BREAKING: New research reveals that complex life on Earth began evolving much earlier than previously believed, with origins dating back nearly 2.9 billion years ago. This urgent discovery, published on December 3, 2025 in the journal Nature, challenges long-held assumptions about the timeline of cellular complexity and the role of atmospheric oxygen.
Scientists from the University of Bristol, utilizing an expanded molecular clock method, have unveiled that crucial cellular features emerged in ancient oceans devoid of oxygen, contradicting the traditional view that significant oxygen levels were essential for the rise of complex organisms. This groundbreaking study sheds light on the environmental conditions that fostered early evolution, suggesting a much slower and prolonged development of life’s complexity.
Co-author Anja Spang from the Royal Netherlands Institute for Sea Research stated, “For hundreds of millions of years, prokaryotes were the only living organisms. Complex eukaryotic cells eventually evolved, leading to the emergence of algae, fungi, plants, and animals.”
The research team, including Davide Pisani and Tom Williams, analyzed more than one hundred gene families to better understand the traits distinguishing eukaryotes from prokaryotes. Their findings indicate that the transition toward complexity began significantly earlier than previously estimated, with structures such as the nucleus appearing long before the advent of mitochondria.
“The process of cumulative complexification took place over a much longer time period than previously thought,” said lead author Gergely Szöllösi from the Okinawa Institute of Science and Technology. The results propose a new model for understanding the evolution of complex life, termed ‘CALM’—Complex Archaeon, Late Mitochondrion.
Lead researcher Christopher Kay emphasized the innovative approach used to examine the interactions of gene families and their functions in absolute time. This multi-disciplinary effort combined paleontology, phylogenetics, and molecular biology to illuminate the origins of eukaryotic life.
Notably, the study reveals that mitochondria developed significantly later than previously thought, coinciding with a notable increase in atmospheric oxygen levels. Philip Donoghue remarked, “This insight connects evolutionary biology directly to Earth’s geochemical history,” highlighting the substantial gap between the emergence of complex features and the rise of oxygen in the environment.
These findings not only reshape the narrative of life’s evolution on Earth but also have profound implications for our understanding of biological complexity and its ties to global geochemical changes. As the scientific community processes this urgent update, experts advise closely monitoring further studies that could refine our understanding of life’s origins.
Stay tuned for more updates as this story develops.
