Aristotle cast older brothers as ethical coaches for younger ones
A brother is a male sibling sharing one or more parents—a first-degree relative when full. English inherits Proto-Indo-European *bʰréh₂tēr via Latin frater. Aristotle's Nicomachean Ethics (350 BCE) likens brotherly friendship to comradeship among equals close in age and upbringing.
The plural can be brothers or brethren, and the female counterpart is a sister. The term covers any boy or man who shares at least one parent with another person, and a full brother counts as a first-degree relative. Outside the family, people also apply the word affectionately to men who are not related to them at all.
Studies of siblings turn up some surprising effects. Among pairs of brothers, warmer relationships go with more risk-taking, a link not found in sister or mixed pairs, and nobody yet knows why. The finding implies that while conflict between siblings raises the chance of risky behaviour, affection offers no protection against it. Some studies report that girls with an older brother reach menarche about a year later, and other work finds that a man's likelihood of being gay rises with the number of older brothers he has.
In Book VIII of the Nicomachean Ethics, written around 350 BCE, Aristotle argues that brothers come to resemble each other in character because they share parents, upbringing and schooling, and that their bond has withstood time better than any other. From this he draws a duty for the elder: to act well so that the younger learns goodness by copying him. The younger boy gradually takes on those habits and grows to resemble his brother. Habits of virtue or vice, Aristotle warns, are hard to break once rooted, so the example set early tends to last a lifetime.
Source: Brother
