Pure religious BS. It doesn't work like that.
The further back you go, the less likely a person has descendents living today. Same thing for our future: Everyone living on Earth in 10,000 years will be the decendents of only a handful of people alive today. That's natural selection. Not everyone's offspring prosper, or dominate, even if you're famous like Mohammad or Jesus. On the other hand those two people may have many living descendents, in the parts of the world where they lived. They only lived a couple thousand years ago.