For the first time in one billion years, two lifeforms truly merged into one organism

https://www.popsci.com/science/two-lifeforms-merged-into-one/

“… a team of scientists have detected a sign of a major life event that has likely not occurred for at least one billion years. They’ve observed primary endosymbiosis–two lifeforms merging into one organism. This incredibly rare event occurred between a type of abundant marine algae and a bacterium was observed in a lab setting. For perspective, plants first began to dot our planet the last time this happened. The results are described in two papers recently published in the journals Cell and Science.

Primary endosymbiosis happens when one microbial organism engulfs another. It then begins to use the swallowed organisms as an internal organ. The host provides the organism–now called an endosymbiont–several benefits including nutrients, energy, and protection. When it can no longer survive on its own, the engulfed endosymbiont becomes an organ for the host called an organelle.

“It’s very rare that organelles arise from these types of things,” Tyler Coale, a co-author of the Cell study and a postdoctoral scholar at the University of California, Santa Cruz said in a statement. “The first time we think it happened, it gave rise to all complex life.”

Endosymbiosis where the host life form becomes fundamental to another organism’s function has only happened three known times. All of these instances were a major breakthroughs for evolution, since merging with their hosts became fundamental for the endosymbionts very existence.

The referenced article notes these earlier instances include when the single celled archaea engulfed a bacterium that eventually resulted in formation of mitochondria, about 2.2 billion years ago; and when more advanced organisms incorporated Cyanobacteria that resulted in formation of chloroplasts.

The lab-observed event could give rise to organisms capable of nitrogen fixation.