One of the universal questions for a scientist who is a Christian is:  Was Adam the first man?

Of course not. (My opinion)  He was the first man created in the image of God.  We can date Adam to about 6000 years or so ago from the genealogies in the first books of the Bible.  Some religious people want to say that was the beginning of all life. But strata shows us bones of humanoids that date much further back than that--as well as the fish, birds and dinosauric species.  Earth is very old.  The Bible doesn't discuss that.

One of the few verses that tell us what happened on earth after sin entered the garden where Adam and Eve were, is when Cain begged God to put a mark on him so that the people "Out There" wouldn't kill him.  Who were those people?  They weren't in the garden of Eden with Adam and Eve.   Cain took a wife from the land of Nod.  Who was she?  Who lived in the land of Nod.  Cain knew about them and was afraid of them.   God doesn't say.

My son Scott suggested that we do know that Lucifer was removed from heaven because he tried to overthrow God.  He was damned to earth--where the Bible calls him the "Prince of the power of the air."  Many angels who supported Lucifer were kicked out along with him.  Could they reproduce?  That is a wild speculation.  We have no knowledge of that.  I'm not going to speculate, but will say that a few years later, "...the sons of God saw the daughters of men that they were fair and they took them wives..."  It sounds like two groups of people.  1. Sons of God, 2. Daughters of men.  "...and it repented the Lord that he had made man on the earth, and it grieved him at his heart..."