How many ancestors do we have?

[allan2]

Something I just thought of:

Say a generation is, on average, 25 years. Each past generation of ancestors is multiplied by two as you go back--i.e. a person has two parents, 4 grandparents, 8 great-grandparents, 16 great-greats, etc.

So if you go back far enough, say 30 generations, that is 2 to the 30th or 1,073,741,824 ancestors! And 30 times our average of 25 years per generation would be 750 years ago--the year 1250 AD roughly.

Now even giving or taking a century or two for the different ages people would have been when they had their children, I'm still not sure there were over a billion people living in the span between 1050 and 1450 AD. Well, maybe there were, but go back another 5 or ten generations and the number is obviously impossible.

Now obviously I'm missing something here that will sound obvious when someone points it out to me. I can see cousins marrying each other (and hence some redundancies in the ancestry), but THAT many? It just sounds strange....

But I wonder if there is a certain number of generations back, beyond which EVERYBODY living at a certain time could be said with some certainty to be an ancestor of ANY randomly-picked person living today (heck, an ancestor of ALL of us)--provided of course they had any children at all....

 

[ainwood]

I think you are being a bit mislead by the numbers. If people have siblings, then they can share common parents. They can also share common grandparents etc, which will greatly (inverse-exponentially) reduce the numbers of people.

One interesting fact that I read somewhere is that there are more people alive on earth at the moment than have ever lived before.

But on the "single common ancestor" thing, I think you're right. I read an article on this at some stage, where DNA records had been used to trace common ancestors - I'll try to dig out the reference.

 

[allan2]

I thought some more and saw that people can marry cousins SEVERAL times removed, and not even know they are so distantly related. Perhaps that's it. Then there would be "redundancies" in the ancestry....

But yes, it would be fascinating to think that 1000 years ago or so, I could pick ANYONE living at that time (from Norman the Conqueror to a Chinese silk merchant to a nomadic herdsman in Africa) and say with some statistical certainty that I am descended from that person, provided of course that that person had children, who had children....

I now remember someone once telling me that we are all (everyone on the planet today) likely cousins nine times or less removed. I wonder if that's true too....

(BTW, I also remember reading once that there were an estimated 76 billion people who have ever lived on this planet over the span of human existence. Have they vastly modified that number? I think I read this sometime in the 70s.)

 

[BlueMonday]

Perhaps you're thinking about it in the wrong direction. If we all have one common ancestor than you should go from parent to child, not child to parent. Certainly, in the early stages of man inbreeding wasn't a choice, it was a necessity. In a small, family oriented community you'd only have a few suitable mates for a male and they most likely would be close siblings.

BlueMonday's daily fun fact: Geneticists and Antrhopologists have retraced family DNA strings using the Mitochondria in your cells. During conception the DNA that is used to make the human body is split half and half with 23 chromosomes coming from the sperm and 23 chromosomes coming from the egg. However, there is a second storage of DNA in an animal cell, the Mitochondria. Unlike the reproductive DNA, the Mitochondria contain a duplicate of your mother's Mitochondrial DNA. So in each family of humans, Mitochrondrial DNA is indentical along the female blood lines. So your grandmother (on your mother's side) has the same Mitochrondrial DNA as your mother, and you have the same Mitochondrial DNA as her, but if you're male, when you have children they will have your wife's Mitochondrial DNA, not yours.

Now, The Mitochrondrial DNA mutate at a steady rate, so every few generations the Mitochondrial DNA will alter themselves slightly. By measuring the differences in Mitochondrial DNA in people all over the globe scientists were able to deduce that all humans on the Earth right now are descended from four families of humans that existed after the time of the last great extinction (about 650,000 years ago). Before then there may have been hundreds of families, but after the great extinction only four (that we know of) remained to create the billions of people on the face of the Earth now.

...Special thanks to the Discovery Channel for all that fun info.

 

[Zwelgje]

Originally posted by BlueMonday
but after the great extinction only four (that we know of) remained to create the billions of people on the face of the Earth now.

