Thus is the right answer, not "inheritability of intelligence". Economic status propagates through generations much more directly than any genetic quality like intelligence (which isn't even a quality commanded to a significant degree by genetics)
Economic status only lasts on average 3 generations.
> genetic quality like intelligence (which isn't even a quality commanded to a significant degree by genetics)
Actually quite the opposite. Intelligence is almost entirely genetic.
The reason you think economic status propagates is actually that intelligence propagates, and intelligence is strongly correlated with income.
Gregory Clark's work "The Som Also Rises", "A Farewell to Alms" and his various articles suggest the heritability of socioeconomic status is around 0.7 and is uniform across all human societies he and his team have studied. The upper class maintain their social status if not their wealth.
The same surnames that were over represented among Qing dynasty mandarins are over represented among upper level PRC officials. One in five Swedish prime ministers have had surnames indicative of noble ancestry when holders of said surnames are ~1% of the population.
Evidence?