Contrary to the statements of most evolutionary writers, few (if any) creationists have ever advocated the idea of absolute fixity of species. The Biblical unit of biological taxonomy, of course, is the Genesis "kind" (Hebrew, min).

It may be worth mentioning that this fact was stressed in my first book on creationism some 55 years ago:

"Turn not to the right hand nor to the left: remove thy foot from evil" (Proverbs 4:27).

"For the wisdom of this world is foolishness with God. For it is written, He taketh the wise in their own craftiness" (I Corinthians 3:19).

"For our light affliction, which is but for a moment, worketh for us a far more exceeding and eternal weight of glory" (II Corinthians 4:17).

"Knowing that Christ being raised from the dead dieth no more;
death hath no more dominion over Him" (Romans 6:9).