On the universal tree of life, all eukaryotic life falls on exactly one branch. This suggests that eukaryotic cells originated only once, which is consistent with their origin being unlikely.

Whether the timeline of these molecules matches the timeline of organismal diversification, however, remains to be seen. "You could take different molecules and get a different topology," says Caetano ...

Archaea, hardy single-celled organisms that form the third domain at the top of the universal tree of life, have survived for billions of years in some of the most extreme environments on Earth.

On the universal tree of life, all eukaryotic life falls on exactly one branch. This suggests that eukaryotic cells originated only once, which is consistent with their origin being unlikely.

On the universal tree of life, all eukaryotic life falls on exactly one branch. This suggests that eukaryotic cells originated only once, which is consistent with their origin being unlikely.