Niccolò Machiavelli
Discourses on the First Decade of Titus Livius (Chap. 3.46) (English version)
How the Characteristics of Families come to be perpetuated.

Manners and institutions differing in different cities, seem here to produce a harder and there a softer race; and a like difference may also be discerned in the character of different families in the same city. And while this holds good of all cities, we have many instances of it in reading the history of Rome. For we find the Manlii always stern and stubborn; the Valerii kindly and courteous; the Claudii haughty and ambitious; and many families besides similarly distinguished from one another by their peculiar qualities.

These qualities we cannot refer wholly to the blood, for that must change as a result of repeated intermarriages, but must ascribe rather to the different training and education given in different families. For much turns on whether a child of tender years hears a thing well or ill spoken of, since this must needs make an impression on him whereby his whole conduct in after life will be influenced. Were it otherwise we should not have found the whole family of the Claudii moved by the desires and stirred by the passions which Titus Livius notes in many of them, and more especially in one holding the office of censor, who, when his colleague laid down his magistracy, as the law prescribed, at the end of eighteen months, would not resign, maintaining that he was entitled to hold the office for five years in accordance with the original law by which the censorship was regulated. And although his refusal gave occasion to much controversy, and bred great tumult and disturbance, no means could be found to depose him from his office, which he persisted in retaining in opposition to the will of the entire commons and a majority of the senate. And any who shall read the speech made against him by Publius Sempronius, tribune of the people, will find therein all the Claudian insolence exposed, and will recognize the docility and good temper shown by the body of the citizens in respecting the laws and institutions of their country.