Raising an infant is an act of ecosystem engineering. You’re not just caring for a baby, but an entire world.

Right from birth, babies are colonised by legions of microbes that set up shop in their guts, skin, and more. These are vital. They help the growing human to digest its food, and to keep harmful microbes away. They are so important that newborns temporarily suppress their own immune system to give their microbial partners a chance to establish themselves.

Mum helps too. Her vaginal secretions provide her child with a starter pack of microbes. And her breast milk contains special sugars that seem to selectively nourish the gut bacteria that infants need.

Now, Eric Rogier from the University of