YouTube: November 21 (2)

Evolution Tells Us We Might Be the Only Intelligent Life in the Universe Our evolutionary history shows that many key adaptations—not just intelligence, but complex animals, complex cells, photosynthesis, and life itself—were unique, one-off events, and therefore highly improbable. ......... The universe is astonishingly vast. The Milky Way has more than 100 billion stars, and there are over a trillion galaxies in the visible universe, the tiny fraction of the universe we can see. Even if habitable worlds are rare, their sheer number—there are as many planets as stars, maybe more—suggests lots of life is out there. So where is everyone? This is the Fermi paradox. The universe is large, and old, with time and room for intelligence to evolve, but there’s no evidence of it. ............

Remarkably, Australia’s entire evolutionary history, with mammals diversifying after the dinosaur extinction, parallels other continents.

............ Eyes evolved not just in vertebrates, but in arthropods, octopi, worms, and jellyfish. Vertebrates, arthropods, octopi, and worms independently invented jaws. Legs evolved convergently in the arthropods, octopi, and four kinds of fish (tetrapods, frogfish, skates, mudskippers). ........ Complex animals evolved once in life’s history, suggesting they’re improbable. ........ Surprisingly, many critical events in our evolutionary history are unique and, probably, improbable. One is the bony skeleton of vertebrates, which let large animals move onto land. The complex, eukaryotic cells that all animals and plants are built from, containing nuclei and mitochondria, evolved only once. Sex evolved just once. Photosynthesis, which increased the energy available to life and produced oxygen, is a one-off. For that matter, so is human-level intelligence. There are marsupial wolves and moles, but no marsupial humans. .......... All organisms come from a single ancestor; as far as we can tell, life only happened once. ......... Photosynthesis evolved 1.5 billion years after the Earth’s formation, complex cells after 2.7 billion years, complex animals after 4 billion years, and human intelligence 4.5 billion years after the Earth formed. That these innovations are so useful but took so long to evolve implies that they’re exceedingly improbable. ...........

our evolution wasn’t like winning the lottery. It was like winning the lottery again, and again, and again

........ Imagine that intelligence depends on a chain of seven unlikely innovations—the origin of life, photosynthesis, complex cells, sex, complex animals, skeletons, and intelligence itself—each with a 10 percent chance of evolving. The odds of evolving intelligence become one in 10 million. .......... So maybe each of these seven key innovations evolve just 1 percent of the time. If so, intelligence will evolve on just 1 in 100 trillion habitable worlds. If habitable worlds are rare, then we might be the only intelligent life in the galaxy, or even the visible universe.