Scary isn't it that humans had almost become exstinct, imagine what the world would look like now.

 

[Zwelgje]

Mitochondria are believed to be single-cell organisms that entered the cells of multicellular organisms millions of years ago. The mitochondria were by doing this protected and the mitochondria would give energy to the cells of the multicellular organism. In fact nowadays our cells heavily depend upon mitochondria as a source of energy. Without mitochondria life as we know it wouldn't be possible.
Thanks to my professor in cell-biology for that information.

 

[Ouchgeddon]

Right on about the mitochondria. In fact Star Wars Episode 1 had a little discussion about "midichlorians" being "symbioms" with us, causing the Force powers. Which sounds straight out of Parasite Eve, which has our mitochondria either rebelling or giving us magi like powers.

I also read that the y-chromosome is a useful marker, that was used to trace a guy's lineage back to a stoen age man. The y-chromosome hardly changes at all throughout the generations, as it does not "compete" with genes from the mother's side. Dad gives you either an x which gets it on with your mom's x, or a y that sits idly by mom's x.

 

[Zwelgje]

Originally posted by Ouchgeddon
I also read that the y-chromosome is a useful marker, that was used to trace a guy's lineage back to a stoen age man. The y-chromosome hardly changes at all throughout the generations, as it does not "compete" with genes from the mother's side. Dad gives you either an x which gets it on with your mom's x, or a y that sits idly by mom's x.

I haven't read about the Y chromosome but it could very well be true as you inherit it from your dad and the mother hasn't got any interference with it.
A woman has two X chromosomes but she really doesn't use one of them, it's just turned off and lies in the nucleus of the cell doing nothing.

 

[allan2]

"scientists were able to deduce that all humans on the Earth right now are descended from four families of humans that existed after the time of the last great extinction (about 650,000 years ago)."

That would be strictly through the matrilineal line--one line out of millions of possible ancestral lines.... What about the mother of the father of your maternal grandfather, or other such permutations?

Take ALL the ancestors, not just the mother of the mother of the mother..., and I wonder if as little as 1000 years ago, we all can claim some heritage from anyone living at that time (again, providing they ever procreated at all and put their genes into the gene pool). We're talking about 2 to the 40th different ancestry permutations here....

Anyone besides me ever hear of the theory that we are all likely cousins 9th removed or less--i.e. take any two people, and go back 9 generations, that they would have at least ONE common ancestor out of their 2-to-the-ninth (512) other ones going 9 back (actually, including all ancestors up to the ninth, the number would be 1027)? That sounds farfetched, but perhaps anyone more familiar with probability laws could clarify that one....

 

[CrazyScientist]

Originally posted by Ouchgeddon
Right on about the mitochondria. In fact Star Wars Episode 1 had a little discussion about "midichlorians" being "symbioms" with us, causing the Force powers. Which sounds straight out of Parasite Eve, which has our mitochondria either rebelling or giving us magi like powers.

I also read that the y-chromosome is a useful marker, that was used to trace a guy's lineage back to a stoen age man. The y-chromosome hardly changes at all throughout the generations, as it does not "compete" with genes from the mother's side. Dad gives you either an x which gets it on with your mom's x, or a y that sits idly by mom's x.

Actually there are now theories that these chromosomes do occasioanlly "compete" resulting in changes in the Y-chromosome (usually it's reduction in size).

Imagine if you will a mutation on the x chromosome that increased the fitness or fertility of the women that carried it, but had the side-effect of killing any sperm carrying the y-chromosome. This gene would carry a selective advantage, and thus proliferate within the population, but it's bearers would produce only female children. The eventual result of such a mutation would be a reduction in the male population such that the only males left would be those with a y-chromosome that lacked whatever DNA sequences allowed it to be recognized by this y-killing protein.
Bizarre huh? Yet they think it has happened a few times in fairly recent evolutionary history, which is why the y-chromosome is so puny compared to the x. It loses a few genes each time such an anti-y mutation occurs to "disguise" themselves. Theory is, it may even have happened one or more times since our split with the chimps (presumably because chimps have a slightly bigger y chromosome than humans).

