Origins of Complex Life Uncovered in the Ocean Deep

Scientists have just discovered a missing link between two branches on the evolutionary tree of life hiding deep under the sea, one that we’ve been looking for since 1977.

Ever since microbiologist Carl Woese, the greatest scientist you’ve never heard of, added a third branch, archaea, to the existing two of prokaryotes (bacteria) and eukaryotes (which have more complex cells like our own), scientists have searched for the evolutionary connection between archaea and eukaryotes. While the reigning theory is that eukaryotes evolved from the simpler archaea, the ancestral parent of eukaryotes has remained elusive.

Scientists discovered the closest evolutionary relative to eukaryotic cells near a hydrothermal vent.

But just this week, a group of scientists announced that they found that connection buried under the Arctic Ocean near a hydrothermal vent called Loki’s Castle. They named it Lokiarchaeum, and published their findings in the journal Nature.

Here’s Carl Zimmer, reporting for the New York Times:

Analyzing the DNA, the researchers found that Lokiarchaeum is far more closely related to eukaryotes than any other known species of archaea. But even more surprising was that it had genes for many traits only found before in eukaryotes.

Among these genes were many that build special compartments inside eukaryote cells. Inside these compartments, called lysosomes, eukaryote cells can destroy defective proteins.

All eukaryotes also share a cellular skeleton that they constantly build and tear down to change their shape. Dr. Ettema and his colleagues found many genes in Lokiarchaeum that encode the proteins required to build the skeleton.

The scientists are now trying to grow these cells in the lab to understand more about them, but it’s difficult to replicate the conditions of deep ocean hydrothermal vents. In the meantime they’re looking for more archaea that might be even closer relatives of our eukaryotic ancestors, and in turn telling us more about our own origins.