Most nations are mixed because of intermarriage. In view of most humans, few would be able to identify who they are. However through DNA testing, a number of people’s origin has been found. Some Kohanim have been identified through DNA. Would it be right to say that irrespective of mixed marriages, Hashem knows the origin of every man? In this case He would be able to say which family, I.e Shemite, Chamite or from Yefet right down to the family?
Even though God knows everything, it may very well be His desire for man not to know, and even beneficial for the nations of the world to mix and forever intermarry in a way which will bring world peace, equality and cooperation. If the President of Russia had a granddaughter living in America, he would think many times before attacking! Being that all gentiles are meant to be Noachides regardless of whether they are from Shem, Cham or Yefet, and accordingly, their genealogy is irrelevant, I would doubt that any kind of DNA test should, and subsequently could, be found. For example, after mankind has advanced and thank God, freed the slaves in most countries, why should anyone (especially God) want us to know who exactly is from Canaan and should theoretically be enslaved!! Rav Kook stresses: our lack of knowledge and deficiency of this medical identification is undoubtedly God’s will. On the other hand, male Kohanim are unique and are meant to remain distinct. Accordingly God revealed to man their particular sex-linked gene which is passed down from father to son, exactly as the Kohanic sex-linked descent is determined (although it’s not halachically concrete, it can’t be a coincidence that this is by far the most consistent and accurate genetic mapping in mankind, which spans 3,300 years and all of the continents!). Similarly Israel, ‘the nation of priests (kohanim)” (Shmot 19, 6), is unique and distinct, and not meant to intermarry with gentiles. World brotherhood is meant to become like one big family, but even in a family, one needs a “firstborn” to set the tone, atmosphere and world culture among the brothers, when the Father (God) isn’t seen to be around: “My son, My firstborn, Israel” (ibid, 4, 22). Similarly, the Jewish national return to Israel is necessary to concentrate the Godly Bible values, without dilution or assimilation, to influence the world for the better, rather than be influenced.