“As is my understanding,”
Heh. No, it isn’t.
“if Darwinism is true then there is no Christian God.”
Nope. No science has any room for the supernatural. Not to prove it, nor to disprove it. Noplace in the entire theory of evolution is it stated that there are no gods, whether creator gods like Ptah or Jehovah, or just interested bystanders like Thor, Aphrodite, Cupid.
“Common descent says everything started from one single organism.”
Well, not necessarily. COuld have been a number of organisms that shared genetic material. So we come from common ancestry, not necessarily a common ancestor.
“The Bible, however, says that God created all living creatures...”
WHich is not inconsistent with the theory of evolution.
“then Adam named them.”
Good LORD that must have been boring. “Hey! Hey! Wake up! Whaddaya call this?”
“It’s a beetle.”
“You didn’t even look! You called the last 500 beasts ‘beetle.’”
“Fine, it’s a horseshoe crabe.”
“What? Who told you about horseshoes? They haven’t been invented yet!”
“That theory is against God.”
No, it’s really not. The science couldn’t care any less about God, or the Bible, or Sunday School, or all those nurseries decorated with the cartoon ark and all the animals collected for the greatest genocidal event in literature.
YOU want to hold Genesis to be true. It can’t be literally true if evolution is true. Some people solve this dilemma by seeing Genesis as an allegory. Or a colorful metaphor. Or the ignorant writings of bronze-age idiots. Whatever works for you, it’s your problem.