Like many things here though there's a chicken and egg type scenario. Society mostly started with increasingly isolated tribal groups. Over time, and lots of killing, the most successful groups started to form into larger and larger groups. And the most successful individuals among these most successful groups were in turn on top of the top. At some point leadership implied what was an extremely high probability of a genetic advantage. And that advantage can persist through the centuries. It can also deteriorate.
A great example of this is the House of Habsburg. [1] They were one of the most powerful families in history completely dominating Europe politics with lineages of kings and emperors throughout the entire continent for some 5 centuries, including holding the throne of the Holy Roman Empire for more than 300 years. But the reason they're an interesting example is because they're also the namesake of the Habsburg Jaw - a genetic deformity that was greatly exaggerated in the family through the years due to excessive inbreeding. If you've seen a cartoon depiction of royalty they often are drawn with the extreme protruding chin, which is a reference to this deformity and family in particular.
That family was almost certainly extremely genetically fit at one point. But through excessive inbreeding they destroyed their own genetic lineage. In Spain this was especially pronounced with Charles II. [2] He was described as "short, lame, epileptic, senile, and bald before 35." He learned to talk at age 4, walk at 8. His Habsburg Jaw was so extreme he could not chew his own food. He, unsurprisingly, died childless at the age of 35 - ending 200 years of Habsburg rule in Spain. And to emphasize -- this is just one example. This family did not just rule Spain. They had lasting dynasties in Germany, Hungary, Croatia, England, Boehmia, Ireland, Portugal, and many other nations.
Only the male line died out. The Habsburg-Lorraine cadet branch took over and although they don't actually rule any countries since WWI, they are still quite wealthy and well-connected.
A great example of this is the House of Habsburg. [1] They were one of the most powerful families in history completely dominating Europe politics with lineages of kings and emperors throughout the entire continent for some 5 centuries, including holding the throne of the Holy Roman Empire for more than 300 years. But the reason they're an interesting example is because they're also the namesake of the Habsburg Jaw - a genetic deformity that was greatly exaggerated in the family through the years due to excessive inbreeding. If you've seen a cartoon depiction of royalty they often are drawn with the extreme protruding chin, which is a reference to this deformity and family in particular.
That family was almost certainly extremely genetically fit at one point. But through excessive inbreeding they destroyed their own genetic lineage. In Spain this was especially pronounced with Charles II. [2] He was described as "short, lame, epileptic, senile, and bald before 35." He learned to talk at age 4, walk at 8. His Habsburg Jaw was so extreme he could not chew his own food. He, unsurprisingly, died childless at the age of 35 - ending 200 years of Habsburg rule in Spain. And to emphasize -- this is just one example. This family did not just rule Spain. They had lasting dynasties in Germany, Hungary, Croatia, England, Boehmia, Ireland, Portugal, and many other nations.
Today, the entire house of Habsburg is extinct.
[1] - https://en.wikipedia.org/wiki/House_of_Habsburg
[2] - https://en.wikipedia.org/wiki/Charles_II_of_Spain