Breakthrough Discovery Could Provide Clues to the Age-Old Chicken or Egg Evolution Mystery

For scientists, the question of which came first—the oxygen we breathe or the oxygen produced by plants—has always been puzzling.

Plants and algae create oxygen through photosynthesis. They use sunlight, carbon dioxide, and water to make food, releasing oxygen in the process. In contrast, animals inhale oxygen to turn food into energy through a process known as aerobic metabolism, which simultaneously produces carbon dioxide.

A new study published in the Proceedings of the National Academy of Sciences presents an interesting twist to this age-old debate. Researchers, led by former Harvard fellow Felix Elling, stumbled upon a unique molecule that might help answer this evolutionary riddle.

Elling was investigating different molecules in a nitrogen-utilizing bacterium called Nitrospirota. While looking for specific compounds unrelated to oxygen production, he discovered a molecule that resembled those used in photosynthesis, not the type usually found in bacteria.

This molecule, named methyl-plastoquinone, is a variant of quinones, compounds used in various life forms for metabolic processes. Traditionally, scientists believed there were two main types of quinones: those associated with oxygen and those that aren’t. However, the finding of methyl-plastoquinone suggests a third type, possibly linking photosynthesis and aerobic metabolism.

The research provides insights into the Great Oxidation Event, a time around 2.4 billion years ago when cyanobacteria started producing significant oxygen, enabling aerobic metabolism to develop. This discovery implies that some bacteria might have already been able to use oxygen even before cyanobacteria generated it.

In essence, Elling suggests that both processes might have emerged simultaneously. He explains, “the chicken and the egg were at the same time.”

Professor Ann Pearson, who supervised the research, highlighted the importance of evolving biochemical systems capable of handling oxygen. These systems are vital because oxygen can be harmful to cells without proper safeguards. “The chemical systems we have to manage oxygen are quite sophisticated,” she noted.

This discovery also illuminates how life diversified after oxygen became available. It paved the way for many forms of life that thrive today.

Traces of the evolution of quinone structures exist within us, showing distinct differences between those in plants and those in human mitochondria. Elling believes they have found an ancient version of the molecule that adapted over time for different functions in plants and humans.

Describing the molecule, Elling said, “This molecule is a time capsule—a living fossil that has survived for over 2 billion years.”

For more detailed information, refer to the study by Felix J. Elling et al., which you can find in the Proceedings of the National Academy of Sciences (2025).

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