According to the Bible, Adam and Eve, the two first people (Genesis 2), initially had two sons, Cain and Abel (Genesis 4:1-2). Cain murdered his brother Abel (Genesis 4:8), took off into the Land of Nod (Genesis 4:16), and had many descendants (Genesis 4:17-24). We aren't told specifically who his wife was.
We are told, however, that Adam (and probably Eve also) lived for approximately one thousand years (Genesis 5:5), and that after Cain and Abel they had several sons and daughters (Genesis 5:4). It seems most likely, therefore, that Cain married one of his sisters.
It seems possible that incest was not formally outlawed by God until the time of Moses (Leviticus 18:9), approximately 2,500 years after creation. Initially, with the entire human race descending from two parents and a command given by God to go forth and multiply (Genesis 1:28, 9:1), incest would not only have been permitted, but necessary.
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Genesis 2:4 begins the section, stating that the following events describe the creation of the world.
Genesis 2:5 claims that at this point, there had been no rain, there had been no vegetation, and there was no man. Genesis 2:7 says God then created a man out of dirt and gave him the breath of life, so this would appear to be the first man.
Genesis 2:20 states that there was no helper for this man that was comparable to him, and since only newly-created animals are available for consideration at this point, it appears no women or other men exist yet. So, in Genesis 2:22, a woman is created out of his rib to be his helper.
Per Genesis 2, these appear to be the first two people.
Do you have an alternate perspective that you think is clear from the text?