The evolution of humans on Earth may not be entirely exceptional. That is because intelligent life is likely to form if certain planetary conditions are met, a new study suggests. This idea displaces the previously-held belief that humanity's appearance occurred thanks to a highly improbable series of events.
Evolutionary ends
For a long time, scientists believed that human life on Earth only came about by chance, and therefore the formation of intelligent life in other places would be equally far-fetched. However, a new paper published in the journal Science Advances found that there were no "hard steps" required for humans to evolve and that life is likely to have formed elsewhere in the universe as well. "Homo sapiens and analogous extraterrestrial life forms may be the probable end result of biological and planetary evolution when a planet has a certain set of attributes that make it habitable, rather than requiring countless lucky breaks," said Reuters.
The theory that intelligent life forming on Earth was an incredible occurrence first originated in a 1983 paper by Australian physicist Brandon Carter, which said that the "evolutionary chain included at least one but probably not more than two links that were highly improbable (a priori) in the available time interval." Carter posited that because it took so long for human life to form on Earth, it must be difficult, making the existence of humans entirely a fluke. But this new study identified a fallacy in Carter's reasoning.
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Carter "specifically assumed that the age of the sun, and therefore the Earth, should have no bearing on how quickly complex life evolved," said Space.com. Researchers now say that is not true. "Life might have originated very quickly once temperatures were appropriate for the stability of biomolecules and liquid water," said Jennifer Macalady, a study co-author and microbiology professor at Pennsylvania State University, to Reuters. "The Earth has only been habitable for humans since the second rise of oxygen in the atmosphere approximately 0.5 billion years ago, meaning that humans could not have evolved on Earth prior to that relatively recent moment." Essentially, life on Earth evolved exactly when it was supposed to.
Alien applications
While this is not direct proof of the existence of aliens, it does mean "our existence is probably not an evolutionary fluke," Macalady said to Popular Science. "We're an expected or predictable outcome of our planet's evolution, just as any other intelligent life out there will be." In turn, "maybe other planets are able to achieve these conditions more rapidly than Earth did, while other planets might take even longer," said a release on the paper. There are still unanswered questions. For example, scientists do not know the origin of life on Earth. "This moment of genesis is currently lost in the mists of time, and we cannot yet say whether it was a fluke one-off event or whether it was an easy step," said Space.com.
While the new paper is not proof that intelligent life was intended to happen, it does offer a different perspective on evolution. The theory also opens the door to the consideration of intelligent life after humans on Earth. "If we were to go extinct, some other form of intelligent life could readily emerge in our stead," said Popular Science. "And humanity is less likely to be alone in the universe than we thought."
