Did life on Earth emerge from two separate biological beginnings?
In short: For decades, we assumed all life descended from a single, free-living cell. However, new research into the deep history of Earth's microbes suggests a more complex story: two independent lineages of life may have emerged from a shared, nonliving ancestor.
A new study published in Science Advances challenges the long-held assumption that all life descended from one single, free-living cell. By tracing the evolutionary history of the two prokaryotic lineages—bacteria and archaea—researchers found evidence that these two groups may have transitioned into independent, free-living existence at two separate times.
The research, led by biologists Natalia Mrnjavac and William Martin from the University of Düsseldorf, focused on the metabolic networks of the Last Universal Common Ancestor, or LUCA. This ancient ancestor likely lived in the early oceans, perhaps near deep-sea hydrothermal vents, where heat and high pressures facilitated spontaneous chemical reactions. The team examined the 420 chemical reactions that constitute the core metabolism used to produce essential building blocks like amino acids, RNA bases, and vitamins.
Crucially, the study found that LUCA was not yet a fully self-sufficient organism. It relied on the environment to perform about half of its core metabolic reactions, using metals from the Earth's crust as catalysts. Over time, as proteins evolved, these environmental metal catalysts were replaced by more efficient enzymes. This transition from geochemical reactions to enzymatic metabolism likely occurred as bacteria and archaea diverged, marking two distinct attempts at life outside the confines of hydrothermal vents.
While the genetic code remains universally conserved, the enzymes driving these metabolic reactions do not show the same level of conservation across the divide between bacteria and archaea. This suggests that while life may share one ancient genetic blueprint, the machinery of life was assembled through two separate evolutionary events.
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Sources
- Summary by Intellect · source: Scientists Find Evidence That Life on Earth Had Two Separate Origins
- Also: A New Study Points to Two Origins of Life on Earth by Tracing Early Chemical Reactions in Single-Celled Organisms
- Also: Scientists find evidence for two origins of life on Earth
- Also: Two origins of life: Free-living cells may have emerged twice as bacteria and archaea diverged
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