Genesis gives us two descriptions of creating man.
This is the first:
Genesis 1:27 So God created mankind in his own image, in the image of God he
created them; male and female he created them. 28 God blessed them and
said to them, “Be fruitful and increase in number;
So God created man and woman, release them to the world, and told them to procreate.
The second description is the story of Adam and Eve - they were put in Eden and there was no mention about procreation. Only after eating the forbidden fruit, God is talking about the pain of giving birth:
Genesis 3:16 To the woman he said, "I will greatly increase your pangs in childbearing; > in pain you shall bring forth children, yet your desire shall be for your husband, and
he shall rule over you."
Base on these descriptions Adam and Eve may not be the first human creatures on earth. Their children could procreate with descendants of people from the first creation.