Researchers analyzing ancient teeth from an Irish cave discovered significant changes in oral bacteria over 4,000 years. They found a decline in Streptococcus mutans, a bacteria linked to tooth decay, possibly due to its acidic nature hindering fossilization. The study suggests an increase in dental cavities with the advent of cereal agriculture, but a more pronounced rise with the introduction of sugary foods in recent centuries. This sheds light on historical shifts in oral microbiomes and their impact on human health.