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:

How often have you tried to witness to someone only to be rebuffed by an inappropriate view of science as having disproved the Bible? "Evolution is true, the earth is billions of years old. Science has proved it. Thus the Bible can't be taken at face value. How could all those scientists be wrong?"