Short as it is on the cosmic scale, history’s been a pretty long time. Nobody found wheat and started making bread the next day. It was an incredibly long process that probably started with soaking the grains they were eating to make them more palatable and easier to consume. Then somebody thought to heat the wet grains. Then someone decided to crush the grains and you had porridge or gruel. A few iterations later someone comes up with a simple unleavened bread. Naturally-occurring yeast and dough left alone for a few hours could probably lead to rudimentary rising dough from there, and eventually we have brioche and marble rye.