I too have heard that there are as many people alive today as have ever lived, but have never seen data on it or anything, just word of mouth so I can;t be sure. This would make sense, though considering exponential population growth.

 

[andyo]

Originally posted by DamnCommie

I too have heard that there are as many people alive today as have ever lived, but have never seen data on it or anything, just word of mouth so I can;t be sure. This would make sense, though considering exponential population growth.

this doesn't make any sense - yes - there are a couple of billion people living today - but how many people were living last year - pretty close to the amount this year - now if you take all those people living last year, as well as all the people who ever lived, that would be way more than the people currently alive

 

[Bamspeedy]

If you believe the bible......I can trace my ancestry back to Adam and Eve!

Well, my mom traced by ancestry back to some Norwegian kings (1000-1300 A.D. or something). Then she found that some historian/geneologist had traced the ancestry of one of those kings back to someone that was mentioned in the bible. Tracing back through the Bible was able to trace ancestry back to Adam and Eve. 124 generations I think it was (give or take a few generations, I can't remember the exact number).

 

[BlueMonday]

Originally posted by andyo


this doesn't make any sense - yes - there are a couple of billion people living today - but how many people were living last year - pretty close to the amount this year - now if you take all those people living last year, as well as all the people who ever lived, that would be way more than the people currently alive

No, because we didn't all just die off last year and be reborn. A vast majority of the people who were alive a year ago are alive today. However, we have added dramatically to the population by birth.

Look at it this way: a decade ago we had 5 billion people on Earth. Today we have more than 6 billion. In another ten years we'll probably have more than 8 billion. At that rate of expontential expansion, it won't be long before there are more people living at one time than all the people beforehand.

It's all just a I=P*e^(R*T) formula.

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[Zwelgje]

You also could say it like this:
The amount of people living on earth today is bigger than the amount of people who have died.
Maybe it's true too....

 

[allhailIndia]

I remember reading somewhere that a 17000 year old lineage has been found between an English schoolteacher and a caveman's bones!!

I unfortunately cannot trace my history back very long, what with keeping track of a family where even second cousins twice removed recognise each other on the streets .

I can trace my ancestry only as far back as my granddad's great granddad, who was a general in the Army of Haider Ali

 

[FearlessLeader2]

Wow. Scientists have figured out that we had four families of common ancestors. That's amazing. I could have saved them some time and pointed out that after the Flood, Noah and his 3 sons 'went on to have many sons and daughters'.

 

[Zwelgje]

Well if you believe we're all related to Noah and his sons then the Bible really describes an event that happened 650,000 years ago. I hope you believe that the story was told for 648,000 years and then was written down in the Bible, I sure don't. Back then the people couldn't even speak......

 

[Zachriel]

According to the latest science, the Biblical story of Noah may have a basis in a specific historical event. Modern geology has demonstrated that the Black Sea was once separated from the Mediterranean. About 7000 years ago a channel was opened between the two seas and a great flood ensued as the basin of the Black Sea was filled. There is some evidence that stone age people may have populated this basin at the end of the last ice age.

National Geographic is exploring the bottom of the Black Sea looking for evidence of this "Noah" civilization. If this hypothesis is confirmed, it would be a very remarkable discovery.

http://www.nationalgeographic.com/blacksea/

 

[Ilúvatar]

I've heard about that before. I think they also say the famous old city of Catal Hüyük n Asia Minor is sort of evidence for a high civilization that doesn't have any outposts on other locations, so they suppose some very old hittite stuff might be on the ground of the Black Sea, thus giving some more insight into the actual development from stone age to city building such as Catal Hüyük.

 

[vonork]

Well if you pick any person on earth you will know them through your friends and there friends in I belive 5 or 6 steps.

So whoever you kill will be a friend of your friends friends...

Someday I might try to get a favour from the pope or bush through my friends frineds