Rabbinic Precautions

The source in the Torah for the laws of inheritance, is learned from the story of the daughters of Tzlofchad. A precedent was established that if someone has no son, then he is inherited by his daughter.

Torah law dictates that one is Jewish if his mother is Jewish. However, when it comes to determining whether someone is a Kohein, Levi, or Yisrael, it goes after the father. Similarly, it is determined that the tribe of affiliation, is also based on the father.
There is a clear difference in Jewish Law between a paternal son verses a maternal son. This applies to inheritance, and it also applies to the Mitzva of Yibum.

If a man dies childless, it is the responsibility of his paternal brother to take his wife in a levirate marriage. This obligation does not fall on a half brother that shares the same mother.

We also find this to be true when the Torah forbids marrying or having relations with one’s aunt. This applies to a father’s paternal brother’s wife, and not mother’s maternal or paternal’s brother’s wife, or even father’s maternal brother’s wife.

Because of this confusion, the Rabbis instituted certain prohibitions known as איסור מצוות or שניות. This latter term refers to secondary marriage relationships. These rabbinic decrees were meant to create a safeguard so that the Torah prohibitions would not be violated.

It could be that these laws have less relevance today, than in the time of the Talmud. Nevertheless, one gets a keen insight as to the intricate details of the Torah. If one would delve deeply into the study of the Torah, he would realize the Divine wisdom contained in it. Some of the laws involving inheritance and permissible marriages, are very complicated and detailed. One is rewarded for its studies as he becomes more and more in awe of the Torah that could only be written by Hashem, Himself.