But what difference, other than the sentimentality of blood ties, is there between brothers sharing material nonpublic information and friends doing the same? Does a favor for a sibling involve “at least a potential gain of a pecuniary or similarly valuable nature,” while one for a friend does not? Aren’t we genetically predisposed to be altruistic with kin – which, one would think, makes favors between siblings less liable to personally benefit one or the other?
http://dealbreaker.com/2016/12/supreme-court-puts-price-brothers-love/