A plausible theory as to why this can happen.

Apparently, millions of people (10% in a large region and 0.5% globally) are direct descendants of Genghis Khan, one of the worlds greatest conquerors - and also one of the most prolific breeders[1].

“Lots of men have lots of sons, by chance. But what normally doesn’t happen is the sons have a high probability of having lots of sons themselves. You have to have a reinforcing effect[1]”. You need to have a prolific breeder spread out over a large geographic area whose sons are also more likely to have many kids.

Maybe 8,000 years ago something similar happened.

[1]https://www.nature.com/news/genghis-khan-s-genetic-legacy-ha...