The Start of It All

Dinosaurs, daisies, starfish and humans are all made up of cells containing tiny biological hitchhikers. In all complex life, each cell has an energy-producing organelles that have their own DNA and look and act suspiciously like bacteria. In animals, there are mitochondria; in plants, there are mitochondria and chloroplasts.

How they got there is an open question and one researchers like Brett Baker, a faculty member in The University of Texas at Austin Department of Marine Science, explore. Baker thinks the answer may go something like this:

• About 2 billion years ago, a microbe called an archaeon gobbled up a free-floating bacterium, and it worked well for both parties. The bacterium provided new energy sources to the archaeon, which in turn provided safety and nutrients.

Early Archaeon

Bacterium

Archaeon gobbling up bacteria

• Over time the two previously free-living microbes spawned a single, hybrid offspring — the first eukaryote.

• All complex, multicellular life on the planet evolved from this new lifeform.

Eukaryote with mitochondria

Baker and his colleagues have uncovered evidence that a recently discovered group of microbes, called the Asgard archaea, were the original hosts to give rise to all eukaryotes, including us humans. With support from the Moore-Simons Project, the scientists are now investigating which Asgards are most closely related to eukaryotes and further exploring their physiological interactions and cellular structure.

Image Sequence Attribution: “Kelvinsong”/Wikimedia Commons (CC BY-SA 3.0)