Genesis twin (4)
I believe the answer is:
esau
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">genesis twin</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for esau that I've seen before include "First son of Isaac (Bible)" , "Hairy OT character" , "Old Testament twin" , "Birthright seller (Bible)" , "One of Isaac's sons" .)