A rejuvenation period that takes place after an embryo has attached to the uterus sets the growing embryo at its youngest biological age, dubbed “ground zero,” researchers report June 25 in Science Advances. Both mouse and human germline cells appear to reset their biological age in the early stages of an embryo’s development.

In a new study, scientists describe evidence that supports that rejuvenation hypothesis. So researchers have hypothesized that germline cells might instead reset their age after conception, reversing any damage. But studies have shown signs of aging in eggs and sperm, dispelling that idea. “For some reason, you are at zero.”Įxperts once thought that germline cells might be ageless - somehow protected from the passage of time ( SN: 3/10/04). “When you are born, you don’t inherit your parents’ age,” says Yukiko Yamashita, a developmental biologist at MIT who studies the immortality of germline cells such as eggs or sperm.

But why our offspring don’t inherit those changes - effectively aging a child even before birth - has been a mystery. As people age, so do all of our cells, which accumulate damage over time.