Intelligent Life Could Be More Common Than Previously Believed
A new study from Penn State challenges the long-held belief that intelligent life is rare, suggesting it may be more probable than previously assumed, reports thedebrief.org.
In 1961, Frank Drake introduced the Drake Equation, estimating the likelihood of advanced civilizations in the Milky Way. By 2023, advances in exoplanet science and astrobiology led to refinements, including Sara Seager’s equation focusing on biosignatures.
Previously, physicist Brandon Carter’s 1983 “hard steps” model argued that life is rare due to improbable evolutionary leaps. The Penn State study revisits this model, offering a fresh perspective.
Scientists have long explored planetary habitability using Goldilocks Zones—regions where conditions are “just right” for life. Stephen H. Dole introduced this concept in 1964, examining factors like temperature and liquid water. Seager expanded on this with Hycean worlds, exoplanets with hydrogen-rich atmospheres and oceans that could support life.
The Penn State team, including Daniel B. Mills, Jennifer L. Macalady, Adam Frank, and Jason T. Wright, reassessed the “hard steps” model, focusing on Earth’s evolutionary milestones. The paper was published in Science Advances.
They argue that life evolved “on time” when conditions were suitable, driven by factors like atmospheric oxygen levels. “We’re arguing that intelligent life may not require a series of lucky breaks to exist,” said Mills. “Humans didn’t evolve ‘early’ or ‘late’ in Earth’s history, but ‘on time.’”
The study introduces “windows of habitability”—periods when conditions favored life, controlled by factors like nutrient availability and oxygen levels. Earth only recently stabilized into a state supporting complex life.
“We’re taking the view that rather than base our predictions on the lifespan of the sun, we should use a geological time scale,” said Wright.
Looking ahead, the team plans to study exoplanet atmospheres for biosignatures and examine how environmental factors affect evolution.
“This new perspective suggests that the emergence of intelligent life might not be such a long shot after all,” Wright said.
“Instead of a series of improbable events, evolution may be more of a predictable process, unfolding as global conditions allow. Our framework applies not only to Earth but also other planets, increasing the possibility that life similar to ours could exist elsewhere.”
