"For this reason Adam was created as a single person, to teach you that anyone who destroys one soul is described in Scripture as if he destroyed an entire world, and anyone who sustains one soul is described in Scripture as if he sustained an entire world... And to declare the greatness of the Holy One, praised be He, for a person uses a mold to cast a number of coins, and they are all similar to each other, while the Sovereign of all sovereigns, the Holy One, praised be He, cast each person in the mold of the first human being and none of them is similar to any other. Therefore each and every person must say: "For me the world was created". 

Sanhedrin 4:5