Adam and Eve
One of the key questions when considering the different Creation and Evolution models is: were Adam and Eve literally the first humans, such that everyone has descended from them?
Adam is described as the first man in the Old and New Testaments of the Bible.
1 Corinthians15:45 "So it is written: "The first man Adam became a living being"; the last Adam [referring to Jesus], a life-giving spirit." (brackets added).
Eve is named as the mother of all mankind, Genesis 3:20 "Adam named his wife Eve, because she would become the mother of all the living."
The Hebrew for man (adam) sounds like and may be related to the Hebrew for ground (adamah) see Genesis 2:7. Sometimes in the Bible Adam refers to all mankind, but in other places Adam refers to an individual, the father of all mankind.
There are 17 references to Adam as an individual outside Genesis often associated with the Fall of Mankind, sin and death.
Romans 5:12, 15- 17 "Therefore, just as sin entered the world through one man, and death through sin, and in this way death came to all men, because all sinned. And what a difference between our sin and God’s generous gift of forgiveness. For this one man, Adam, brought death to many through his sin. But this other man, Jesus Christ, brought forgiveness to many through God’s bountiful gift. And the result of God’s gracious gift is very different from the result of that one man’s sin. For Adam’s sin led to condemnation, but we have the free gift of being accepted by God, even though we are guilty of many sins. The sin of this one man, Adam, caused death to rule over us, but all who receive God’s wonderful, gracious gift of righteousness will live in triumph over sin and death through this one man, Jesus Christ."
This and others are key texts for followers of Jesus. Believing that there was not a literal first man and woman does pose some theological difficulties. For example, Jesus is referred to as the second Adam - how can this be true if there wasn't a first Adam?
If Adam is only figurative, then what are we to make of the detailed biblical genealogies? Are some people figurative and others literal? (see Luke 3:23-38)
A commonly asked question is where did Cain get his wife from? If Adam and Eve were the first humans and they had a son called Cain, whom did he marry? The answer is simply that Adam and Eve had other sons and daughters, so Cain probably married his sister (or niece). This sounds shocking and unpalatable by todays standards and would clearly be unlawful in our society, but interestingly most of our laws have their foundation in the Bible. On this issue of marrying a close relative, it was around 2,500 years later that God gave Moses various laws about sexual relations, including various ones forbidding marriage to a close relation. Hence, it was not unlawful in the early days of mankind and, in fact, was the only option. The following article has a lot more information: Cain's Wife