I don't know the details, but it's fairly easy to imagine a series of small steps that could occur via random mutations, where each small step offered a slight fitness advantage over individuals without the mutation.

Isn't that just the definition of evolution?

It's a key problem many people have with understanding (and in some cases, believing) evolution. The classic example is the complex human eye.

Yes, which is why I took his comment to be slightly facetious.