G Zhang

In a house where no one has done repairs for years, old junk doesn't just take up space. It starts to smell, shed dust, and spoil the air for everyone living there. Senescent cells behave much the same way in our bodies: they can no longer divide, but they reliably broadcast inflammatory signals around them, accelerating the aging of neighboring tissues.

The alfalfa root is studded with pink bumps the size of peas. Inside each one, bacteria turn nitrogen from the air into fertilizer, and the plant pays them back in sugar. To keep the deal from falling apart, the partners exchange protein messages, but until recently this conversation was almost inaudible to us.