Genesis 1:26-28
Then God said, "Let us make man in our image, in our likeness, and let them rule over the fish of the sea and the birds of the air, over the livestock, over all the earth, and over all the creatures that move along the ground." So God created man in his own image, in the image of God he created him; male and female he created them.
God blessed them and said to them, "Be fruitful and increase in number; fill the earth and subdue it. Rule over the fish of the sea and the birds of the air and over every living creature that moves on the ground."
Genesis 2:7
the LORD God formed the man from the dust of the ground and breathed into his nostrils the breath of life, and the man became a living being.
Genesis 2:18-20
The LORD God said, "It is not good for the man to be alone. I will make a helper suitable for him." Now the LORD God had formed out of the ground all the beasts of the field and all the birds of the air. He brought them to the man to see what he would name them; and whatever the man called each living creature, that was its name. So the man gave names to all the livestock, the birds of the air and all the beasts of the field.
If you look in Genesis 1, mankind, male and female, were created at the same time animals were. In Genesis 2, Adam was created before animals were. It is conceivable to believe that Adam and Eve's children married people from other villages, people that God created at the same time He created the animals, fish and birds, and did not breed within the bloodline.
Yours in Christ,
Jen