Does planetary evolution favor human-like life? Study ups odds we're not alone

Good news! We are not alone! Evolution as a repeatable process of milestones.

"Humanity may not be extraordinary but rather the natural evolutionary outcome for our planet and likely others, according to a new model for how intelligent life developed on Earth. ... 

A team of researchers at Penn State, who led the work, said the new interpretation of humanity's origin increases the probability of intelligent life elsewhere in the universe. ...

In the new study, a team of researchers that included astrophysicists and geobiologists argued that Earth's environment was initially inhospitable to many forms of life, and that key evolutionary steps only became possible when the global environment reached a "permissive" state. ..."

From the abstract:

"According to the “hard-steps” model, the origin of humanity required “successful passage through a number of intermediate steps” (so-called “hard steps”) that were intrinsically improbable in the time available for biological evolution on Earth. This model similarly predicts that technological life analogous to human life on Earth is “exceedingly rare” in the Universe. 

Here, we critically reevaluate core assumptions of the hard-steps model through the lens of historical geobiology. Specifically, we propose an alternative model where there are no hard steps, and evolutionary singularities required for human origins can be explained via mechanisms outside of intrinsic improbability.

Furthermore, if Earth’s surface environment was initially inhospitable not only to human life, but also to certain key intermediate steps required for human existence, then the timing of human origins was controlled by the sequential opening of new global environmental windows of habitability over Earth history."

Does planetary evolution favor human-like life? Study ups odds we're not alone

Does planetary evolution favor human-like life? Study ups odds we’re not alone (original news release) "New theory proposes that humans — and analogous life beyond Earth — may represent the probable outcome of biological and planetary evolution"

A reassessment of the “hard-steps” model for the evolution of intelligent life (open access)

Fig. 1. The temporal distribution of our candidate hard steps.