An amazing event, the third of its kind in human history the merging of two organisms into one living body

An international team of scientists has observed the merging of two life forms into one organism, for the first time in at least a billion years.  

This process, called primary endosymbiosis, has only occurred twice in Earth's history. The first time led to the emergence of all complex life as we know it through mitochondria (responsible for producing energy in the body's cells) ,  and the second time saw the emergence of plants.

Now, scientists from the United States and Japan have discovered this evolutionary event between species of algae, commonly found in the ocean, and bacteria.

"The first time, the event gave rise to all complex life," said Tyler Cole, a postdoctoral researcher at the University of California, Santa Cruz. "And a billion years ago or so, it happened again with chloroplasts, which gave us plants."

The process involves the algae ingesting the bacteria and providing them with nutrients, energy and protection in exchange for functions they were not previously able to perform. In this case, the ability to "fix" nitrogen from the air.

Next, the algae integrates the bacteria into an internal organ called an organelle.

"This system is a new perspective on nitrogen fixation, and may provide clues about how to engineer such an organelle into crop plants," Cole said.

Scientists explained that this discovery will provide new insights into the evolutionary process, while also holding the potential to radically change agriculture.

Papers detailing the research have been published in Science and Cell.