Around 2000 B.C., a baker in the ancient Egyptian city of Thebes captured yeast from the air and kneaded it into a triangle of dough. Once baked, the bread was buried in a dedication ceremony beneath the temple of Pharaoh Mentuhotep II on the west bank of the Nile. There the yeast slept like a microbial mummy for four millennia, until 2019. That’s when Seamus Blackley—a physicist and game designer best known for creating the Xbox—suctioned it up with a syringe and revived it in a sourdough starter. Blackley, an amateur Egyptologist, often thinks about this ancient baker as he...