New research suggests that humans may not be extraordinary existences but the result of the natural evolution of the Earth (and possibly other planets). This study attempts to overturn the decades-old “Hard-Steps theory” that believes the emergence of intelligent life is an extremely low-probability event. The new explanation of the study raises the possibility of other intelligent life in the universe.

The Hard-Steps theory, proposed by theoretical physicists in 1983, believes that human evolution takes too long compared to the sun’s lifespan, showing that the probability of intelligent life is extremely low. If some key steps in biological evolution steps take too long (the so-called Hard Step), the probability of smart life appearing is extremely low. Based on this, the Hard-Step theory predicts that there is almost no intelligent civilization in the universe.

Recent research challenges the evolutionary singularity and low probability hypothesis of the Hard-Steps theory. Traditionally, the origin of life, oxygenation photosynthesis, eukaryotic cells, multicellularity, and the emergence of Homo sapiens are all “evolutionary singularities,” that is, they only appeared once in the history of the earth, so they are regarded as low-probability events. However, the study explores in-depth the singularity that may be due to the loss of messages or the evolutionary competitive advantage of geological time. For example, if other independently evolved life forms became extinct in early Earth environments, the only remaining branches of modern biodiversity would give the illusion of singularity. In addition, the first-time species may have an advantage in the ecological niche, inhibiting the chance of subsequent recurrence. This “evolutionary advantage” makes the singularity appear extremely low.

The paper describes the changes in the Earth’s environment in detail and emphasizes that the rise in oxygen concentration is crucial to the evolution of complex life. In particular, the Great Oxidation Event and the Paleozoic Oxygenation Event have increased the atmospheric oxygen content, providing the necessary conditions for eukaryotic cells, animal multicellularity, and the ultimate evolution of intelligent life. These environmental changes are called the opening of the “living window,” that is, the Earth’s surface environment reaches a state suitable for the evolution of complex life.

The paper points out that the opening of the living window is not accidental, but is driven by the interaction between the Earth’s environment and life, such as the increase in the sun’s luminosity, the formation and division of supercontinents, climate change, and the evolution of the biosphere. The first author explained: “We believe that the emergence of intelligent life may not require a series of lucky events. Human beings do not appear ‘too early’ or ‘too late’ in the history of the Earth, but rather appear ‘on-time’ when the environmental conditions are appropriate.” If intelligent life evolution is mainly controlled by the habitable window, and the probability that the universe has similar intelligent life may be much higher than traditional models predict. This view changes our view on the origin of life and the rarity of intelligent life, and also finds a new direction for the search for extraterrestrial intelligent life.

The paper was completed by cross-domain collaboration between astronomers, physicists, and geobiologists to reexamine the process of life’s evolution on planets. The new model provides a more predictive and testable framework that believes that the evolution of intelligent life is a natural result of planetary environment changes rather than a coincidence of a series of low-probability events.

This research has significant implications for the search for extraterrestrial life. If the conditions for the emergence of intelligent life are more common than previously thought, it increases the likelihood of finding life beyond Earth. For instance, missions like NASA’s Mars 2020 Perseverance rover, which is currently exploring Mars for signs of ancient life, could benefit from this new perspective. The rover is equipped with advanced instruments to search for biosignatures and understand the planet’s habitability.

However, some scientists argue that the Hard-Steps theory still holds weight. They point out that while the new research provides compelling evidence, it does not account for all the variables that could influence the emergence of intelligent life. For example, the presence of a large moon stabilizing Earth’s axial tilt, which is crucial for climate stability, is a unique feature of our planet that may not be replicated elsewhere. Additionally, the role of plate tectonics in recycling nutrients and regulating climate is another factor that could be essential for the evolution of complex life.

Despite these counterarguments, the new research offers a fresh perspective on the likelihood of intelligent life in the universe. It encourages further investigation into the conditions that favor the emergence of complex life and the potential for life beyond Earth. As we continue to explore the cosmos, this research provides a valuable framework for understanding the natural processes that could lead to the evolution of intelligent life.