Adam Lived 60,000 Years Ago, Not 6000

Great Debates
1

Gee, was there a misprint in the bible? :smiley:

Actually, according to National Geographic genetic studies have determined that everyone of us can be traced back to a man who lived 60,000 years ago. All decendants of other homo sapiens males had been wiped out. Consider that homo sapiens had been around for at least another 120,000 years.

What happened to these other guys?

I’m trying to draw scenarios as to how this might have happened, and the only thing I can think of is that a patriarch of a powerful family tribe roamed all of Africa killing off all the men and boys and raped their women. When they finished Africa they decided to head north east, and not finding anybody finally had to settle down.

Seriously though, has anybody got a better explanation?

2

Branches of a family tree terminate all of the time. We shouldn’t be surprised to know that this was so back then as well.

3

Yes, although I have to say I don’t understand this fully so there may and probably will be mistakes.

First off, it doesn’t mean that this guy was resonsible for all pregnancies then; for starters, if we imagine A as this guy and B as another, all it takes is for A’s son C to have a child E with B’s daughter D for them to trace back E. And of course now all of E’s descendants can be drawn back to A. The gap between A and C can be much larger than father and son; A himself may have had only the normal amount of kids back then. All it requires is that some point in history one of A’s relatives has had a kid with someone who was not A’s relative.

And secondly, you’re not taking into account that an entire line of not-A’s relatives could just have died out.

4

120,000 years of branches?

Humans have inhabited North America for 12,000 years, not 120,000 years. Can you imagine that all our lineages disappear except for one?

5

if Adam’s great great grandson had a child with adam’s brother’s great great granddaughter, the child would be a descendant of adam’s brother who wasn’t “killed off”.

You don’t have to kill off a huge percentage of the population to find a common ancenstor. In fact, the further back in time you go, the easier it gets to find a common ancestor for any group of people you care to examine.

6

In 12,000 years, everyone in America will likely be able to trace their ancestry back to a single common person. That certainly doesn’t mean that everyone else alive today is about to be suddenly killed off.

7

Oh, yeah? Well, if X did ____, Y would say Z! I learned that here at the S,D,M&B. I didn’t know that when I woke up this morning. Learning is good.

8

The fact that genetic studies have determined that every one of us can be traced back to a man who lived 60,000 years ago does not necessarily lead to all descendants of other Homo sapiens males had been wiped out. It just means that that one man is ancestor of everyone; it doesn’t exclude anyone else being an ancestor.

As a simple example: in the population of me and my cousins, our common grandfather is an ancestor to all of us. But, we all have other male ancestors in that same generation. Their lineages are still extant, but their descendants do not constitute the entire population like the grandfather’s in common do.

Read the Wikipedia entry on most recent common ancestor for an overview of the basics.

9

I’ve got two parents, four grandparents, eight great-grandparents, etc.: for any previous generation that’s n generations before me, I’ve got 2 to the power of n ancestors (barring overlap).

If we assume a 25-year generation (a pretty high assumption, I think), then over 60,000 years, you’re talking about 2400 generations. 2 to the power of 2400 is a pretty large number, to put it mildly. (2 to the power of 24 already gets us to 35 million ancestors, barring duplication).

It doesn’t seem surprising that if you go back that far, eventually everybody’s got one ancestor in common with everybody else. The particular guy who is that one ancestor may have been completely random, may have had just two kids (if he had just one kid, that kid would also be everyone’s ancestor).

Daniel

10

family trees don’t just branch out, we are descended from two parents, so the intermarriage relinks lineages. Over the course of 60,000 years the DNA recombines over and over. In another thousand years many more millions of people will be descended from Genghis Khan. That doesn’t mean that the descendants of King Richard disappeared. There will probably be descendants of both Genghis Khan and King Richard, though Genghis Khan will be more prevalent than King Richard because he was more prolific. That doesn’t mean that this biological Adam was our only ancestor alive at that time, only that he was one that unites all of us.

11

For my edification, what does “overlap” mean in this context? Something like a mother and father being siblings?

12

This actually is pretty simple to understand.

Imagine a population of 4 people, 2 men and 2 women. They pair off, and each pair has two kids, so that the next generation has 4 people as well. The first couple has 2 boys, the second couple has 2 girls. When the next generation pairs off and has kids, none of those kids will inherit the Y chromosome of the second male, because all his kids were girls. Every Y chromosome from now on will be inherited from the first male. And it doesn’t mean that every other male died, or didn’t have any kids, just that his kids were all girls.

