Defense system common to all life came from 'Asgard'

Defense systems found in all complex life on Earth came from "Asgard."

The ancestor of plants, Animals and fungi evolved around 2 billion years ago, likely from a group of complex microbes called Asgard archaea — and we inherited two defense proteins that fight off viruses from those single-cell organisms, new research suggests.

"This study shows that if we want to understand the origins of our immune system, we need to include archaea, especially Asgard archaea, in the discussion," study first author Pedro Lopes Leão, a microbiologist at Radboud University in the Netherlands, told Live Science in an email.

The tree of life is broken up into three domains: Bacteria, Eukarya and Archaea. Bacteria are tiny, simple cells with no nucleus. Eukaryotes, by contrast, keep their DNA in a nucleus and have specialized "organelles," such as mitochondria and ribosomes, each of which performs specific functions. And then there are the microscopic-yet-complex archaea, which lack nuclei and organelles, but use energy in ways similar to eukaryotes.

"These microbes are super interesting because they are more like plants and Animals (eukaryotes) than bacteria," senior study author Brett Baker, an associate professor of integrative biology and marine Science at the University of Texas at Austin, told Live Science in an email.

Related: Meet LUCA, the 4.2 billion-year-old cell that's the ancestor of all life on Earth today

In 2015, scientists first described a newfound superfamily of archaea that bridged the gap between bacteria and eukaryotes. Named Asgard archaea because they were collected from a deep-sea hydrothermal vent in the Arctic known as "Loki's castle," these cells transformed our understanding of the evolution of complex life.