Mathematically, once you get your ancestors lined up, going back so many generations (I forget the number but it isn't that many - we are ALL, every man, woman and child on earth, genetically related.
If you have your genealogy traced back far enough, you will see that it's shaped in a diamond pattern, starting with you at the bottom and building up with your 2 parents, 4 grandparents, 8 great greats - etc. After some generations, you will start finding the same sets of great great 12-plus generations back, turning up in the generation more than once.
For example, I have 5 lines going back the Gov. Wm. Bradford of the Mayflower. He is my 7th great grandfather, 10 generations from me. In that generation, we all have thousands of great great couples. (Took a lot of people to make you!)
AS the marriages in the same areas come down through the lines, you will find people from the same lines marrying - cousins many generations removed - but leading back to a common ancestor.
The further back you go, the more the duplication as the numbers of separate couple begin to fold the actual numbers of separate couples back - until you reach to top of the diamond shape with ONE person sitting there.
So what does that say?
That we all evolved from the same baboon? /sarc
“EAch of us has the same number of ancestors.”
Huh?
You could belong to a society that encouraged marriage and childbearing as soon as someone enters puberty.
Alternatively, you could belong to a society that encouraged waiting until someone was in their thirties to have children.
Over time, the first society is going to be more populous and have a greater number of generations than the second.
Your logic (and I hesitate to use that word!) is faulty.