I recently read Francis Galton's Hereditary Genius (1869), in which he argues that genius, as measured by eminent reputation, is hereditary (could you have guessed?). Anyway, his method, once he has established his principles for defining eminence, is to explore professions, especially reasonably well-documented ones like judges, statesmen, commanders, writers, artists, divines, "men of science," poets, and musicians.
In each field, he argues, there is an over-representation of related eminent individuals - fathers and sons, brothers, cousins, etc - indicating that genius is hereditary. The arguments are tremendously flawed, as Galton dismisses all sorts of social factors, working under the assumption that quality will out. He discounts the idea of "eminent women" entirely, although does make some observations on the importance of women in transmitting all that genius. And while men from other nations and races may be eminent, there just aren't as many of them as there are of the Anglo-Saxon sort (who, admittedly, lag behind the ancient Athenians in the ratio of geniuses to regular folk). It's an interesting bit of proto-eugenic writing from the man who coined the term, and one could argue that Galton had a vested interest, being cousin to Charles Darwin and all (I can imagine him thinking "My cousin's a genius - maybe I am too!").
He does say in his introduction to his second edition that he regrets using the word "genius" to represent the quality shared by these men, in favour of "talent," which is fair enough - he does seem to be writing more about individuals who are extremely talented... although in some cases this is difficult to judge (as in the case of the judges - Galton has a greater respect for their innate capacities than many of his contemporaries).
Interestingly, he links intellectual strength and vigour with physical strength, especially in his section on oarsmen. Of course, they're all going to Oxford and Cambridge to begin with.... so at least they're well-fed.