Embryos appear to reverse their biological clock early in development

Amazing stuff!

"... [Scientists] once thought that germline cells might be ageless — somehow protected from the passage of time (SN: 3/10/04). But studies have shown signs of aging in eggs and sperm, dispelling that idea. ...

In a new study, scientists describe evidence that supports that rejuvenation hypothesis. Both mouse and human germline cells appear to reset their biological age in the early stages of an embryo’s development. 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.  ..."

"The notion that the germ line does not age goes back to the 19th-century ideas of August Weismann. However, being metabolically active, the germ line accumulates damage and other changes over time, i.e., it ages. ...
We further found that pluripotent stem cells do not age even after extensive passaging and that the examined epigenetic age dynamics is conserved across species. Overall, this study uncovers a natural rejuvenation event during embryogenesis and suggests that the minimal biological age (ground zero) marks the beginning of organismal aging."

Embryos appear to reverse their biological clock early in development | Science News In mice, a ‘rejuvenation event’ wipes out genetic signs of aging days after fertilization

Epigenetic clocks reveal a rejuvenation event during embryogenesis followed by aging