Adam and Eve were not the first born male and female.
They were created.
Cain was the first born.
Genesis 2:7, 22 (KJV) – and the Lord God formed man of the dust of the ground, and breathed into his nostrils the breath of life; and man became a living soul. And the rib, which the Lord God had taken from man, made he a woman, and brought her unto the man.