If the Creation story of Genesis isn't true-then why would you believe marriage is saanctioned by the Creator since it appears in the Creation story? (Theistic evolutionists are those who believe in evolution but claim that God did it)
Therefore shall a man leave his father and his mother, and shall cleave unto his
wife: and they shall be one flesh. And they were both naked, the man and his wife, and were not ashamed. Geenesis 2:24,25