Now extend that to thousands of people and thousands of generations. When a man fathers only girls, his Y chromosome doesn’t get passed on. Yet Y chromosomes have to pass on from generation to generation, unless one generation is so small that no boys are born, and the species becomes extinct. Eventually in any interbreeding population with multiple Y lineages, one Y lineage will go extinct if through random fluctuations every male who has that Y happens to have only daughters.

So, one guy 60,000 years ago fathered a boy who fathered a boy who fathered a boy who fathered a boy, and even though there were plenty of other men around who also fathered boys, at some point in the family of each of those men no boys were fathered, only girls, and their Y chromosome lineage became extinct.

If we look at the family tree of every human being on earth, they’ll have a branch for their father and mother, then their father’s father and mother and their mother’s father and mother, and so on. So everyone on earth has an ancestor who was an unbroken paternal ancestor, just like everyone on earth has an ancestor who was an unbroken maternal ancestor. You father had a father, his father had a father, his father had a father, his father had a father, and so on, back to the first sexual organisms. At the last time everyone’s father’s father’s father’s father’s father’s father was the same guy was 60,000 years ago, according to this study. So this is the reason that although Y lineages can go extinct, of course every Y lineage can’t go extinct.

And the reason we can tell this, is that Y chromosomes are passed on exclusively along the paternal line, just like mitochondria are passed on exclusively along the materal line.

And note that there were certainly other individuals who would be the paternal ancestor of all living humans, it’s just that this guy 60,000 years ago was just the latest one. Anyone earlier than him who was a paternal ancestor of all humans would have passed on their Y chromosome through him, and so it’s not possible to determine any other earlier common ancestors.

Of course, note the confounding factor that the Y chromosome that determines sex doesn’t always stay the same chromosome. For various complicated reasons, the chromosome that determines maleness loses more and more genes until the only things left are the genes that determine maleness. Then that tiny stub of a Y can get fused with another chromosome, and that chromosome becomes the new Y, and eventually all the genes get whittled away again. So the Y lineage doesn’t go all the way back to the first sexual organisms hundreds of millions of years ago. I’m not sure how long the human lineage has had our current sex determining chromosomes, but it hasn’t been that long.

13

More likely to be second or third or fourth (etc.) cousins gettin’ it on, which happens all the time. My matrilineal great-grandparents were third cousins without realising it until well after they were married.

And of course there was some stuff going on we’d now consider incest. In my family tree, one of my distant ancestors married his niece. But I turned out OK. :twitch:

14

Sure, but usually that close of relationship. If your mother and father were cousins, you’ll have only 2 grandparents, because your mother’s parents will be the same people as your father’s parents. Or if it was one generation farther back, you’d have 4 great-grandparents instead of 8, because the same person will fill more than one slot in that family tree. In small villages where everyone is related to everyone else, ancestor collapse can be quite profound, the same names show up over and over in different slots in everyone’s family tree.

So go back 60,000 years and eventually the paternal ancestor of every one of your ancestors will be filled in with the same name. And this won’t be because he was the only male who fathered children in his generation, just that all the others at some point had female children only. And the same thing on the maternal line, go back and there will be one name on all the maternal ancestor lines. But that maternal ancestor and that paternal ancestor probably never met, and lived in different generations.

Of course, for some species it is literally true that at one point there was only one male and one female who mated and were ancestors of all later members of that species, lots of island endemic species were probably founded this way with one gravid female washing up on an island by accident. And perhaps the human lineage passed through such a bottleneck at one point, although we don’t have any evidence of it.

15

I’m getting it guys. but if I look at it the other way, Seeing how patriarchal families bloom expontentially with each generation , roughly 50% males, and given enough generations to overcome probabilities of a wipeout by war, famine, disease or disproportionate gender production, its difficult to see how so many paternal lineages got wiped out

16

Y-chromosome “Adam” is the patrilinial ancestor of all of us. Your father’s father’s father’s … father. We all had lots of other male ancestors, but the rest go thru the maternal line at some point.

Same with mtDNA “Eve”. She’s our common female ancestor thru the maternal line only.

17

They weren’t wiped out; they’re incorporated into the lineage of this guy. His friend Bob might be related to 70% of all of us around today. He’s just at the top of the lineage that links everyone (in patrilinear terms), and only the most recent one at that.

18

…And that man was the legendary Wilt Chamberlain.

19

…And now you know…The Rest of the Story.

20

As said, they don’t get wiped out; they just over time marry into other male lines. If one were to count both female and male lines, they didn’t die out at all. Given time it’s inevitable that fewer and fewer lines predominate; I’ve heard this is a problem in China, since it’s so old. They simply don’t have as many family names as a younger culture, which leads to situations like having a trial where the accused, judge and prosecutor all have the same name, along with a suspect mistakenly arrested because of his name.

There is some evidence that there was such a bottleneck.