A Christian is someone who has accepted Jesus Christ as his (or her) savior, based on what the Bible teaches.  Jesus explains further:

If a man love me, he will keep my words: and my Father will love him, and we will come unto him, and make our abode with him.  He that loveth me not keepeth not my sayings: and the word which ye hear is not mine, but the Father's which sent me. (John 14: 23-24)

So, if you don't believe God's words, then don't claim to be a Christian.  If you believe in molecules-to-man evolution, then you don't believe God's words, because there is ample evidence from the Bible that God created the world (including man) in 6 days.

  • Exodus 20:11 says "for in 6 days the Lord made heaven and earth, the sea and all that in them is."

  • Genesis says the first day, the third day, etc... not "the first billion years."

  • God did say the word year in Genesis 1:14 when he said, "Let there be lights in the firmament of the heaven to divide the day from the night; and let them be for signs, and for seasons, and for days, and years"... but every reference to the defining time units of the creation uses the word day.  So clearly God knew that he meant day when he said it, because he used a different word altogether when he wanted to say years.

  • God created the plants on day 3.  If those days were actually years long, those plant would have had a pretty hard time waiting years for the sun to come up on day 4, and then surviving without pollination for years until day 6 when the insects were created.

  • Every creature, plant, and also man was created, which means "to bring into existence."  That is distinctly different from "to change from one form to another."

  • The Bible says that death came by sin, that the death we all must face (unless we accept God's sacrifice, Jesus, as Savior) is the result of Adam's sin.  So there was no death, indeed nothing could have died, before Adam sinned in Genesis 3.  And God said in Genesis 1:31 that everything was "very good."  So there could not have been billions of years, and a pre-Adamite rebellion, and all kinds of death, between Genesis 1 and 2, because then it most certainly would not have been "very good."