The bacteria that make Gruyère, Emmental, and Sbrinz cheese — Streptococcus thermophilus, Lactobacillus delbrueckii, Lactobacillus helveticus — were domesticated 3,200 to 7,800 years ago. Molecular clock dating places their divergence from wild relatives squarely in the archaeological window of early cheesemaking in the Fertile Crescent and Swiss Alps.
Humans domesticated these bacteria before knowing bacteria existed.
The genomic signatures are indistinguishable from deliberate artificial selection. Reduced genetic diversity (0.02-0.11% polymorphic sites). Massive genome decay: 45% of pseudogenes result from transposon insertions. Metabolic collapse: S. thermophilus can use only 5 of 92 tested carbon sources, a 58% reduction from its wild ancestor. The bacteria lost their ability to survive anywhere except milk.
Yet 50 years of weekly quality measurements show the cultures produce remarkably consistent cheese. The bacteria are genetically deteriorating but functionally stable. Genes are breaking. The cheese tastes the same.
The explanation: the lost genes encode functions that were essential in the wild (surviving on diverse nutrients, resisting environmental stressors, competing with other microbes) but irrelevant in the dairy environment, where nutrient supply is unlimited, temperature is controlled, and competitors are excluded. Domestication stripped the genome to its dairy-essential minimum and continues stripping it. The bacteria are on an irreversible path toward minimal genomes — a trajectory that will eventually hit essential genes and cause functional failure, but hasn't yet.
The through-claim: an organism can be domesticated by accident, through nothing more than consistent environmental selection over thousands of years. The selector doesn't need to know the selectee exists. And the domestication signature — genomic decay, niche restriction, functional consistency — is the same whether the selection was intentional or not. The cheese made the bacteria, not the other way around.