Primogeniture is the right, by law or custom, of the legitimate, firstborn son to inherit his parent's entire or main estate, in preference to daughters, elder illegitimate sons, younger sons and collateral relatives. The son of a deceased elder brother inherits before a living younger brother by right of substitution for the deceased heir. In the absence of any children, brothers succeed, individually, to the inheritance by seniority of age (subject to substitution). Among siblings, sons inherit before daughters. In the absence of male descendants in the male-line, there are variations of primogeniture which allocate the inheritance to a daughter or a brother or, in the absence of either, to another collateral relative, in a specified order (e.g. male-preference primogeniture, Salic primogeniture, semi-Salic primogeniture).