For years, the prevailing scientific view has been that intelligent life is a cosmic rarity — a fluke requiring multiple improbable evolutionary breakthroughs, as proposed by the “hard steps” theory. However, a recent study led by Dr. Daniel Mills, a geobiologist and postdoctoral scholar at the University of Munich, upends this assumption, potentially reshaping our entire approach to the hunt for intelligent alien civilizations.

In a recent episode of SETI Live, Dr. Franck Marchis, a senior planetary astronomer, and Dr. Mills explored the idea that intelligent life could be an inevitable result of planetary evolution. Many important topics were raised in this discussion:

New research challenges the “hard steps” theory, which claims intelligent life is rare due to improbable evolutionary leaps, suggesting instead that it may be a predictable outcome of planetary evolution.  Dr. Daniel Mills proposes “windows of habitability”— periods in a planet’s history where environmental conditions naturally allow complex life to emerge, rather than requiring unlikely chance events. Earth’s history supports this idea, with major evolutionary milestones (like oxygen-dependent life) aligning with environmental shifts in oxygen levels, temperature, tectonics and nutrient availability: the Great Oxidation Event (2.3 billion years ago) was a key turning point, gradually transforming Earth’s atmosphere and enabling more complex life forms to evolve.

Multiple factors influence habitability, including ocean chemistry, photosynthetic productivity, and plate tectonics—all of which create temporary “windows” for life to thrive. Earth still has 1–1.5 billion years of habitability left, meaning another intelligent species could evolve even if humanity goes extinct.

Interdisciplinary collaboration is crucial — Mills works with astronomers, biologists and geologists to understand how planetary conditions shape the rise of intelligence.

All this boosts optimism for SETI, as intelligent life may be far more common if it emerges predictably under the right planetary conditions.

For more detailed information and link to the SETI Live episode, read the article by SETI Institute.