a customary descent of lands or tenements, in certain places, by which they descend to the youngest instead of the eldest son; or, if the owner have no issue, to the younger instead of the elder brother. This custom goes with the land, although there be a devise or feoffment at the common law to the contrary. The reason of this custom, says Littleton, is, because the youngest is presumed in law to be least able to provide for himself.