I think it's interesting that the author writes extensively here about the relationship between hierarchical rank and income without mentioning the actual trait that most reliably predicts the ascension of hierarchies: ambition.

I've written about this trait before (1) and was expecting it to be explored with the mention of "trait" in the title (which typically refers to temperament or personality). More ambitious people consistently pursue roles that beget status, authority, and income opportunity. Ambition, which is a combination of traits in itself, reliably predicts actual outcomes like educational achievement, the pursuit of more prestigious occupations, career advancement, work output (per the author's mention of working full time vs part time), etc. While the research on ambition is admittedly fragmentary, it's safe to say there is more than purely an economic angle to this conversation.

(1) https://www.bringambition.com/post/what-is-ambition ; https://www.bringambition.com/post/history-of-ambition