I've been thinking about this for a long time: God created Adam, and according to Darwin's evolutionary theory and natural selection, Adam could have been a monkey (Darwin's theory has come under attack lately, but for different reasons besides religious).
Islam, of course, forbids us to think of Adam (or Eve) as a primate, for various reasons, but mostly because animals and humans are different in the sense that humans have been granted free will. If Adam was a monkey (or the descendent of monkeys -- which is also impossible according to Quran since he was created a "man" before he was kicked out of heaven), then it would be difficult to reconcile the issue of free will.
â€œO mankind, be careful of your duty to your Lord, Who created you from a single soul, and from it created its mate, and from the two of them has spread forth a multitude of men and women.â€� (Al-Quran, Chapter 4, Verse 1)
â€œAll of you are Children of Adam, and Adam was created from dust.â€� (Prophet Muhammad, pbuh)
And yet, fossilized findings tends to show a gradual evolution of early man -- the cro-magnons, the neandertals, etc. There must be a reconciliation between what scientiests have found and what the Quran tells us, but i'm unsure what it is.
Looks like the thought i've given the subject is still incomplete. More research required.