd cousins even if the MRCA isn’t in that generation.
An example would be two couples who have kids and then switch partners to have more kids. Every kid would share at least one parent with every other kid, but no common ancestor would exist within this set. And since humanity’s female MRCA never knew the male MRCA, you can’t disqualify this set of kids just because they’re not full siblings.
Nitpick: You mean the female-line MRCA and male-line. Everyone’s father’s father’s father’s … father was Y-Adam, and so he was most certainly a common ancestor of all humanity, but his mother was also, therefore, a common ancestor of all humanity. And the mixed-line MRCA was much more recent than either Y-Adam or Mitochondrial Eve.
I can’t make sense of this.
To start with, I can’t see any possible way that every kid would share at least one parent with every other kid. It seems mathematically impossible since there are a minimum of 4 children, but a maximum of 2 permutations of parents
John and Jane have a kid: Bob
Kath and Ken have a kid: Carol
Kath and John then have a kid: Ted
Jane and Ken then have a kid: Alice
Ted doesn’t share any common parentage at all with with Alice. Ted’s parents are Kath and John. Alice’s parents are Jane and Ken. Ted and Alice are genetically utterly unrelated.
In order to find a path from each living person to every other living person within this group, you will need to go back and find an ancestor that is shared by both Ted and Alice. If John’s Grandfather and Ken’s Great Grandfather are the same person, Engelbert, then you will have a path linking all these people. But that would make that Engelbert the MRCA .
If we mapped out every lineage going back 4 generations, the only way we I can see that we could have enough people to connect everyone in at least one manner is if the MRCA occurred within four generations.
I’m guessing I’m missing something here.
Perhaps you are working form a position that “step sibling” or adopted sibling or other relationships that have no objective or genetic basis are sufficient to establish a relation chain. But I don’t think that’s what the OP wants. Since he is talking about incest, relationships that only exist culturally, with no genetic relationship at all, hardly seem to fit.