How accurate do you all think is the common ancestor theory?

sirleet

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Just wondering, how accurate do you guys think is the common ancestor theory? I'm sure many of you have heard of this, but for those who haven't, to sum it briefly, the theory states that all Europeans are descend from all of the Europeans 1000 years ago who had descendants. I'm kind of doubtful of this theory, but who knows.
(and a video states that all Europeans descend from Muhammed, because an Emir had a daughter in Spain, who converted to Christianity and was a refugee)

I just really don't know how me, being half Greek islander and Polish from two random villages, am descended from like some random Italian duke. But hey, it may be possible.
Just wondering, how accurate do you guys think is the common ancestor theory? I'm sure many of you have heard of this, but for those who haven't, to sum it briefly, the theory states that all Europeans are descend from all of the Europeans 1000 years ago who had descendants. I'm kind of doubtful of this theory, but who knows.
(and a video states that all Europeans descend from Muhammed, because an Emir had a daughter in Spain, who converted to Christianity and was a refugee)
 
Just wondering, how accurate do you guys think is the common ancestor theory? I'm sure many of you have heard of this, but for those who haven't, to sum it briefly, the theory states that all Europeans are descend from all of the Europeans 1000 years ago who had descendants. I'm kind of doubtful of this theory, but who knows.
(and a video states that all Europeans descend from Muhammed, because an Emir had a daughter in Spain, who converted to Christianity and was a refugee)

I just really don't know how me, being half Greek islander and Polish from two random villages, am descended from like some random Italian duke. But hey, it may be possible.
Just wondering, how accurate do you guys think is the common ancestor theory? I'm sure many of you have heard of this, but for those who haven't, to sum it briefly, the theory states that all Europeans are descend from all of the Europeans 1000 years ago who had descendants. I'm kind of doubtful of this theory, but who knows.
(and a video states that all Europeans descend from Muhammed, because an Emir had a daughter in Spain, who converted to Christianity and was a refugee)

Assuming 25 years per generation, there are about 40 generations in a thousand years. That's a lot of ancestors. Pedigree collapse has to be considered, but, still, we all have millions of ancestors from 1000 years ago. Many of those ancestors have millions, if not billions, of descendants.


Population of Ancestors
Years Ago

2 25
4 50
8 75
16 100
32 125
64 150
128 175
256
200
512 225
1,024 250
2,048 275
4,096
300
8,192 325
16,384 350
32,768 375
65,536 400
131,072 425
262,144 450
524,288 475
1,048,576 500
2,097,152 525
4,194,304 550
8,388,608 575
16,777,216 600
33,554,432 625
67,108,864 650
134,217,728 650
268,435,456 700
536,870,912 725
1,073,741,824 750
2,147,483,648 775
4,294,967,296 800
8,589,934,592 825
17,179,869,184 850
34,359,738,368
875
68,719,476,736 900
137,438,953,472
925
274,877,906,944
950
549,755,813,888
975
1,099,511,627,776 1000
 
The common ancestor theory is a mathematical model that depends on assumptions made about exogamy (marrying outside your village, if you like). If your village was so endogamous that no one ever married anyone from outside the village, then even after a thousand years all your ancestors would be from that village. However, if even a minority of marriages are with people from neighbouring villages, and that applies to all the neighbouring villages as well, then your ancestry can spread from village to village, and even from country to country, as you go back in time. Differences of language and religion might slow the spread, but the common ancestor theory is more plausible than the alternative, that no one married outside their village.

However, though we may be descended from millions of people who lived a thousand years ago, we have only inherited DNA from about 3,000 of those ancestors. That is because DNA is inherited in segments, and 40 generations ago the number of segments was 2,887. That's based on Reich's formula of number of segments = 47 + (71 x number of generations). So there's a big difference between genealogical ancestors and genetic ancestors. An Italian duke or a Scottish princess from a thousand years ago may be your ancestors, but it's very unlikely that you inherited any DNA from them.
 
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