Thread: Backtracking Family Tree

Hi guys.

Got quite an interesting thing puzzling me.. (i think it's interesting anyway)

Ok.. I have 2 parents, each of my parents had 2 parents. My grandparents had 2 parents and so on...

After 30 (or so) generations of doing this, you end up with more people than there were in the world at that time.

Basically i'm a bit puzzled by the whole thing, is this an age old quesiton of "chicken or egg"? is it something that has been asked by many? Are there theories around this? if so, what's the name of the theory?

Cheers

-Nonameo-

What's your question exactly? As you go farther back in generations the number of ancestors any given individual has increases. I'm not sure what you're using the number of people in the world during that generation's time for. Guess I'm just missing your point.

:? people don't double every generation.. more like gain 1,1 every generation.

plus i guess you didn't really make up a question... like neutrino said...

Sorry, i guess i didnt really make my point very clear.

Basically i'm working backwards. It's like researching a family tree.. Everyone had 2 parents in order for them to be alive.. i think this is granted. So every generation back you go, you have to double the number.

i.e.

Me
2 Parents
4 Grandparents
8 Great Grandparents
16 Great Great Grandparents
and so on..

after aprox 33 generations back (let's say 900 years ago) you end up with about 4 Billion people. You clearly cannot go back any further as that would be impossible, you'd have more people than exsisted on the planet.

I want to just put this theory to you guys, maybe my logic is flawed, maybe it's an unanswerable question.

If you can only go back 900 years before you hit this problem then there must be something i'm missing, as we know our race goes MUCH further back than this.

It's hard for me to think of a specific question regarding this topic, i just want you guys to think about it and hopefully shed some light on it.

Any thoughts?

-Nonameo-

I think I get what you're asking. You want to know why the population is greater now than it used to be even though if you go back from yourself the numbers seem to increase...right?

If that's what you're asking I'd assume it's because more people are having more kids, less people are dying from diseases and people are living longer.

The U.S. average fertility rate is currently 2.1335 births per woman. It only takes 2 people to make a baby. So after 2 kids the population is growing.

Originally Posted by Nonameo

It's hard for me to think of a specific question regarding this topic, i just want you guys to think about it and hopefully shed some light on it.

Any thoughts?

Your problem comes from you thinking that all of your ancestors are unrelated to each other. It is commonly thought, I believe, that most people in the world are related to each other, and you have a great deal of genetic commonality among your ancestors. In other words, you cannot just do the math for 100 generations and come up with 2^100, as most people will appear multiple times in that interval. For example, your ancestor 30 generations back through your father can be the same person as your ancestor 30 generations back through another branch of your family.

Hermes i think you got it. That does make sense. So there are a lot of relations further back which stops the doubling.

Cheers Hermes, that one was starting to bug me.

Thanks again

-Nonameo-