I don't even know if this is 'genetic' as much as it is the change in diet and lifestyle changing the way our bones and teeth develop.
For instance, if at birth we dropped an infant in a culture that rarely cooked and didn't eat farmed food, maybe the jaws and teeth would develop to match the 'old' human structure.
Well, probably not, at least not for many generations. It's like the farmer who selects sheep for twinning (an uncommon thing in nature, but very common now in sheep)--eventually, if sheep are left alone in the wild, twinning will almost disappear. However, we've also bred most sheep not to be able to shed their fleece, so those sheep in the wild would smother before they could stop twinning.