To a first approximation, yes. But it breaks apart quite quickly -> otherwise we'd the world pop would be much higher. thought experiment, if every rich family

To a first approximation, yes. But it breaks apart quite quickly -> otherwise we'd the world pop would be much higher. thought experiment, if every rich family in Flrnc had a million decedents, and there were (at least) a thousand families in Italy, then there would be a billion ppl in Italy today. What happens? Well first high child mortality, or death before reproduction. Then you send most of your daughters off to the nunnery. Your youngest son becomes the family priest. You marry within the group (actually not that dangerous, genetically). End result? The numbers stay low. Still many of us are probably related to these rich families. For example, otherwise normal, boss is related to the Eastern European royalty... through a courtesan. He didn't get squat from them (although he ironically ended up with their name by sheer coincidence).