Christians like Paul the Apostle, for instance.
If Adam was not the first man, Christian theology makes no sense. If he was an allegory, you're worshipping a Creator who is descended from a fictional character.
We are not given the names of those formed in Genesis 1:26. Where do you suppose the land of Nod was located wherein Cain found a wife? He had no sister yet, but he in short order found a mate.
This "The first man Adam was made a living soul;" was the first 'farmer' Genesis 2:5, and apparently it was already known the power of the devil to encourage, tempt us into sin, God already knew that this 'the first man Adam' would provide the blood line to Christ. Ever notice the control and care God Himself took to protect that blood line, in spite of what His children and the devil attempted to derail?
Hebrews 214 (also written by Paul) Forasmuch then as the children are partakers of flesh and blood, He also Himself likewise took part of the same; that through death He might destroy him that had the power of death, that is, the devil;
This death sentence of that first rebel took place before this flesh age began.
Those flesh bodies described in Genesis were given dominion over the fish of the sea, and over the fowl of the air, and over the cattle, and over all the earth, and every creeping thing that creepeth upon the earth."
It sometimes does amaze me that people believe that God was so unclear in Genesis 1:26 He then has Moses write a total different creation of the Adam and even had the Adam name the farm animals he was given. Course there is the millennium to teach what the majority have been mistaught.
DNA hard cold science demonstrates that not all God's children could have come from only two people, and Genesis does in fact describe two different days of creation of flesh bodies wherein their soul/spirit were placed in them to make them alive.