Many people (not just creationists) hold the mistaken idea that evolution is supposed to happen in a straight line from single cells, through insects, reptiles, and ‘lower mammals’ and that we are the final product. This is based on an old, outdated idea of a ‘Great Chain of Being’. Evolution is not linear like this.
This has led to creationist errors, such as Michael Denton’s misunderstanding of protein sequences.
Evolution: What the Fossils Say and Why it Matters
Book by Donald R. Prothero.
Prothero explains this error in chapter 5.
Brief page on Berkeley's Understanding Evolution site.
1% of scientists get evolution wrong
Post by Adam Benton on his Filthy Monkey Men blog.
New Chinese hominins: A racist find – misguided mondays
Post by Adam Benton on his Filthy Monkey Men blog about a creationist considering evolution to be racist, based on the misconception of evolution as a 'ladder' rather than a branching bush.
Claim CB010.1: Even the simplest life is incredibly complex
Brief response in the Index to Creationist Claims in the TalkOrigins Archive to one common claim based on this misconception.