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Smallpox was eradicated relatively quickly, but other diseases have proved harder to eliminate. The reasons are a mix of biology and psychology.
Kidneys sniff out signals from gut bacteria for cues to lower blood pressure after meals. Our understanding of how the symbiotic microbes affect health is becoming much more molecular.
Tiny lines laid down by tooth enamel appear to reveal a previously unknown biological rhythm. If confirmed, the finding could help researchers understand why big animals grow slower — and live longer — than small ones.