From among all nations or from Abraham's seed?

In Surah 29:27 we read:

   And We bestowed on him Isaac and Jacob, 
   and We established the prophethood and the Scripture among his seed, 
   and We gave him his reward in the world, 
   and lo! in the Hereafter he verily is among the righteous.

Some debate whether "his seed" refers to Jacob as the last person mentioned or to Abraham (him) whom Isaac and Jacob were given to. In either case, the prophethood is stated to belong to Abraham's descendents.

If all prophets are from Abraham's seed as Surah 29:27 declares, it can hardly be possible that at the same time there are messengers from among every people:

   And verily We have raised among every people a messenger,
   (proclaiming): Serve Allah and shun false gods. ...
                                    Surah 16:36

Does anybody intend to claim that all people groups are physical descendants of Abraham?

And there are further problems with the prophets from Abraham's progeny.

Contradictions in the Qur'an
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