Counterintuitive as it seems to many, computer models have shown that, with a very high probability, the last common ancestor of all living humans has lived surprisingly recently, maybe as little as 3500 years ago. More recently, genomic testing has helped to validate some of the assumptions underlying these models, showing that a pair of randomly picked individuals from e.g. Hungary and UK share about five *genetic* ancestors as little as ~1000 years back, with translates readily to thousands, if not millions of shared genealogical ancestors.
What I’m doing here is to make an even more minimalistic model: One that does without explicitly modeling large-scale migrations. Instead, all I model is admixture between neighbouring villages. And even with such an impoverished model, pretty much everyone shares ancestors by around generation 160.