Korbie's hair was straightish, because it was too short, and the curls too delicate. If it was humid enough and you fluffed his hair while wet, he'd have the start of curls, but the daily laying down, petting and rubbing his head against stuff would straighten his hair. But the curls did come in eventually.
Here's my album to show you how dramatic his hair change was. Towards the bottom are some infant pictures that show how straight his hair was. Now he has the tightest little ringlets, those pictures are not good hair days for him.