Don't be silly, cavemen didn't exist
This is proven by the Flintstones, in which they have conquered the use of wheels and stones, but this happened before the stone age therefore must be incorrect. If you disagree with this then see the general answer to anything which makes belief in God difficult.*
*God put neanderthals on the planet underground so that we could find them (by His Almighty choice) to test us in our belief, if we don't believe then we will go to hell. If this isn't a good enough answer then see the second method.**
**The bible is not a fundamental reflection on how the world was created, Adam and Eve are just metaphors for the creation of the planet Earth. Any questions on this simply show a lack of understanding, therefore don't question Him. If this isn't a good enough answer, please see the third method.***
***God knows best.