A new counter theory to the “hard-steps” model of human evolution suggests that intelligent life on Earth and beyond may be more commonplace than previously thought. The theory, published in Science Advances, offers a detailed critique of the hard-steps model and presents an alternative way of understanding why it took billions of years for our species to evolve.
The hard-steps model, proposed by physicist Brandon Carter in 1983, suggests that human-like intelligence emerged on Earth only after a series of extremely unlikely biological events. However, a qualitative review study finds that this idea may be overstated and that each step in the evolutionary process was not as rare as previously thought.
The study’s lead author, Daniel Mills, notes that many evolutionary innovations are repeated throughout history, with examples such as the cellular acquisition of plastids and the evolution of oxygen-producing microorganisms. These findings challenge the assumption that each evolutionary innovation is a singular event.
Furthermore, the likelihood of one evolutionary event is not independent of others, and any particular biological change can alter the environment in ways that prevent similar changes from happening again. This idea is key to the new theory, which suggests that life on Earth has shaped the planet itself.
The study’s authors propose that intelligent life took billions of years to evolve because the windows in which each requisite step was possible were much smaller than previously thought and didn’t arrive until far later in Earth’s history. They also note that the emergence of humans was not a lucky break, but rather a given, spurred by a runaway train of planetary conditions and biological events.
The new theory does not prove the possibility of extraterrestrial existence, but it provides a path forward for future studies. The authors suggest that continued observations of exoplanets, surveying their atmospheres for signs of oxygen, could help clarify what Earth needed to look like for life to first emerge.
Ultimately, the study offers a new way to think about our planet and ourselves, one that challenges the assumption that humans are an evolutionary fluke. If this theory is correct, it would suggest that we are not alone in the universe and that intelligent life may be more common than previously thought.
Source: https://www.popsci.com/science/alien-intelligence-likely