Right. This has been my preferred solution to the paradox as well, for the last several years. More and more evidence seems to point towards the Drake Equation

Right. This has been my preferred solution to the paradox as well, for the last several years. More and more evidence seems to point towards the Drake Equation simply not sufficiently accounting for uncertainty [1]. There are a few planets and moons in our system that have or had the potential for life, but upon which there's been no evidence for intelligent life, if any life is to be found on them at all: Mars, Europa, Ganymede, among others. While this would seem to increase the probability of life in other solar systems, seeing observable life on only one of the worlds in our system really has a negative impact on the overall odds of life in the universe. Whether a moon is necessary or not for life on Earth [2], it remains that a stable tilt is currently thought to be critical for the development of complex life. We also had the benefit of an asteroid that obliterated the dominant species of the planet and changed the environment sufficiently to allow for new species to take their place. Hundreds of millions of years of flourishing life also provided us with the abundant, cheap energy sources in the forms of coal and oil that we needed to build civilizations. There's also an open question as to whether evolution necessarily leads to intelligent species. Earth had large, complex lifeforms for 165 million years, and none of them appear to have developed civilizations. Human societies have existed for just 50,000 years if you take a very liberal definition of "society". Research has found an evolutionary fluke that fed lots of oxygen-rich blood to hominid brains [3]; other research has suggested that intelligence is not only not an evolutionary advantage, it's a disadvantage, due to the much higher calorie diet required to sustain it. And finally, our universe may not have been hospitable to advanced civilizations until only (geologically) recently. It took a billion years for the universe to form galaxies and stars and planets [4]; it was a more chaotic, hot, radiation-rich universe before our solar system was born. Any civilizations which developed much before our own solar system may have met a premature end by radiation or cosmic debris. Given the empirical lack of observable life in the universe so far, and that continuing research keeps growing rather than reducing the number of special cases that led to human civilization on Earth, it seems likely to me that even if there are other intelligent civilizations in the cosmos, they are approximately as young as we are, too far away and technologically primitive to make contact. [1]: A good paper on this from last year: https://arxiv.org/pdf/1806.02404.pdf https://arxiv.org/pdf/1806.02404.pdf [pdf] [2]: https://www.astrobio.net/news-exclusive/the-odds-for-life-on-a-moonless-earth/ https://www.astrobio.net/news-exclusive/the-odds-for-life-on... [3]: https://theconversation.com/how-our-species-got-smarter-through-a-rush-of-blood-to-the-head-73856 https://theconversation.com/how-our-species-got-smarter-thro... [4]: https://en.wikipedia.org/wiki/Chronology_of_the_universe https://en.wikipedia.org/wiki/Chronology_of_the_universe