Deuteronomy 25:5-6

If brethren dwell together In the same town, or, at least, country. For if the next brother had removed his habitation into remote parts, or were carried thither into captivity, then the wife of the dead had her liberty to marry the next kinsman that lived in the same place with her. One Any of them, for the words are general, and the reason of the law was to keep up the distinction of tribes and families, that so the Messiah might be discovered by the family from which he was appointed to proceed; and also of inheritances, which were divided among all the brethren, the firstborn having only a double portion. A stranger To one of another family. That his name be not put out That a family be not lost. So this was a provision that the number of their families might not be diminished.