Carl Zimmer writes: None of us was made from scratch. Every human being develops from the fusion of two cells, an egg and a sperm, that are the descendants of other cells. The lineage of cells that joins one generation to the next — called the germline — is, in a sense, immortal.

Biologists have puzzled over the resilience of the germline for 130 years, but the phenomenon is still deeply mysterious.

Over time, a cell’s proteins become deformed and clump together. When cells divide, they pass that damage to their descendants. Over millions of years, the germline ought to become too devastated to produce healthy new life.

“You take humans — they age two, three or four decades, and then they have a baby that’s brand new,” said K. Adam Bohnert, a postdoctoral researcher at Calico Life Sciences in South San Francisco, Calif. “There’s some interesting biology there we just don’t understand.”

On Thursday in the journal Nature, Dr. Bohnert and Cynthia Kenyon, vice president for aging research at Calico, reported the discovery of one way in which the germline stays young.

Right before an egg is fertilized, it is swept clean of deformed proteins in a dramatic burst of housecleaning. [Continue reading…]