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A question that has intrigued me for ages

  1. May 18, 2007 #1
    I can remember thinking about this when I was 7. It's an unanswerable question but it's still interesting, I believe: Can we relate every person on earth by a tree of acquaintances? That is if we were to construct a stem diagram in which the first branch relates me and all the persons that I know personally, and the second branch the people I know with all the people they know, and so on, would we end up including every person on earth in that construction?
    Last edited: May 19, 2007
  2. jcsd
  3. May 19, 2007 #2
    Maybe this has something to do with Ramsey numbers and the work of Erdos? However, maybe this is not a question of coloring lines red or green.

    Now if someone lived in the woods and his relatives and acquaintances in the city had all died, then no.
  4. May 19, 2007 #3
    you should be able to do it with dna but for one problem, if i remember correctly some parts of sequence are generated randomly. and i can see why that might be necessary, with a small genepool you'd need that to prevent clones.

    don't quote me on this.
  5. May 19, 2007 #4


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    Not likely at all.
  6. May 19, 2007 #5


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    You want to look up the Six Degrees of Kevin Bacon.
  7. May 19, 2007 #6


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    A programmer for a social networking website would be the person to ask about this. If you have a MySpace profile, for instance, have you ever seen a profile of another person that did not read "so and so is in your network."

    I'd be inclined to doubt this is possible, though. There have to some remote islanders or siberian reindeer herders somewhere out there that are not a part of your earth network.
  8. May 20, 2007 #7


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    Only because we don't have complete records and never will.

    I pondered something similar - starting with we have 2 parents, 4 grandparents, 8 great-grandparents, 16, 32, . . . basically in prvious generation there would be 2n. Ten generations ago, would be 1024 and 20 generations ago would be 1024*1024 or 1048576, and in 30 generations 1073741824 folks. If 1 generation is 25 years on average, then 10 generations is only 250 years ago, 20 generation encompasses 500 years, and 30 generations encompasses 750 years. But 750 years ago, there we not more than a billion people.

    The 2n does not take into account the intermixing within clan or tribe, i.e. reproduction within a geographically limited population, nor the separation of populations. Somewhere there was an article on an Irish king who is probably a common ancestor to several million Irish people. As others pointed out, there were migrations long ago and various popluations split off and evolved genetically different characteristics, but there may be no way of figuring out precisely when or where the divergences occurred.

    Recently I heard a discussion about humans as colonies of dissimilar organisms (cells). Within that discussion was mention of the differences in the DNA, and I think the implication was that DNA has been added to the human species from outside, i.e. human cells have more DNA than humans of thousands, or 10's or 100's of thousands of years ago - and not all DNA originated in humans. Interesting idea.
  9. May 20, 2007 #8


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    I've heard that no one on the planet is more than 50th cousins. I have never attempted to verify this. I've also heard that most people (in the US) are about 3 to 5 handshakes away from the presidentent of the USA. In other words, you know someone who knows someone who knows someone who knows the president. I questioned this right away until my mom pointed someone we knew who had a sibling married to a US senator.
  10. May 20, 2007 #9
    My girlfriend got to shake Bush Sr. and Clinton's hand at her graduation yesterday:bugeye:
  11. May 20, 2007 #10


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    Tribes in the Amazon and New Guinea have been recently found and there could be more undiscovered. So, while the number may be surprisingly high, it would never include the entire world population
  12. May 20, 2007 #11


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    That's my reasoning why this would be impossible as well. Perhaps connecting the members of "first world nations," or whatever the current politically correct term for that is, would be possible, especially given the internet and frequency of air travel, but when you start including people such as members of remote tribes living in the rainforest, you're going to have gaps.
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