Not by bread alone. But 20% by bread.

From What 3,000-Year-Old Egyptian Wheat Tells Us About the Genetics of Bread by Michael Scott.

Human societies need food – and that often means wheat, which was first cultivated more than 12,000 years ago. Today, around one in five calories consumed by humans is from wheat. Over this time, humans have moved wheat species around the globe and transformed them through cultivation and breeding.

Most wheat species have a hybrid origin. Their DNA has also revealed a complex history of further hybridisation, with modern varieties carrying large genomic chunks that originate from related species. In some cases, genetic material was probably exchanged between species in the fields of early farmers. In other cases, modern breeders have made interspecies crosses deliberately in order to introduce useful genetic variation, such as disease resistance.

Ancient DNA, taken directly from bioarchaeological specimens, is particularly valuable for tracking changes through time, allowing us to uncover lost variation and to link specific time points with genetic footprints of crop movement and breeding. We recently sequenced the genome of a 3,000-year-old sample of Egyptian emmer wheat, and comparisons with modern samples suggest a story of how that crop spread from one region to others.