As an attorney, I sometimes have the distasteful job of telling a client that they have no case. It really is not a happy thing. I could wish for every client to hit the jackpot, but I would be doing them no favors by allowing them to spend time and effort pursuing something which has no basis in the law.
So here, I must tell you that you probably should not pin your hopes of physical ancestry to one of the lost ten tribes of Israel on the use of “nivracheu” (aka nivrachu) in Genesis 12:3. The meaning you have been told, that it somehow references “mixing,” or “grafting in,” is spurious.
The Hebrew root is “barak,” which simply means “to bless.” In Hebrew, words are routinely modified to adapt to how they are used in a sentence. In this case, the letter “nun” is added to the front to make it a Niphal conjugation (passive or reflexive voice, depending on context), and that is further prefixed with a “vav,” which makes it a past perfect tense, or the idea of a done deal, what is sometimes called the “prophetic perfect tense,” speaking of a future event as though it were an accomplished fact.
In all of that, there is nothing remotely like a so-called “special” form of “barak” which doubles for “grafted in” or “mixed.” All you see in this passage is an ordinary, everyday Niphal conjugation of “to bless.” That’s just how you make words in Hebrew.
Now I am aware that some are claiming support for the “grafted” view from examples in various extrabiblical sources. All of these are asserting the possibility of an obscure alternative usage for the term. But in the samples typically used to promote the “grafted” view, Talmudic or otherwise, none of them turn out to be any good. Either the conjugation form is different, rendering the “pun” theory irrelevant, or an incorrect grouping of words is applied, or some other blatant mishandling of basic grammatical rules invalidates the alleged proof.
And one would have to wonder how the ordinary scribe of Israel would react to this hidden “mixing” concept, since so much else in the law emphasizes that mixing is bad. Using Moses as a template for spiritual realities per the book of Hebrews, one would have to conclude that God used mixing as a metaphor for impurity, idolatry, incompleteness of devotion to the pattern of worship established by God, and so forth. None of this would seem compatible with the idea of a blessing.
Furthermore, there appears to be evidence from the New Testament that such a meaning as biological mixing is quite impossible. Consider the following passage:
Gal 3:13-16 Christ hath redeemed us from the curse of the law, being made a curse for us: for it is written, Cursed is every one that hangeth on a tree: That the blessing of Abraham might come on the Gentiles through Jesus Christ; that we might receive the promise of the Spirit through faith. Brethren, I speak after the manner of men; Though it be but a man’s covenant, yet if it be confirmed, no man disannulleth, or addeth thereto. Now to Abraham and his seed were the promises made. He saith not, And to seeds, as of many; but as of one, And to thy seed, which is Christ.
Paul here seems to be saying that the blessing promised had a definite means of conveyance, faith in Christ. He further emphasizes that the blessing is not transmitted along a limitless number of separate biological lines (“seeds”), but is transmitted to whoever is found in Christ (“the seed”) through faith:
Gal 3:29 And if ye be Christ’s, then are ye Abraham’s seed, and heirs according to the promise.
Notice the order. First you belong to Christ, then you are Abraham’s seed, and an heir to the promise. Not the other way around.
Now Paul recognizes that even among humans, once a contract is set, you can’t add to it or take away from it. One of the ways people try to circumvent a contract is by attempting to “discover” an ambiguity from which they can extract some new meaning not intended by the original parties to the contract. And that is why contract law resists ambiguities. If there is an easy, obvious way to understand the plain sense of what the parties agreed to by taking the words at their face value, you’re not allowed to look for hidden or secondary meanings that radically alter that plain sense meaning. The judge won’t let you do that. I think that’s a good rule to apply here. “To bless” just means what it says, “to bless.”