Throughout the animal kingdom, mothers transfer microbes to their young while giving birth. Different species of tadpoles acquire specific skin bacteria from mother frogs even though they all live in the same pond with the same bacterial background. Emerging chicken eggs get inoculated with microbes from a bacteria-filled pouch near the mother hen’s rectum. And for millennia, mammalian babies have acquired founding populations of microbes by passing through their mothers’ vagina. This microbial handoff is also a critical aspect of infant health in humans. Today it is in peril.
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