Researchers have debated whether eukaryotes—the group of relatively complex organisms that includes fungi, plants, and animals—are descendants of archaea or merely their close relatives. Newly discovered archaea from the bottom of the North Atlantic Ocean suggest that eukaryotes evolved from archaea. A genomic analysis of one of the organisms, called Loki, reveals that it is the most eukaryotelike prokaryote so far discovered. The study suggests that the ancestor of eukaroytes might have had an actin cytoskeleton and rudimentary internal structures composed of membranes.

To read the full story, see the 8 May issue of Science.